Patent Publication Number: US-10316196-B2

Title: Mixed cation perovskite material devices

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/866,150 filed Sep. 25, 2015 and entitled “Bi- and Tri- Layer Interfacial Layers in Perovskite Material Device,” which is a continuation of U.S. application Ser. No. 14/711,391 filed May 13, 2015 and entitled “Bi- and Tri- Layer Interfacial Layers in Perovskite Material Device”which is based upon and claims priority to (1) U.S. Provisional Patent Application Ser. No. 62/083,063, entitled “Bi- and Tri- Layer Interfacial Layers in Perovskite Material Devices,” filed 21 Nov. 2014; and (2) U.S. Provisional Patent Application Ser. No. 62/032,137, entitled “Method of Formulating Perovskite Solar Cell Materials,” filed 1 Aug. 2014; and which is a continuation-in-part of application Ser. No. 14/448,053, entitled “Perovskite Solar Cell Materials,”filed 31 Jul. 2014, which, in turn, claims priority to (1) U.S. Provisional Patent Application Ser. No. 61/909,168, entitled “Solar Cell Materials,” filed 26 Nov. 2013; and (2) U.S. Provisional Patent Application Ser. No. 61/913,665, entitled “Perovskite Solar Cell Materials,” filed 9 Dec. 2013. 
    
    
     BACKGROUND 
     Use of photovoltaics (PVs) to generate electrical power from solar energy or radiation may provide many benefits, including, for example, a power source, low or zero emissions, power production independent of the power grid, durable physical structures (no moving parts), stable and reliable systems, modular construction, relatively quick installation, safe manufacture and use, and good public opinion and acceptance of use. 
     The features and advantages of the present disclosure will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of DSSC design depicting various layers of the DSSC according to some embodiments of the present disclosure. 
         FIG. 2  is another illustration of DSSC design depicting various layers of the DSSC according to some embodiments of the present disclosure. 
         FIG. 3  is an example illustration of BHJ device design according to some embodiments of the present disclosure. 
         FIG. 4  is a schematic view of a typical photovoltaic cell including an active layer according to some embodiments of the present disclosure. 
         FIG. 5  is a schematic of a typical solid state DSSC device according to some embodiments of the present disclosure. 
         FIG. 6  is a stylized diagram illustrating components of an example PV device according to some embodiments of the present disclosure. 
         FIG. 7  is a stylized diagram showing components of an example PV device according to some embodiments of the present disclosure. 
         FIG. 8  is a stylized diagram showing components of an example PV device according to some embodiments of the present disclosure. 
         FIG. 9  is a stylized diagram showing components of an example PV device according to some embodiments of the present disclosure. 
         FIG. 10  is a stylized diagram of a perovskite material device according to some embodiments. 
         FIG. 11  is a stylized diagram of a perovskite material device according to some embodiments. 
         FIG. 12  shows images from a cross-sectional scanning electron microscope comparing a perovskite PV fabricated with water (top) and without water (bottom). 
         FIGS. 13-20  are stylized diagrams of perovskite material devices according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Improvements in various aspects of PV technologies compatible with organic, non-organic, and/or hybrid PVs promise to further lower the cost of both organic PVs and other PVs. For example, some solar cells, such as solid-state dye-sensitized solar cells, may take advantage of novel cost-effective and high-stability alternative components, such as solid-state charge transport materials (or, colloquially, “solid state electrolytes”). In addition, various kinds of solar cells may advantageously include interfacial and other materials that may, among other advantages, be more cost-effective and durable than conventional options currently in existence. 
     The present disclosure relates generally to compositions of matter, apparatus and methods of use of materials in photovoltaic cells in creating electrical energy from solar radiation. More specifically, this disclosure relates to photoactive and other compositions of matter, as well as apparatus, methods of use, and formation of such compositions of matter. 
     Examples of these compositions of matter may include, for example, hole-transport materials, and/or materials that may be suitable for use as, e.g., interfacial layers (IFLs), dyes, and/or other elements of PV devices. Such compounds may be deployed in a variety of PV devices, such as heterojunction cells (e.g., bilayer and bulk), hybrid cells (e.g., organics with CH 3 NH 3 PbI 3 , ZnO nanorods or PbS quantum dots), and DSSCs (dye-sensitized solar cells). The latter, DSSCs, exist in three forms: solvent-based electrolytes, ionic liquid electrolytes, and solid-state hole transporters (or solid-state DSSCs, i.e., SS-DSSCs). SS-DSSC structures according to some embodiments may be substantially free of electrolyte, containing rather hole-transport materials such as spiro-OMeTAD, CsSnI 3 , and other active materials. 
     Some or all of materials in accordance with some embodiments of the present disclosure may also advantageously be used in any organic or other electronic device, with some examples including, but not limited to: batteries, field-effect transistors (FETs), light-emitting diodes (LEDs), non-linear optical devices, memristors, capacitors, rectifiers, and/or rectifying antennas. 
     In some embodiments, the present disclosure may provide PV and other similar devices (e.g., batteries, hybrid PV batteries, multi junction PVs, FETs, LEDs etc.). Such devices may in some embodiments include improved active material, interfacial layers, and/or one or more perovskite materials. A perovskite material may be incorporated into various of one or more aspects of a PV or other device. A perovskite material according to some embodiments may be of the general formula CMX 3 , where: C comprises one or more cations (e.g., an amine, ammonium, a Group 1 metal, a Group 2 metal, and/or other cations or cation-like compounds); M comprises one or more metals (examples including Fe, Co, Ni, Cu, Sn, Pb, Bi, Ge, Ti, and Zr); and X comprises one or more anions. Perovskite materials according to various embodiments are discussed in greater detail below. 
     Photovoltaic Cells and Other Electronic Devices 
     Some PV embodiments may be described by reference to various illustrative depictions of solar cells as shown in  FIGS. 1, 3, 4, and 5 . For example, an example PV architecture according to some embodiments may be substantially of the form substrate-anode-IFL-active layer-IFL-cathode. The active layer of some embodiments may be photoactive, and/or it may include photoactive material. Other layers and materials may be utilized in the cell as is known in the art. Furthermore, it should be noted that the use of the term “active layer” is in no way meant to restrict or otherwise define, explicitly or implicitly, the properties of any other layer—for instance, in some embodiments, either or both IFLs may also be active insofar as they may be semiconducting. In particular, referring to  FIG. 4 , a stylized generic PV cell  2610  is depicted, illustrating the highly interfacial nature of some layers within the PV. The PV  2610  represents a generic architecture applicable to several PV devices, such as perovskite material PV embodiments. The PV cell  2610  includes a transparent layer  2612  of glass (or material similarly transparent to solar radiation) which allows solar radiation  2614  to transmit through the layer. The transparent layer of some embodiments may also be referred to as a substrate (e.g., as with substrate layer  1507  of  FIG. 1 ), and it may comprise any one or more of a variety of rigid or flexible materials such as: glass, polyethylene, PET, Kapton, quartz, aluminum foil, gold foil, or steel. The photoactive layer  2616  is composed of electron donor or p-type material  2618 , and/or an electron acceptor or n-type material  2620 , and/or an ambipolar semiconductor, which exhibits both p- and n-type material characteristics. The active layer or, as depicted in  FIG. 4 , the photo-active layer  2616 , is sandwiched between two electrically conductive electrode layers  2622  and  2624 . In  FIG. 4 , the electrode layer  2622  is a tin-doped indium oxide (ITO material). As previously noted, an active layer of some embodiments need not necessarily be photoactive, although in the device shown in  FIG. 4 , it is. The electrode layer  2624  is an aluminum material. Other materials may be used as is known in the art. The cell  2610  also includes an interfacial layer (IFL)  2626 , shown in the example of  FIG. 4  as a ZnO material. The IFL may assist in charge separation. In some embodiments, the IFL  2626  may comprise an organic compound according to the present disclosure as a self-assembled monolayer (SAM) or as a thin film. In other embodiments, the IFL  2626  may comprise a multi-layer IFL, which is discussed in greater detail below. There also may be an IFL  2627  adjacent to electrode  2624 . In some embodiments, the IFL  2627  adjacent to electrode  2624  may also or instead comprise an organic compound according to the present disclosure as a self-assembled monolayer (SAM) or as a thin film. In other embodiments, the IFL  2627  adjacent to electrode  2624  may also or instead comprise a multi-layer IFL (again, discussed in greater detail below). An IFL according to some embodiments may be semiconducting in character and may be either p-type or n-type, or it may be dielectric in character. In some embodiments, the IFL on the cathode side of the device (e.g., IFL  2627  as shown in  FIG. 4 ) may be p-type, and the IFL on the anode side of the device (e.g., IFL  2626  as shown in  FIG. 4 ) may be n-type. In other embodiments, however, the cathode-side IFL may be n-type and the anode-side IFL may be p-type. The cell  2610  is attached to leads  2630  and a discharge unit  2632 , such as a battery. 
     Yet further embodiments may be described by reference to  FIG. 3 , which depicts a stylized BHJ device design, and includes: glass substrate  2401 ; ITO (tin-doped indium oxide) electrode  2402 ; interfacial layer (IFL)  2403 ; photoactive layer  2404 ; and LiF/Al cathodes  2405 . The materials of BHJ construction referred to are mere examples; any other BHJ construction known in the art may be used consistent with the present disclosure. In some embodiments, the photoactive layer  2404  may comprise any one or more materials that the active or photoactive layer  2616  of the device of  FIG. 4  may comprise. 
       FIG. 1  is a simplified illustration of DSSC PVs according to some embodiments, referred to here for purposes of illustrating assembly of such example PVs. An example DSSC as shown in  FIG. 1  may be constructed according to the following: electrode layer  1506  (shown as fluorine-doped tin oxide, FTO) is deposited on a substrate layer  1507  (shown as glass). Mesoporous layer ML  1505  (which may in some embodiments be TiO 2 ) is deposited onto the electrode layer  1506 , then the photoelectrode (so far comprising substrate layer  1507 , electrode layer  1506 , and mesoporous layer  1505 ) is soaked in a solvent (not shown) and dye  1504 . This leaves the dye  1504  bound to the surface of the ML. A separate counter-electrode is made comprising substrate layer  1501  (also shown as glass) and electrode layer  1502  (shown as Pt/FTO). The photoelectrode and counter-electrode are combined, sandwiching the various layers  1502 - 1506  between the two substrate layers  1501  and  1507  as shown in  FIG. 1 , and allowing electrode layers  1502  and  1506  to be utilized as a cathode and anode, respectively. A layer of electrolyte  1503  is deposited either directly onto the completed photoelectrode after dye layer  1504  or through an opening in the device, typically a hole pre-drilled by sand-blasting in the counter-electrode substrate  1501 . The cell may also be attached to leads and a discharge unit, such as a battery (not shown). Substrate layer  1507  and electrode layer  1506 , and/or substrate layer  1501  and electrode layer  1502  should be of sufficient transparency to permit solar radiation to pass through to the photoactive dye  1504 . In some embodiments, the counter-electrode and/or photoelectrode may be rigid, while in others either or both may be flexible. The substrate layers of various embodiments may comprise any one or more of: glass, polyethylene, PET, Kapton, quartz, aluminum foil, gold foil, and steel. In certain embodiments, a DSSC may further include a light harvesting layer  1601 , as shown in  FIG. 2 , to scatter incident light in order to increase the light&#39;s path length through the photoactive layer of the device (thereby increasing the likelihood the light is absorbed in the photoactive layer). 
     In other embodiments, the present disclosure provides solid state DSSCs. Solid-state DSSCs according to some embodiments may provide advantages such as lack of leakage and/or corrosion issues that may affect DSSCs comprising liquid electrolytes. Furthermore, a solid-state charge carrier may provide faster device physics (e.g., faster charge transport). Additionally, solid-state electrolytes may, in some embodiments, be photoactive and therefore contribute to power derived from a solid-state DSSC device. 
     Some examples of solid state DSSCs may be described by reference to  FIG. 5 , which is a stylized schematic of a typical solid state DSSC. As with the example solar cell depicted in, e.g.,  FIG. 4 , an active layer comprised of first and second active (e.g., conducting and/or semi-conducting) material ( 2810  and  2815 , respectively) is sandwiched between electrodes  2805  and  2820  (shown in  FIG. 5  as Pt/FTO and FTO, respectively). In the embodiment shown in  FIG. 5 , the first active material  2810  is p-type active material, and comprises a solid-state electrolyte. In certain embodiments, the first active material  2810  may comprise an organic material such as spiro-OMeTAD and/or poly(3-hexylthiophene), an inorganic binary, ternary, quaternary, or greater complex, any solid semiconducting material, or any combination thereof. In some embodiments, the first active material may additionally or instead comprise an oxide and/or a sulfide, and/or a selenide, and/or an iodide (e.g., CsSnI 3 ). Thus, for example, the first active material of some embodiments may comprise solid-state p-type material, which may comprise copper indium sulfide, and in some embodiments, it may comprise copper indium gallium selenide. The second active material  2815  shown in  FIG. 5  is n-type active material and comprises TiO 2  coated with a dye. In some embodiments, the second active material may likewise comprise an organic material such as spiro-OMeTAD, an inorganic binary, ternary, quaternary, or greater complex, or any combination thereof. In some embodiments, the second active material may comprise an oxide such as alumina, and/or it may comprise a sulfide, and/or it may comprise a selenide. Thus, in some embodiments, the second active material may comprise copper indium sulfide, and in some embodiments, it may comprise copper indium gallium selenide metal. The second active material  2815  of some embodiments may constitute a mesoporous layer. Furthermore, in addition to being active, either or both of the first and second active materials  2810  and  2815  may be photoactive. In other embodiments (not shown in  FIG. 5 ), the second active material may comprise a solid electrolyte. In addition, in embodiments where either of the first and second active material  2810  and  2815  comprise a solid electrolyte, the PV device may lack an effective amount of liquid electrolyte. Although shown and referred to in  FIG. 5  as being p-type, a solid state layer (e.g., first active material comprising solid electrolyte) may in some embodiments instead be n-type semiconducting. In such embodiments, then, the second active material (e.g., TiO 2  (or other mesoporous material) as shown in  FIG. 5 ) coated with a dye may be p-type semiconducting (as opposed to the n-type semiconducting shown in, and discussed with respect to,  FIG. 5 ). 
     Substrate layers  2801  and  2825  (both shown in  FIG. 5  as glass) form the respective external top and bottom layers of the example cell of  FIG. 5 . These layers may comprise any material of sufficient transparency to permit solar radiation to pass through to the active/photoactive layer comprising dye, first and second active and/or photoactive material  2810  and  2815 , such as glass, polyethylene, PET, Kapton, quartz, aluminum foil, gold foil, and/or steel. Furthermore, in the embodiment shown in  FIG. 5 , electrode  2805  (shown as Pt/FTO) is the cathode, and electrode  2820  is the anode. As with the example solar cell depicted in  FIG. 4 , solar radiation passes through substrate layer  2825  and electrode  2820  into the active layer, whereupon at least a portion of the solar radiation is absorbed so as to produce one or more excitons to enable electrical generation. 
     A solid state DSSC according to some embodiments may be constructed in a substantially similar manner to that described above with respect to the DSSC depicted as stylized in  FIG. 1 . In the embodiment shown in  FIG. 5 , p-type active material  2810  corresponds to electrolyte  1503  of  FIG. 1 ; n-type active material  2815  corresponds to both dye  1504  and ML  1505  of  FIG. 1 ; electrodes  2805  and  2820  respectively correspond to electrode layers  1502  and  1506  of  FIG. 1 ; and substrate layers  2801  and  2825  respectively correspond to substrate layers  1501  and  1507 . 
     Various embodiments of the present disclosure provide improved materials and/or designs in various aspects of solar cell and other devices, including among other things, active materials (including hole-transport and/or electron-transport layers), interfacial layers, and overall device design. 
     Interfacial Layers 
     The present disclosure, in some embodiments, provides advantageous materials and designs of one or more interfacial layers within a PV, including thin-coat IFLs. Thin-coat IFLs may be employed in one or more IFLs of a PV according to various embodiments discussed herein. 
     According to various embodiments, devices may optionally include an interfacial layer between any two other layers and/or materials, although devices need not contain any interfacial layers. For example, a perovskite material device may contain zero, one, two, three, four, five, or more interfacial layers (such as the example device of  FIG. 7 , which contains five interfacial layers  3903 ,  3905 ,  3907 ,  3909 , and  3911 ). An interfacial layer may include any suitable material for enhancing charge transport and/or collection between two layers or materials; it may also help prevent or reduce the likelihood of charge recombination once a charge has been transported away from one of the materials adjacent to the interfacial layer. An interfacial layer may additionally physically and electrically homogenize its substrates to create variations in substrate roughness, dielectric constant, adhesion, creation or quenching of defects (e.g., charge traps, surface states). Suitable interfacial materials may include any one or more of: Al; Bi; Co; Cu; Fe; In; Mn; Mo; Ni; platinum (Pt); Si; Sn; Ta; Ti; V; W; Nb; Zn; Zr; oxides of any of the foregoing metals (e.g., alumina, silica, titania); a sulfide of any of the foregoing metals; a nitride of any of the foregoing metals; functionalized or non-functionalized alkyl silyl groups; graphite; graphene; fullerenes; carbon nanotubes; any mesoporous material and/or interfacial material discussed elsewhere herein; and combinations thereof (including, in some embodiments, bilayers of combined materials). In some embodiments, an interfacial layer may include perovskite material. Further, interfacial layers may comprise doped embodiments of any interfacial material mentioned herein (e.g., Y-doped ZnO, N-doped single-wall carbon nanotubes). 
     First, as previously noted, one or more IFLs (e.g., either or both IFLs  2626  and  2627  as shown in  FIG. 4 ) may comprise a photoactive organic compound of the present disclosure as a self-assembled monolayer (SAM) or as a thin film. When a photoactive organic compound of the present disclosure is applied as a SAM, it may comprise a binding group through which it may be covalently or otherwise bound to the surface of either or both of the anode and cathode. The binding group of some embodiments may comprise any one or more of COOH, SiX 3  (where X may be any moiety suitable for forming a ternary silicon compound, such as Si(OR) 3  and SiCl 3 ), SO 3 , PO 4 OH, OH, CH 2 X (where X may comprise a Group 17 halide), and O. The binding group may be covalently or otherwise bound to an electron-withdrawing moiety, an electron donor moiety, and/or a core moiety. The binding group may attach to the electrode surface in a manner so as to form a directional, organized layer of a single molecule (or, in some embodiments, multiple molecules) in thickness (e.g., where multiple photoactive organic compounds are bound to the anode and/or cathode). As noted, the SAM may attach via covalent interactions, but in some embodiments it may attach via ionic, hydrogen-bonding, and/or dispersion force (i,e., Van Der Waals) interactions. Furthermore, in certain embodiments, upon light exposure, the SAM may enter into a zwitterionic excited state, thereby creating a highly-polarized IFL, which may direct charge carriers from an active layer into an electrode (e.g., either the anode or cathode). This enhanced charge-carrier injection may, in some embodiments, be accomplished by electronically poling the cross-section of the active layer and therefore increasing charge-carrier drift velocities towards their respective electrode (e.g., hole to anode; electrons to cathode). Molecules for anode applications of some embodiments may comprise tunable compounds that include a primary electron donor moiety bound to a core moiety, which in turn is bound to an electron-withdrawing moiety, which in turn is bound to a binding group. In cathode applications according to some embodiments, IFL molecules may comprise a tunable compound comprising an electron poor moiety bound to a core moiety, which in turn is bound to an electron donor moiety, which in turn is bound to a binding group. When a photoactive organic compound is employed as an IFL according to such embodiments, it may retain photoactive character, although in some embodiments it need not be photoactive. 
     In addition or instead of a photoactive organic compound SAM IFL, a PV according to some embodiments may include a thin interfacial layer (a “thin-coat interfacial layer” or “thin-coat IFL”) coated onto at least a portion of either the first or the second active material of such embodiments (e.g., first or second active material  2810  or  2815  as shown in  FIG. 5 ). And, in turn, at least a portion of the thin-coat IFL may be coated with a dye. The thin-coat IFL may be either n- or p-type; in some embodiments, it may be of the same type as the underlying material (e.g., TiO 2  or other mesoporous material, such as TiO 2  of second active material  2815 ). The second active material may comprise TiO 2  coated with a thin-coat IFL comprising alumina (e.g., Al 2 O 3 ) (not shown in  FIG. 5 ), which in turn is coated with a dye. References herein to TiO 2  and/or titania are not intended to limit the ratios of tin and oxide in such tin-oxide compounds described herein. That is, a titania compound may comprise titanium in any one or more of its various oxidation states (e.g., titanium I, titanium II, titanium III, titanium IV), and thus various embodiments may include stoichiometric and/or non-stoichiometric amounts of titanium and oxide. Thus, various embodiments may include (instead or in addition to TiO 2 ) Ti x O y , where x may be any value, integer or non-integer, between 1 and 100. In some embodiments, x may be between approximately 0.5 and 3. Likewise, y may be between approximately 1.5 and 4 (and, again, need not be an integer). Thus, some embodiments may include, e.g., TiO 2  and/or Ti 2 O 3 . In addition, titania in whatever ratios or combination of ratios between titanium and oxide may be of any one or more crystal structures in some embodiments, including any one or more of anatase, rutile, and amorphous. 
     Other example metal oxides for use in the thin-coat IFL of some embodiments may include semiconducting metal oxides, such as NiO, WO 3 , V 2 O 5 , or MoO 3 . The embodiment wherein the second (e.g., n-type) active material comprises TiO 2  coated with a thin-coat IFL comprising Al 2 O 3  could be famed, for example, with a precursor material such as Al(NO 3 ) 3 .xH 2 O, or any other material suitable for depositing Al 2 O 3  onto the TiO 2 , followed by thermal annealing and dye coating. In example embodiments wherein a MoO 3  coating is instead used, the coating may be formed with a precursor material such as Na 2 Mo 4 .2H 2 O; whereas a V 2 O 5  coating according to some embodiments may be formed with a precursor material such as NaVO 3 ; and a WO 3  coating according to some embodiments may be formed with a precursor material such as NaWO 4 .H 2 O. The concentration of precursor material (e.g., Al(NO 3 ) 3 .xH 2 O) may affect the final film thickness (here, of Al 2 O 3 ) deposited on the TiO 2  or other active material. Thus, modifying the concentration of precursor material may be a method by which the final film thickness may be controlled. For example, greater film thickness may result from greater precursor material concentration. Greater film thickness may not necessarily result in greater PCE in a PV device comprising a metal oxide coating. Thus, a method of some embodiments may include coating a TiO 2  (or other mesoporous) layer using a precursor material having a concentration in the range of approximately 0.5 to 10.0 mM; other embodiments may include coating the layer with a precursor material having a concentration in the range of approximately 2.0 to 6.0 mM; or, in other embodiments, approximately 2.5 to 5.5 mM. 
     Furtheinfore, although referred to herein as Al 2 O 3  and/or alumina, it should be noted that various ratios of aluminum and oxygen may be used in forming alumina. Thus, although some embodiments discussed herein are described with reference to Al 2 O 3 , such description is not intended to define a required ratio of aluminum in oxygen. Rather, embodiments may include any one or more aluminum-oxide compounds, each having an aluminum oxide ratio according to Al x O y , where x may be any value, integer or non-integer, between approximately 1 and 100. In some embodiments, x may be between approximately 1 and 3 (and, again, need not be an integer). Likewise, y may be any value, integer or non-integer, between 0.1 and 100. In some embodiments, y may be between 2 and 4 (and, again, need not be an integer). In addition, various crystalline forms of Al x O y  may be present in various embodiments, such as alpha, gamma, and/or amorphous forms of alumina. 
     Likewise, although referred to herein as MoO 3 , WO 3 , and V 2 O 5 , such compounds may instead or in addition be represented as Mo x O y , W x O y , and V x O y , respectively. Regarding each of Mo x O y  and W x O y , x may be any value, integer or non-integer, between approximately 0.5 and 100; in some embodiments, it may be between approximately 0.5 and 1.5. Likewise, y may be any value, integer or non-integer, between approximately 1 and 100. In some embodiments, y may be any value between approximately 1 and 4. Regarding V x O y , x may be any value, integer or non-integer, between approximately 0.5 and 100; in some embodiments, it may be between approximately 0.5 and 1.5. Likewise, y may be any value, integer or non-integer, between approximately 1 and 100; in certain embodiments, it may be an integer or non-integer value between approximately 1 and 10. 
     Similarly, references in some illustrative embodiments herein to CsSnI 3  are not intended to limit the ratios of component elements in the cesium-tin-iodine compounds according to various embodiments. Some embodiments may include stoichiometric and/or non-stoichiometric amounts of tin and iodide, and thus such embodiments may instead or in addition include various ratios of cesium, tin, and iodine, such as any one or more cesium-tin-iodine compounds, each having a ratio of Cs x Sn y I z . In such embodiments, x may be any value, integer or non-integer, between 0.1 and 100. In some embodiments, x may be between approximately 0.5 and 1.5 (and, again, need not be an integer). Likewise, y may be any value, integer or non-integer, between 0.1 and 100. In some embodiments, y may be between approximately 0.5 and 1.5 (and, again, need not be an integer). Likewise, z may be any value, integer or non-integer, between 0.1 and 100. In some embodiments, z may be between approximately 2.5 and 3.5. Additionally CsSnI 3  may be doped or compounded with other materials, such as SnF 2 , in ratios of CsSnI 3 :SnF 2  ranging from 0.1:1 to 100:1, including all values (integer and non-integer) in between. 
     In addition, a thin-coat IFL may comprise a bilayer. Thus, returning to the example wherein the thin-coat IFL comprises a metal-oxide (such as alumina), the thin-coat IFL may comprise TiO 2 -plus-metal-oxide. Such a thin-coat IFL may have a greater ability to resist charge recombination as compared to mesoporous TiO 2  or other active material alone. Furthermore, in forming a TiO 2  layer, a secondary TiO 2  coating is often necessary in order to provide sufficient physical interconnection of TiO 2  particles, according to some embodiments of the present disclosure. Coating a bilayer thin-coat IFL onto mesoporous TiO 2  (or other mesoporous active material) may comprise a combination of coating using a compound comprising both metal oxide and TiCl 4 , resulting in an bilayer thin-coat IFL comprising a combination of metal-oxide and secondary TiO 2  coating, which may provide performance improvements over use of either material on its own. 
     In some embodiments, the IFL may comprise a titanate. A titanate according to some embodiments may be of the general formula M′TiO 3 , where: M′ comprises any 2+ cation. In some embodiments, M′ may comprise a cationic form of Be, Mg, Ca, Sr, Ba, Ni, Zn, Cd, Hg, Cu, Pd, Pt, Sn, or Pb. In some embodiments, the IFL may comprise a single species of titanate, which in other embodiments, the IFL may comprise two or more different species of titanates. In one embodiment, the titanate has the formula SrTiO 3 . In another embodiment, the titanate may have the formula BaTiO 3 . In yet another embodiment, the titanate may have the formula CaTiO 3 . 
     By way of explanation, and without implying any limitation, titanates have a perovskite crystalline structure and strongly seed the MAPbI 3  growth conversion process. Titanates generally also meet other IFL requirements, such as ferroelectric behavior, sufficient charge carrier mobility, optical transparency, matched energy levels, and high dielectric constant. 
     Any interfacial material discussed herein may further comprise doped compositions. To modify the characteristics (e.g., electrical, optical, mechanical) of an interfacial material, a stoichiometric or non-stoichiometric material may be doped with one or more elements (e.g., Na, Y, Mg, N, P) in amounts ranging from as little as 1 ppb to 50 mol %. Some examples of interfacial materials include: NiO, TiO 2 , SrTiO 3 , Al 2 O 3 , ZrO 2 , WO 3 , V 2 O 5 , MO 3 , ZnO, graphene, and carbon black. Examples of possible dopants for these interfacial materials include: Be, Mg, Ca, Sr, Ba, Sc, Y, Nb, Ti, Fe, Co, Ni, Cu, Ga, Sn, In, B, N, P, C, S, As, a halide, a pseudohalide (e.g., cyanide, cyanate, isocyanate, fulminate, thiocyanate, isothiocyanate, azide, tetracarbonylcobaltate, carbamoyldicyanomethanide, dicyanonitrosomethanide, dicyanamide, and tricyanomethanide), and Al in any of its oxidation states. References herein to doped interfacial materials are not intended to limit the ratios of component elements in interfacial material compounds. 
       FIG. 10  is a stylized diagram of a perovskite material device  4400  according to some embodiments. Although various components of the device  4400  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 10  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  4400  includes first and second substrates  4401  and  4407 . A first electrode (ITO)  4402  is disposed upon an inner surface of the first substrate  4401 , and a second electrode (Ag)  4406  is disposed on an inner surface of the second substrate  4407 . An active layer  4450  is sandwiched between the two electrodes  4402  and  4406 . The active layer  4450  includes a first IFL (e.g., SrTiO 3 )  4403 , a photoactive material (e.g., MAPbI 3 )  4404 , and a charge transport layer (e.g., Spiro-OMeTAD)  4405 . 
     The thin-coat IFLs and methods of coating them onto TiO 2  previously discussed may, in some embodiments, be employed in DSSCs comprising liquid electrolytes. Thus, returning to the example of a thin-coat IFL and referring back to  FIG. 1  for an example, the DSSC of  FIG. 1  could further comprise a thin-coat IFL as described above coated onto the mesoporous layer  1505  (that is, the thin-coat IFL would be inserted between mesoporous layer  1505  and dye  1504 ). 
     In one embodiment, a perovskite material device may be formulated by casting PbI 2  onto a SrTiO 3 -coated ITO substrate. The may PbI 2  be converted to MAPbI 3  by a dipping process. This process is described in greater detail below. This conversion process is more complete (as observed by optical spectroscopy) as compared to the preparation of the substrate without SrTiO 3 . 
     In some embodiments, the thin-coat IFLs previously discussed in the context of DSSCs may be used in any interfacial layer of a semiconductor device such as a PV (e.g., a hybrid PV or other PV), field-effect transistor, light-emitting diode, non-linear optical device, memristor, capacitor, rectifier, rectifying antenna, etc. Furthermore, thin-coat IFLs of some embodiments may be employed in any of various devices in combination with other compounds discussed in the present disclosure, including but not limited to any one or more of the following of various embodiments of the present disclosure: solid hole-transport material such as active material and additives (such as, in some embodiments, chenodeoxycholic acid or 1,8-diiodooctane). 
     In some embodiments, multiple IFLs made from different materials may be arranged adjacent to each other to form a composite IFL. This configuration may involve two different IFLs, three different IFLs, or an even greater number of different IFLs. The resulting multi-layer IFL or composite IFL may be used in lieu of a single-material IFL. For example, a composite IFL may be used as IFL  2626  and/or as IFL  2627  in cell  2610 , shown in the example of  FIG. 4 . While the composite IFL differs from a single-material IFL, the assembly of a perovskite material PV cell having multi-layer IFLs is not substantially different than the assembly of a perovskite material PV cell having only single-material IFLs. 
     Generally, the composite IFL may be made using any of the materials discussed herein as suitable for an IFL. In one embodiment, the IFL comprises a layer of Al 2 O 3  and a layer of ZnO or M:ZnO (doped ZnO, e.g., Be:ZnO, Mg:ZnO, Ca:ZnO, Sr:ZnO, Ba:ZnO, Sc:ZnO, Y:ZnO, Nb:ZnO). In an embodiment, the IFL comprises a layer of ZrO 2  and a layer of ZnO or M:ZnO. In certain embodiments, the IFL comprises multiple layers. In some embodiments, a multi-layer IFL generally has a conductor layer, a dielectric layer, and a semi-conductor layer. In particular embodiments the layers may repeat, for example, a conductor layer, a dielectric layer, a semi-conductor layer, a dielectric layer, and a semi-conductor layer. Examples of multi-layer IFLs include an IFL having an ITO layer, an Al 2 O 3  layer, a ZnO layer, and a second Al 2 O 3  layer; an IFL having an ITO layer, an Al 2 O 3  layer, a ZnO layer, a second Al 2 O 3  layer, and a second ZnO layer; an IFL having an ITO layer, an Al 2 O 3  layer, a ZnO layer, a second Al 2 O 3  layer, a second ZnO layer, and a third Al 2 O 3  layer; and IFLs having as many layers as necessary to achieve the desired performance characteristics. As discussed previously, references to certain stoichiometric ratios are not intended to limit the ratios of component elements in IFL layers according to various embodiments. 
     Arranging two or more adjacent IFLs as a composite IFL may outperform a single IFL in perovskite material PV cells where attributes from each IFL material may be leveraged in a single IFL. For example, in the architecture having an ITO layer, an Al 2 O 3  layer, and a ZnO layer, where ITO is a conducting electrode, Al 2 O 3  is a dielectric material and ZnO is a n-type semiconductor, ZnO acts as an electron acceptor with well performing electron transport properties (e.g., mobility). Additionally, Al 2 O 3  is a physically robust material that adheres well to ITO, homogenizes the surface by capping surface defects (e.g., charge traps), and improves device diode characteristics through suppression of dark current. 
       FIG. 11  is a stylized diagram of a perovskite material device  4500  according to some embodiments. Although various components of the device  4500  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 11  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  4500  includes first and second substrates  4501  and  4508 . A first electrode (e.g., ITO)  4502  is disposed upon an inner surface of the first substrate  4501 , and a second electrode (e.g., Ag)  4507  is disposed on an inner surface of the second substrate  4508 . An active layer  4550  is sandwiched between the two electrodes  4502  and  4507 . The active layer  4550  includes a composite IFL comprising a first IFL (e.g., Al 2 O 3 )  4503  and a second IFL (e.g., ZnO)  4504 , a photoactive material (e.g., MAPbI 3 )  4505 , and a charge transport layer (e.g., Spiro-OMeTAD)  4506 . 
       FIGS. 13-20  are stylized diagrams of perovskite material devices according to some embodiments. Although various components of the devices are illustrated as discrete layers comprising contiguous material, it should be understood that  FIGS. 13-18  are stylized diagrams; thus, embodiments in accordance with them may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The example devices include layers and materials described throughout this disclosure. The devices may include a substrate layer (e.g., glass), electrode layers (e.g., ITO, Ag), interfacial layers, which may be composite IFLs (e.g., ZnO, Al 2 O 3 , Y:ZnO, and/or Nb:ZnO), a photoactive material (e.g. MAPbI 3 , FAPbI 3 , 5-AVA.HCl: MAPbI 3 , and/or CHP: MAPbI 3 ), and a charge transport layer (e.g., Spiro-OMeTAD, PCDTBT, TFB, TPD, PTB7, F8BT, PPV, MDMO-PPV, MEH-PPV, and/or P3HT). 
       FIG. 13  is a stylized diagram of a perovskite material device  6100  according to some embodiments. Although various components of the device  6100  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 13  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6100  includes a substrate (e.g., Glass)  6101 . A first electrode (e.g., ITO)  6102  is disposed upon an inner surface of the substrate  6101 , and a second electrode (e.g., Ag)  6107  is disposed on top of an active layer  6150  that is sandwiched between the two electrodes  6102  and  6107 . The active layer  6150  includes a composite IFL comprising a first IFL (e.g., Al 2 O 3 )  6103  and a second IFL (e.g., ZnO)  6104 , a photoactive material (e.g., MAPbI 3 )  6105 , and a charge transport layer (e.g., Spiro-OMeTAD)  6106 . 
       FIG. 14  is a stylized diagram of a perovskite material device  6200  according to some embodiments. Although various components of the device  6200  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 14  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6200  includes a substrate (e.g., Glass)  6201 . A first electrode (e.g., ITO)  6202  is disposed upon an inner surface of the substrate  6201 , and a second electrode (e.g., Ag)  6206  is disposed on top of an active layer  6250  that is sandwiched between the two electrodes  6202  and  6206 . The active layer  6250  includes an IFL (e.g., Y:ZnO)  6203 , a photoactive material (e.g., MAPbI 3 )  6204 , and a charge transport layer (e.g., P3HT)  6205 . 
       FIG. 15  is a stylized diagram of a perovskite material device  6300  according to some embodiments. Although various components of the device  6300  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 15  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6300  includes a substrate (e.g., Glass)  6301 . A first electrode (e.g., ITO)  6302  is disposed upon an inner surface of the substrate  6301 , and a second electrode (e.g., Ag)  6309  is disposed on top of an active layer  6350  that is sandwiched between the two electrodes  6302  and  6309 . The active layer  6350  includes a composite IFL comprising a first IFL (e.g., Al 2 O 3 )  6303 , a second IFL (e.g., ZnO)  6304 , a third IFL (e.g., Al 2 O 3 )  6305 , and a fourth IFL (e.g., ZnO)  6306 , a photoactive material (e.g., MAPbI 3 )  6307 , and a charge transport layer (e.g., PCDTBT)  6308 . 
       FIG. 16  is a stylized diagram of a perovskite material device  6400  according to some embodiments. Although various components of the device  6400  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 16  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6400  includes a substrate (e.g., Glass)  6401 . A first electrode (e.g., ITO)  6402  is disposed upon an inner surface of the substrate  6401 , and a second electrode (e.g., Ag)  6409  is disposed on top of an active layer  6450  that is sandwiched between the two electrodes  6402  and  6409 . The active layer  6450  includes a composite IFL comprising a first IFL (e.g., Al 2 O 3 )  6403 , a second IFL (e.g., ZnO)  6404 , a third IFL (e.g., Al 2 O 3 )  6405 , and a fourth IFL (e.g., ZnO)  6406 , a photoactive material (e.g., 5-AVA.HCL:MAPbI 3 )  6407 , and a charge transport layer (e.g., PCDTBT)  6408 . 
       FIG. 17  is a stylized diagram of a perovskite material device  6500  according to some embodiments. Although various components of the device  6500  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 17  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6500  includes a substrate (e.g., Glass)  6501 . A first electrode (e.g., ITO)  6502  is disposed upon an inner surface of the substrate  6501 , and a second electrode (e.g., Ag)  6506  is disposed on top of an active layer  6550  that is sandwiched between the two electrodes  6502  and  6506 . The active layer  6550  includes an IFL (e.g., Nb:ZnO)  6503 , a photoactive material (e.g., FAPbI 3 )  6504 , and a charge transport layer (e.g., P3HT)  6505 . 
       FIG. 18  is a stylized diagram of a perovskite material device  6600  according to some embodiments. Although various components of the device  6600  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 18  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6600  includes a substrate (e.g., Glass)  6601 . A first electrode (e.g., ITO)  6602  is disposed upon an inner surface of the substrate  6601 , and a second electrode (e.g., Ag)  6606  is disposed on top of an active layer  6650  that is sandwiched between the two electrodes  6602  and  6606 . The active layer  6650  includes an IFL (e.g., Y:ZnO)  6603 , a photoactive material (e.g., CHP;MAPbI 3 )  6604 , and a charge transport layer (e.g., P3HT)  6605 . 
       FIG. 19  is a stylized diagram of a perovskite material device  6700  according to some embodiments. Although various components of the device  6700  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 19  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6700  includes a substrate (e.g., Glass)  6701 . A first electrode (e.g., ITO)  6702  is disposed upon an inner surface of the substrate  6701 , and a second electrode (e.g., Al)  6707  is disposed on top of an active layer  6750  that is sandwiched between the two electrodes  6702  and  6707 . The active layer  6750  includes an IFL (e.g., SrTiO 3 )  6703  a photoactive material (e.g., FAPbI 3 )  6704 , a first charge transport layer (e.g., P3HT)  6705 , and a second charge transport layer (e.g., MoOx)  6706 . 
       FIG. 20  is a stylized diagram of a perovskite material device  6800  according to some embodiments. Although various components of the device  6800  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 16  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  6800  includes a substrate (e.g., Glass)  6801 . A first electrode (e.g., ITO)  6802  is disposed upon an inner surface of the substrate  6801 , and a second electrode (e.g., Al)  6811  is disposed on top of an active layer  6850  that is sandwiched between the two electrodes  6802  and  6811 . The active layer  6850  includes a composite IFL comprising a first IFL (e.g., Al 2 O 3 )  6803 , a second IFL (e.g., ZnO)  6804 , a third IFL (e.g., Al 2 O 3 )  6805 , a fourth IFL (e.g., ZnO)  6806 , and a fifth IFL (e.g., Al 2 O 3 )  6807 , a photoactive material (e.g., FAPbI 3 )  6808 , a first charge transport layer (e.g., P3HT)  6809 , and a second charge transport layer (e.g., MoOx)  6810 . 
     Perovskite Material 
     A perovskite material may be incorporated into various of one or more aspects of a PV or other device. A perovskite material according to some embodiments may be of the general formula CMX 3 , where: C comprises one or more cations (e.g., an amine, ammonium, a Group 1 metal, a Group 2 metal, and/or other cations or cation-like compounds); M comprises one or more metals (examples including Fe, Co, Ni, Cu, Sn, Pb, Bi, Ge, Ti, and Zr); and X comprises one or more anions. In some embodiments, C may include one or more organic cations. 
     In certain embodiments, C may include an ammonium, an organic cation of the general formula [NR 4 ] +  where the R groups may be the same or different groups. Suitable R groups include, but are not limited to: methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; any alkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic, branched or straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42, z=1-42, X=F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., pyridine, pyrrole, pyrrolidine, piperidine, tetrahydroquinoline); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (e.g., acetic acid, propanoic acid); and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any alkoxy or group, —OCxHy, where x=0-20, y=1-42. 
     In certain embodiments, C may include a formamidinium, an organic cation of the general formula [R 2 NCRNR 2 ] +  where the R groups may be the same or different groups. Suitable R groups include, but are not limited to: hydrogen, methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; any alkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic, branched or straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42, z=1-42, X=F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., imidazole, benzimidazole, dihydropyrimidine, (azolidinylidenemethyl)pyrrolidine, triazole); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (acetic acid, propanoic acid) and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any alkoxy or group, —OCxHy, where x=0-20, y=1-42. 
     
       
         
         
             
             
         
       
     
     Formula 1 illustrates the structure of a formamidinium cation having the general formula of [R 2 NCRNR 2 ] +  as described above. Formula 2 illustrates examples structures of several formamidinium cations that may serve as a cation “C” in a perovskite material. 
     
       
         
         
             
             
         
       
     
     In certain embodiments, C may include a guanidinium, an organic cation of the general formula [(R 2 N) 2 C═NR 2 ] +  where the R groups may be the same or different groups. Suitable R groups include, but are not limited to: hydrogen, methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; any alkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic, branched or straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42, z=1-42, X=F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., octahydropyrimido[1,2-a]pyrimidine, pyrimido[1,2-a]pyrimidine, hexahydroimidazo[1,2-a]imidazole, hexahydropyrimidin-2-imine); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (acetic acid, propanoic acid) and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any alkoxy or group, —OCxHy, where x=0-20, y=1-42. 
     
       
         
         
             
             
         
       
     
     Formula 3 illustrates the structure of a guanidinium cation having the general formula of [(R 2 N) 2 C═NR 2 ] +  as described above. Formula 4 illustrates examples of structures of several guanidinium cations that may serve as a cation “C” in a perovskite material. 
     
       
         
         
             
             
         
       
     
     In certain embodiments, C may include an ethene tetramine cation, an organic cation of the general formula [(R 2 N) 2 C═C(NR 2 ) 2 ] +  where the R groups may be the same or different groups. Suitable R groups include, but are not limited to: hydrogen, methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; any alkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic, branched or straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42, z=1-42, X═F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., 2-hexahydropyrimidin-2-ylidenehexahydropyrimidine, octahydropyrazino[2,3-b]pyrazine, pyrazino[2,3-b]pyrazine, quinoxalino[2,3-b]quinoxaline); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (acetic acid, propanoic acid) and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any aikoxy or group, —OCxHy, where x=0-20, y=1-42. 
     
       
         
         
             
             
         
       
     
     Formula 5 illustrates the structure of an ethene tetramine cation having the general formula of [(R 2 N) 2 C═C(NR 2 ) 2 ] +  as described above. Formula 6 illustrates examples of structures of several ethene tetramine ions that may serve as a cation “C” in a perovskite material. 
     
       
         
         
             
             
         
       
     
     In certain embodiments, C may include an imidazolium cation, an aromatic, cyclic organic cation of the general formula [CRNRCRNRCR] +  where the R groups may be the same or different groups. Suitable R groups may include, but are not limited to: hydrogen, methyl, ethyl, propyl, butyl, pentyl group or isomer thereof; any alkane, alkene, or alkyne CxHy, where x=1-20, y=1-42, cyclic, branched or straight-chain; alkyl halides, CxHyXz, x=1-20, y=0-42, z=1-42, X=F, Cl, Br, or I; any aromatic group (e.g., phenyl, alkylphenl, alkoxyphenyl, pyridine, naphthalene); cyclic complexes where at least one nitrogen is contained within the ring (e.g., 2-hexahydropyrimidin-2-ylidenehexahydropyrimidine, octahydropyrazino[2,3-b]pyrazine, pyrazino[2,3-b]pyrazine, quinoxalino[2,3-b]quinoxaline); any sulfur-containing group (e.g., sulfoxide, thiol, alkyl sulfide); any nitrogen-containing group (nitroxide, amine); any phosphorous containing group (phosphate); any boron-containing group (e.g., boronic acid); any organic acid (acetic acid, propanoic acid) and ester or amide derivatives thereof; any amino acid (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives; any silicon containing group (e.g., siloxane); and any alkoxy or group, —OCxHy, where x=0-20, y=1-42. 
     
       
         
         
             
             
         
       
     
     In some embodiments, X may include one or more halides. In certain embodiments, X may instead or in addition include a Group 16 anion. In certain embodiments, the Group 16 anion may be sulfide or selenide. In certain embodiments, X may instead or in addition include one or more a pseudohalides (e.g., cyanide, cyanate, isocyanate, fulminate, thiocyanate, isothiocyanate, azide, tetracarbonylcobaltate, carbamoyldicyanomethanide, dicyanonitrosomethanide, dicyanamide, and tricyanomethanide). In some embodiments, each organic cation C may be larger than each metal M, and each anion X may be capable of bonding with both a cation C and a metal M. Examples of perovskite materials according to various embodiments include CsSnI 3  (previously discussed herein) and Cs x Sn y I z  (with x, y, and z varying in accordance with the previous discussion). Other examples include compounds of the general formula CsSnX 3 , where X may be any one or more of: I 3 , I 2.95 F 0.05 ; I 2 Cl; ICl 2 ; and Cl 3 . In other embodiments, X may comprise any one or more of I, Cl, F, and Br in amounts such that the total ratio of X as compared to Cs and Sn results in the general stoichiometry of CsSnX 3 . In some embodiments, the combined stoichiometry of the elements that constitute X may follow the same rules as I z  as previously discussed with respect to Cs x Sn y I z . Yet other examples include compounds of the general formula RNH 3 PbX 3 , where R may be C n H 2n+1 , with n ranging from 0-10, and X may include any one or more of F, Cl, Br, and I in amounts such that the total ratio of X as compared to the cation RNH 3  and metal Pb results in the general stoichiometry of RNH 3 PbX 3 . Further, some specific examples of R include H, alkyl chains (e.g., CH 3 , CH 3 CH 2 , CH 3 CH 2 CH 2 , and so on), and amino acids (e.g., glycine, cysteine, proline, glutamic acid, arginine, serine, histindine, 5-ammoniumvaleric acid) including alpha, beta, gamma, and greater derivatives. 
     Composite Perovskite Material Device Design 
     In some embodiments, the present disclosure may provide composite design of PV and other similar devices (e.g., batteries, hybrid PV batteries, FETs, LEDs etc.) including one or more perovskite materials. For example, one or more perovskite materials may serve as either or both of first and second active material of some embodiments (e.g., active materials  2810  and  2815  of  FIG. 5 ). In more general terms, some embodiments of the present disclosure provide PV or other devices having an active layer comprising one or more perovskite materials. In such embodiments, perovskite material (that is, material including any one or more perovskite materials(s)) may be employed in active layers of various architectures. Furthermore, perovskite material may serve the function(s) of any one or more components of an active layer (e.g., charge transport material, mesoporous material, photoactive material, and/or interfacial material, each of which is discussed in greater detail below). In some embodiments, the same perovskite materials may serve multiple such functions, although in other embodiments, a plurality of perovskite materials may be included in a device, each perovskite material serving one or more such functions. In certain embodiments, whatever role a perovskite material may serve, it may be prepared and/or present in a device in various states. For example, it may be substantially solid in some embodiments. In other embodiments, it may be a solution (e.g., perovskite material may be dissolved in liquid and present in said liquid in its individual ionic subspecies); or it may be a suspension (e.g., of perovskite material particles). A solution or suspension may be coated or otherwise deposited within a device (e.g., on another component of the device such as a mesoporous, interfacial, charge transport, photoactive, or other layer, and/or on an electrode). Perovskite materials in some embodiments may be formed in situ on a surface of another component of a device (e.g., by vapor deposition as a thin-film solid). Any other suitable means of forming a solid or liquid layer comprising perovskite material may be employed. 
     In general, a perovskite material device may include a first electrode, a second electrode, and an active layer comprising a perovskite material, the active layer disposed at least partially between the first and second electrodes. In some embodiments, the first electrode may be one of an anode and a cathode, and the second electrode may be the other of an anode and cathode. An active layer according to certain embodiments may include any one or more active layer components, including any one or more of: charge transport material; liquid electrolyte; mesoporous material; photoactive material (e.g., a dye, silicon, cadmium telluride, cadmium sulfide, cadmium selenide, copper indium gallium selenide, gallium arsenide, germanium indium phosphide, semiconducting polymers, other photoactive materials)); and interfacial material. Any one or more of these active layer components may include one or more perovskite materials. In some embodiments, some or all of the active layer components may be in whole or in part arranged in sub-layers. For example, the active layer may comprise any one or more of: an interfacial layer including interfacial material; a mesoporous layer including mesoporous material; and a charge transport layer including charge transport material. In some embodiments, photoactive material such as a dye may be coated on, or otherwise disposed on, any one or more of these layers. In certain embodiments, any one or more layers may be coated with a liquid electrolyte. Further, an interfacial layer may be included between any two or more other layers of an active layer according to some embodiments, and/or between a layer and a coating (such as between a dye and a mesoporous layer), and/or between two coatings (such as between a liquid electrolyte and a dye), and/or between an active layer component and an electrode. Reference to layers herein may include either a final arrangement (e.g., substantially discrete portions of each material separately definable within the device), and/or reference to a layer may mean arrangement during construction of a device, notwithstanding the possibility of subsequent intermixing of material(s) in each layer. Layers may in some embodiments be discrete and comprise substantially contiguous material (e.g., layers may be as stylistically illustrated in  FIG. 1 ). In other embodiments, layers may be substantially intermixed (as in the case of, e.g., BHJ, hybrid, and some DSSC cells), an example of which is shown by first and second active material  2618  and  2620  within photoactive layer  2616  in  FIG. 4 . In some embodiments, a device may comprise a mixture of these two kinds of layers, as is also shown by the device of  FIG. 4 , which contains discrete contiguous layers  2627 ,  2626 , and  2622 , in addition to a photoactive layer  2616  comprising intermixed layers of first and second active material  2618  and  2620 . In any case, any two or more layers of whatever kind may in certain embodiments be disposed adjacent to each other (and/or intermixedly with each other) in such a way as to achieve a high contact surface area. In certain embodiments, a layer comprising perovskite material may be disposed adjacent to one or more other layers so as to achieve high contact surface area (e.g., where a perovskite material exhibits low charge mobility). In other embodiments, high contact surface area may not be necessary (e.g., where a perovskite material exhibits high charge mobility). 
     A perovskite material device according to some embodiments may optionally include one or more substrates. In some embodiments, either or both of the first and second electrode may be coated or otherwise disposed upon a substrate, such that the electrode is disposed substantially between a substrate and the active layer. The materials of composition of devices (e.g., substrate, electrode, active layer and/or active layer components) may in whole or in part be either rigid or flexible in various embodiments. In some embodiments, an electrode may act as a substrate, thereby negating the need for a separate substrate. 
     Furthermore, a perovskite material device according to certain embodiments may optionally include light-harvesting material (e.g., in a light-harvesting layer, such as Light Harvesting Layer  1601  as depicted in the example PV represented in  FIG. 2 ). In addition, a perovskite material device may include any one or more additives, such as any one or more of the additives discussed above with respect to some embodiments of the present disclosure. 
     Description of some of the various materials that may be included in a perovskite material device will be made in part with reference to  FIG. 7 .  FIG. 7  is a stylized diagram of a perovskite material device  3900  according to some embodiments. Although various components of the device  3900  are illustrated as discrete layers comprising contiguous material, it should be understood that  FIG. 7  is a stylized diagram; thus, embodiments in accordance with it may include such discrete layers, and/or substantially intermixed, non-contiguous layers, consistent with the usage of “layers” previously discussed herein. The device  3900  includes first and second substrates  3901  and  3913 . A first electrode  3902  is disposed upon an inner surface of the first substrate  3901 , and a second electrode  3912  is disposed on an inner surface of the second substrate  3913 . An active layer  3950  is sandwiched between the two electrodes  3902  and  3912 . The active layer  3950  includes a mesoporous layer  3904 ; first and second photoactive materials  3906  and  3908 ; a charge transport layer  3910 , and several interfacial layers.  FIG. 7  furthermore illustrates an example device  3900  according to embodiments wherein sub-layers of the active layer  3950  are separated by the interfacial layers, and further wherein interfacial layers are disposed upon each electrode  3902  and  3912 . In particular, second, third, and fourth interfacial layers  3905 ,  3907 , and  3909  are respectively disposed between each of the mesoporous layer  3904 , first photoactive material  3906 , second photoactive material  3908 , and charge transport layer  3910 . First and fifth interfacial layers  3903  and  3911  are respectively disposed between (i) the first electrode  3902  and mesoporous layer  3904 ; and (ii) the charge transport layer  3910  and second electrode  3912 . Thus, the architecture of the example device depicted in  FIG. 7  may be characterized as: substrate-electrode-active layer-electrode-substrate. The architecture of the active layer  3950  may be characterized as: interfacial layer-mesoporous layer-interfacial layer-photoactive material-interfacial layer-photoactive material-interfacial layer-charge transport layer-interfacial layer. As noted previously, in some embodiments, interfacial layers need not be present; or, one or more interfacial layers may be included only between certain, but not all, components of an active layer and/or components of a device. 
     A substrate, such as either or both of first and second substrates  3901  and  3913 , may be flexible or rigid. If two substrates are included, at least one should be transparent or translucent to electromagnetic (EM) radiation (such as, e.g., UV, visible, or IR radiation). If one substrate is included, it may be similarly transparent or translucent, although it need not be, so long as a portion of the device permits EM radiation to contact the active layer  3950 . Suitable substrate materials include any one or more of: glass; sapphire; magnesium oxide (MgO); mica; polymers (e.g., PET, PEG, polypropylene, polyethylene, etc.); ceramics; fabrics (e.g., cotton, silk, wool); wood; drywall; metal; and combinations thereof. 
     As previously noted, an electrode (e.g., one of electrodes  3902  and  3912  of  FIG. 7 ) may be either an anode or a cathode. In some embodiments, one electrode may function as a cathode, and the other may function as an anode. Either or both electrodes  3902  and  3912  may be coupled to leads, cables, wires, or other means enabling charge transport to and/or from the device  3900 . An electrode may constitute any conductive material, and at least one electrode should be transparent or translucent to EM radiation, and/or be arranged in a manner that allows EM radiation to contact at least a portion of the active layer  3950 . Suitable electrode materials may include any one or more of: indium tin oxide or tin-doped indium oxide (ITO); fluorine-doped tin oxide (FTO); cadmium oxide (CdO); zinc indium tin oxide (ZITO); aluminum zinc oxide (AZO); aluminum (Al); gold (Au); calcium (Ca); magnesium (Mg); titanium (Ti); steel; carbon (and allotropes thereof); and combinations thereof. 
     Mesoporous material (e.g., the material included in mesoporous layer  3904  of  FIG. 7 ) may include any pore-containing material. In some embodiments, the pores may have diameters ranging from about 1 to about 100 nm; in other embodiments, pore diameter may range from about 2 to about 50 nm. Suitable mesoporous material includes any one or more of: any interfacial material and/or mesoporous material discussed elsewhere herein; aluminum (Al); bismuth (Bi); indium (In); molybdenum (Mo); niobium (Nb); nickel (Ni); silicon (Si); titanium (Ti); vanadium (V); zinc (Zn); zirconium (Zr); an oxide of any one or more of the foregoing metals (e.g., alumina, ceria, titania, zinc oxide, zircona, etc.); a sulfide of any one or more of the foregoing metals; a nitride of any one or more of the foregoing metals; and combinations thereof. 
     Photoactive material (e.g., first or second photoactive material  3906  or  3908  of  FIG. 7 ) may comprise any photoactive compound, such as any one or more of silicon (in some instances, single-crystalline silicon), cadmium telluride, cadmium sulfide, cadmium selenide, copper indium gallium selenide, gallium arsenide, germanium indium phosphide, one or more semiconducting polymers, and combinations thereof. In certain embodiments, photoactive material may instead or in addition comprise a dye (e.g., N719, N3, other ruthenium-based dyes). In some embodiments, a dye (of whatever composition) may be coated onto another layer (e.g., a mesoporous layer and/or an interfacial layer). In some embodiments, photoactive material may include one or more perovskite materials. Perovskite-material-containing photoactive substance may be of a solid form, or in some embodiments it may take the form of a dye that includes a suspension or solution comprising perovskite material. Such a solution or suspension may be coated onto other device components in a manner similar to other dyes. In some embodiments, solid perovskite-containing material may be deposited by any suitable means (e.g., vapor deposition, solution deposition, direct placement of solid material, etc.). Devices according to various embodiments may include one, two, three, or more photoactive compounds (e.g., one, two, three, or more perovskite materials, dyes, or combinations thereof). In certain embodiments including multiple dyes or other photoactive materials, each of the two or more dyes or other photoactive materials may be separated by one or more interfacial layers. In some embodiments, multiple dyes and/or photoactive compounds may be at least in part intermixed. 
     Charge transport material (e.g., charge transport material of charge transport layer  3910  in  FIG. 7 ) may include solid-state charge transport material (i.e., a colloquially labeled solid-state electrolyte), or it may include a liquid electrolyte and/or ionic liquid. Any of the liquid electrolyte, ionic liquid, and solid-state charge transport material may be referred to as charge transport material. As used herein, “charge transport material” refers to any material, solid, liquid, or otherwise, capable of collecting charge carriers and/or transporting charge carriers. For instance, in PV devices according to some embodiments, a charge transport material may be capable of transporting charge carriers to an electrode. Charge carriers may include holes (the transport of which could make the charge transport material just as properly labeled “hole transport material”) and electrons. Holes may be transported toward an anode, and electrons toward a cathode, depending upon placement of the charge transport material in relation to either a cathode or anode in a PV or other device. Suitable examples of charge transport material according to some embodiments may include any one or more of: perovskite material; I − /I 3   − ; Co complexes; polythiophenes (e.g., poly(3-hexylthiophene) and derivatives thereof, or P3HT); carbazole-based copolymers such as polyheptadecanylcarbazole dithienylbenzothiadiazole and derivatives thereof (e.g., PCDTBT); other copolymers such as polycyclopentadithiophene-benzothiadiazole and derivatives thereof (e.g., PCPDTBT), polybenzodithiophenyl-thienothiophenediyl and derivatives thereof (e.g., PTB6, PTB7, PTB7-th, PCE-10); poly(triaryl amine) compounds and derivatives thereof (e.g., PTAA); Spiro-OMeTAD; polyphenylene vinylenes and derivatives thereof (e.g, MDMO-PPV, MEH-PPV); fullerenes and/or fullerene derivatives (e.g., C60, PCBM); and combinations thereof. In certain embodiments, charge transport material may include any material, solid or liquid, capable of collecting charge carriers (electrons or holes), and/or capable of transporting charge carriers. Charge transport material of some embodiments therefore may be n- or p-type active and/or semi-conducting material. Charge transport material may be disposed proximate to one of the electrodes of a device. It may in some embodiments be disposed adjacent to an electrode, although in other embodiments an interfacial layer may be disposed between the charge transport material and an electrode (as shown, e.g., in  FIG. 7  with the fifth interfacial layer  3911 ). In certain embodiments, the type of charge transport material may be selected based upon the electrode to which it is proximate. For example, if the charge transport material collects and/or transports holes, it may be proximate to an anode so as to transport holes to the anode. However, the charge transport material may instead be placed proximate to a cathode, and be selected or constructed so as to transport electrons to the cathode. 
     As previously noted, devices according to various embodiments may optionally include an interfacial layer between any two other layers and/or materials, although devices according to some embodiments need not contain any interfacial layers. Thus, for example, a perovskite material device may contain zero, one, two, three, four, five, or more interfacial layers (such as the example device of  FIG. 7 , which contains five interfacial layers  3903 ,  3905 ,  3907 ,  3909 , and  3911 ). An interfacial layer may include a thin-coat interfacial layer in accordance with embodiments previously discussed herein (e.g., comprising alumina and/or other metal-oxide particles, and/or a titania/metal-oxide bilayer, and/or other compounds in accordance with thin-coat interfacial layers as discussed elsewhere herein). An interfacial layer according to some embodiments may include any suitable material for enhancing charge transport and/or collection between two layers or materials; it may also help prevent or reduce the likelihood of charge recombination once a charge has been transported away from one of the materials adjacent to the interfacial layer. Suitable interfacial materials may include any one or more of: any mesoporous material and/or interfacial material discussed elsewhere herein; Al; Bi; Co; Cu; Fe; In; Mn; Mo; Ni; platinum (Pt); Si; Sn; Ta; Ti; V; W; Nb; Zn; Zr; oxides of any of the foregoing metals (e.g., alumina, silica, titania); a sulfide of any of the foregoing metals; a nitride of any of the foregoing metals; functionalized or non-functionalized alkyl silyl groups; graphite; graphene; fullerenes; carbon nanotubes; and combinations thereof (including, in some embodiments, bilayers of combined materials). In some embodiments, an interfacial layer may include perovskite material. 
     A device according to the stylized representation of  FIG. 7  may in some embodiments be a PV, such as a DSSC, BHJ, or hybrid solar cell. In some embodiments, devices according to  FIG. 7  may constitute parallel or serial multi-cell PVs, batteries, hybrid PV batteries, FETs, LEDS, and/or any other device discussed herein. For example, a BHJ of some embodiments may include two electrodes corresponding to electrodes  3902  and  3912 , and an active layer comprising at least two materials in a heterojunction interface (e.g., any two of the materials and/or layers of active layer  3950 ). In certain embodiments, other devices (such as hybrid PV batteries, parallel or serial multi-cell PVs, etc.) may comprise an active layer including a perovskite material, corresponding to active layer  3950  of  FIG. 7 . In short, the stylized nature of the depiction of the example device of  FIG. 7  should in no way limit the peimissible structure or architecture of devices of various embodiments in accordance with  FIG. 7 . 
     Additional, more specific, example embodiments of perovskite devices will be discussed in terms of further stylized depictions of example devices. The stylized nature of these depictions,  FIGS. 8-18 , similarly is not intended to restrict the type of device which may in some embodiments be constructed in accordance with any one or more of  FIGS. 8-18 . That is, the architectures exhibited in  FIGS. 8-18  may be adapted so as to provide the BHJs, batteries, FETs, hybrid PV batteries, serial multi-cell PVs, parallel multi-cell PVs and other similar devices of other embodiments of the present disclosure, in accordance with any suitable means (including both those expressly discussed elsewhere herein, and other suitable means, which will be apparent to those skilled in the art with the benefit of this disclosure). 
       FIG. 8  depicts an example device  4100  in accordance with various embodiments. The device  4100  illustrates embodiments including first and second glass substrates  4101  and  4109 . Each glass substrate has an FTO electrode disposed upon its inner surface (first electrode  4102  and second electrode  4108 , respectively), and each electrode has an interfacial layer deposited upon its inner surface: TiO 2  first interfacial layer  4103  is deposited upon first electrode  4102 , and Pt second interfacial layer  4107  is deposited upon second electrode  4108 . Sandwiched between the two interfacial layers are: a mesoporous layer  4104  (comprising TiO 2 ); photoactive material  4105  (comprising the perovskite material MAPbI 3 ); and a charge transport layer  4106  (here comprising CsSnI 3 ). 
       FIG. 9  depicts an example device  4300  that omits a mesoporous layer. The device  4300  includes a perovskite material photoactive compound  4304  (comprising MAPbI 3 ) sandwiched between first and second interfacial layers  4303  and  4305  (comprising titania and alumina, respectively). The titania interfacial layer  4303  is coated upon an FTO first electrode  4302 , which in turn is disposed on an inner surface of a glass substrate  4301 . The spiro-OMeTAD charge transport layer  4306  is coated upon an alumina interfacial layer  4305  and disposed on an inner surface of a gold second electrode  4307 . 
     As will be apparent to one of ordinary skill in the art with the benefit of this disclosure, various other embodiments are possible, such as a device with multiple photoactive layers (as exemplified by photoactive layers  3906  and  3908  of the example device of  FIG. 7 ). In some embodiments, as discussed above, each photoactive layer may be separated by an interfacial layer (as shown by third interfacial layer  3907  in  FIG. 7 ). Furthermore, a mesoporous layer may be disposed upon an electrode such as is illustrated in  FIG. 7  by mesoporous layer  3904  being disposed upon first electrode  3902 . Although  FIG. 7  depicts an intervening interfacial layer  3903  disposed between the two, in some embodiments a mesoporous layer may be disposed directly on an electrode. 
     Additional Perovskite Material Device Examples 
     Other example perovskite material device architectures will be apparent to those of skill in the art with the benefit of this disclosure. Examples include, but are not limited to, devices containing active layers having any of the following architectures: (1) liquid electrolyte-perovskite material-mesoporous layer; (2) perovskite material-dye-mesoporous layer; (3) first perovskite material-second perovskite material-mesoporous layer; (4) first perovskite material-second perovskite material; (5) first perovskite material-dye-second perovskite material; (6) solid-state charge transport material-perovskite material; (7) solid-state charge transport material-dye-perovskite material-mesoporous layer; (8) solid-state charge transport material-perovskite material-dye-mesoporous layer; (9) solid-state charge transport material-dye-perovskite material-mesoporous layer; and (10) solid-state charge transport material-perovskite material-dye-mesoporous layer. The individual components of each example architecture (e.g., mesoporous layer, charge transport material, etc.) may be in accordance with the discussion above for each component. Furthermore, each example architecture is discussed in more detail below. 
     As a particular example of some of the aforementioned active layers, in some embodiments, an active layer may include a liquid electrolyte, perovskite material, and a mesoporous layer. The active layer of certain of these embodiments may have substantially the architecture: liquid electrolyte-perovskite material-mesoporous layer. Any liquid electrolyte may be suitable; and any mesoporous layer (e.g., TiO 2 ) may be suitable. In some embodiments, the perovskite material may be deposited upon the mesoporous layer, and thereupon coated with the liquid electrolyte. The perovskite material of some such embodiments may act at least in part as a dye (thus, it may be photoactive). 
     In other example embodiments, an active layer may include perovskite material, a dye, and a mesoporous layer. The active layer of certain of these embodiments may have substantially the architecture: perovskite material dye-mesoporous layer. The dye may be coated upon the mesoporous layer and the perovskite material may be disposed upon the dye-coated mesoporous layer. The perovskite material may function as hole-transport material in certain of these embodiments. 
     In yet other example embodiments, an active layer may include first perovskite material, second perovskite material, and a mesoporous layer. The active layer of certain of these embodiments may have substantially the architecture: first perovskite material-second perovskite material-mesoporous layer. The first and second perovskite material may each comprise the same perovskite material(s) or they may comprise different perovskite materials. Either of the first and second perovskite materials may be photoactive (e.g., a first and/or second perovskite material of such embodiments may function at least in part as a dye). 
     In certain example embodiments, an active layer may include first perovskite material and second perovskite material. The active layer of certain of these embodiments may have substantially the architecture: first perovskite material-second perovskite material. The first and second perovskite materials may each comprise the same perovskite material(s) or they may comprise different perovskite materials. Either of the first and second perovskite materials may be photoactive (e.g., a first and/or second perovskite material of such embodiments may function at least in part as a dye). In addition, either of the first and second perovskite materials may be capable of functioning as hole-transport material. In some embodiments, one of the first and second perovskite materials functions as an electron-transport material, and the other of the first and second perovskite materials functions as a dye. In some embodiments, the first and second perovskite materials may be disposed within the active layer in a manner that achieves high interfacial area between the first perovskite material and the second perovskite material, such as in the arrangement shown for first and second active material  2810  and  2815 , respectively, in  FIG. 5  (or as similarly shown by p- and n-type material  2618  and  2620 , respectively, in  FIG. 4 ). 
     In further example embodiments, an active layer may include first perovskite material, a dye, and second perovskite material. The active layer of certain of these embodiments may have substantially the architecture: first perovskite material-dye-second perovskite material. Either of the first and second perovskite materials may function as charge transport material, and the other of the first and second perovskite materials may function as a dye. In some embodiments, both of the first and second perovskite materials may at least in part serve overlapping, similar, and/or identical functions (e.g., both may serve as a dye and/or both may serve as hole-transport material). 
     In some other example embodiments, an active layer may include a solid-state charge transport material and a perovskite material. The active layer of certain of these embodiments may have substantially the architecture: solid-state charge transport material-perovskite material. For example, the perovskite material and solid-state charge transport material may be disposed within the active layer in a manner that achieves high interfacial area, such as in the arrangement shown for first and second active material  2810  and  2815 , respectively, in  FIG. 5  (or as similarly shown by p- and n-type material  2618  and  2620 , respectively, in  FIG. 4 ). 
     In other example embodiments, an active layer may include a solid-state charge transport material, a dye, perovskite material, and a mesoporous layer. The active layer of certain of these embodiments may have substantially the architecture: solid-state charge transport material—dye—perovskite material—mesoporous layer. The active layer of certain other of these embodiments may have substantially the architecture: solid-state charge transport material—perovskite material—dye—mesoporous layer. The perovskite material may in some embodiments serve as a second dye. The perovskite material may in such embodiments increase the breadth of the spectrum of visible light absorbed by a PV or other device including an active layer of such embodiments. In certain embodiments, the perovskite material may also or instead serve as an interfacial layer between the dye and mesoporous layer, and/or between the dye and the charge transport material. 
     In some example embodiments, an active layer may include a liquid electrolyte, a dye, a perovskite material, and a mesoporous layer. The active layer of certain of these embodiments may have substantially the architecture: solid-state charge transport material—dye—perovskite material—mesoporous layer. The active layer of certain other of these embodiments may have substantially the architecture: solid-state charge transport material—perovskite material—dye—mesoporous layer. The perovskite material may serve as photoactive material, an interfacial layer, and/or a combination thereof. 
     Some embodiments provide BHJ PV devices that include perovskite materials. For example, a BHJ of some embodiments may include a photoactive layer (e.g., photoactive layer  2404  of  FIG. 3 ), which may include one or more perovskite materials. The photoactive layer of such a BHJ may also or instead include any one or more of the above-listed example components discussed above with respect to DSSC active layers. Further, in some embodiments, the BHJ photoactive layer may have an architecture according to any one of the example embodiments of DSSC active layers discussed above. 
     In some embodiments, any of the active layers including perovskite materials incorporated into PVs or other devices as discussed herein may further include any of the various additional materials also discussed herein as suitable for inclusion in an active layer. For example, any active layer including perovskite material may further include an interfacial layer according to various embodiments discussed herein (such as, e.g., a thin-coat interfacial layer). By way of further example, an active layer including perovskite material may further include a light harvesting layer, such as Light Harvesting Layer  1601  as depicted in the example PV represented in  FIG. 2 . 
     Formulation of the Perovskite Material Active Layer 
     As discussed earlier, in some embodiments, a perovskite material in the active layer may have the formulation CMX 3-y X′ y  (0≥y≥3), where: C comprises one or more cations (e.g., an amine, ammonium, a Group 1 metal, a Group 2 metal, formamidinium, guanidinium, ethene tetramine and/or other cations or cation-like compounds); M comprises one or more metals (e.g., Fe, Cd, Co, Ni, Cu, Hg, Sn, Pb, Bi, Ge, Ti, Zn, and Zr); and X and X′ comprise one or more anions. In one embodiment, the perovskite material may comprise CPbI 3-y Cl y . In certain embodiments, the perovskite material may be deposited as an active layer in a PV device by, for example, drop casting, spin casting, slot-die printing, screen printing, or ink-jet printing onto a substrate layer using the steps described below. 
     First, a lead halide precursor ink is formed. An amount of lead halide may be massed in a clean, dry vial inside a glove box (i.e., controlled atmosphere box with glove-containing portholes allows for materials manipulation in an air-free environment). Suitable lead halides include, but are not limited to, lead (II) iodide, lead (II) bromide, lead (II) chloride, and lead (II) fluoride. The lead halide may comprise a single species of lead halide or it may comprise a lead halide mixture in a precise ratio. In certain embodiments, the lead halide mixture may comprise any binary, ternary, or quaternary ratio of 0.001-100 mol % of iodide, bromide, chloride, or fluoride. In one embodiment, the lead halide mixture may comprise lead (II) chloride and lead (II) iodide in a ratio of about 10:90 mol:mol. In other embodiments, the lead halide mixture may comprise lead (II) chloride and lead (II) iodide in a ratio of about 5:95, about 7.5:92.5, or about 15:85 mol:mol. 
     Alternatively, other lead salt precursors may be used in conjunction with or in lieu of lead halide salts to form the precursor ink. Suitable precursor salts may comprise any combination of lead (II) or lead(IV) and the following anions: nitrate, nitrite, carboxylate, acetate, formate, oxylate, sulfate, sulfite, thiosulfate, phosphate, tetrafluoroborate, hexafluorophosphate, tetra(perfluorophenyl) borate, hydride, oxide, peroxide, hydroxide, nitride, arsenate, arsenite, perchlorate, carbonate, bicarbonate, chromate, dichromate, iodate, bromate, chlorate, chlorite, hypochlorite, hypobromite, cyanide, cyanate, isocyanate, fulminate, thiocyanate, isothiocyanate, azide, tetracarbonylcobaltate, carbamoyldicyanomethanide, dicyanonitrosomethanide, dicyanamide, tricyanomethanide, amide, and permanganate. 
     The precursor ink may further comprise a lead (II) or lead (IV) salt in mole ratios of 0 to 100% to the following metal ions Fe, Cd, Co, Ni, Cu, Hg, Sn, Pb, Bi, Ge, Ti, Zn, and Zr as a salt of the aforementioned anions. 
     A solvent may then be added to the vial to dissolve the lead solids to form the lead halide precursor ink. Suitable solvents include, but are not limited to, dry N-cyclohexyl-2-pyrrolidone, alkyl-2-pyrrolidone, dimethylformamide, dialkylformamide, dimethylsulfoxide (DMSO), methanol, ethanol, propanol, butanol, tetrahydrofuran, formamide, tert-butylpyridine, pyridine, alkylpyridine, pyrrolidine, chlorobenzene, dichlorobenzene, dichloromethane, chloroform, and combinations thereof. In one embodiment, the lead solids are dissolved in dry dimethylformamide (DMF). The lead solids may be dissolved at a temperature between about 20° C. to about 150° C. In one embodiment, the lead solids are dissolved at about 85° C. The lead solids may be dissolved for as long as necessary to form a solution, which may take place over a time period up to about 72 hours. The resulting solution forms the base of the lead halide precursor ink. In some embodiments, the lead halide precursor ink may have a lead halide concentration between about 0.001M and about 10M. In one embodiment, the lead halide precursor ink has a lead halide concentration of about 1 M. 
     Optionally, certain additives may be added to the lead halide precursor ink to affect the final perovskite crystallinity and stability. In some embodiments, the lead halide precursor ink may further comprise an amino acid (e.g., 5-aminovaleric acid, histidine, glycine, lycine), an amino acid hydrohalide (e.g., 5-amino valeric acid hydrochloride), an IFL surface-modifying (SAM) agent (such as those discussed earlier in the specification), or a combination thereof. In one embodiment, formamidinium chloride may be added to the lead halide precursor ink. In other embodiments, the halide of any cation discussed earlier in the specification may be used. In some embodiments, combinations of additives may be added to the lead halide precursor ink including, for example, the combination of formamidinium chloride and 5-amino valeric acid hydrochloride. 
     By way of explanation, and without limiting the disclosure to any particular theory of mechanism, it has been found that formamidinium and 5-amino valeric acid improve perovskite PV device stability when they are used as additives or counter-cations in a one-step perovskite device fabrication. It has also been found that chloride, in the form of PbCl 2 , improves perovskite PV device performance when added to a PbI 2  precursor solution in a two-step method. It has been found that the two-step perovskite thin film deposition process may be improved by adding formamidinium chloride and/or 5-amino valeric acid hydrochloride directly to a lead halide precursor solution (e.g., PbI 2 ) to leverage both advantages with a single material. Other perovskite film deposition processes may likewise be improved by the addition of formamidinium chloride, 5-amino valeric acid hydrochloride, or PbCl 2  to a lead halide precursor solution. 
     The additives, including formamidinium chloride and/or 5-amino valeric acid hydrochloride, may be added to the lead halide precursor ink at various concentrations depending on the desired characteristics of the resulting perovskite material. In one embodiment, the additives may be added in a concentration of about 1 nM to about nM. In another embodiment, the additives may be added in a concentration of about n μM to about 1 M. In another embodiment, the additives may be added in a concentration of about 1 μM to about 1 mM. 
     Optionally, in certain embodiments, water may be added to the lead halide precursor ink. By way of explanation, and without limiting the disclosure to any particular theory or mechanism, the presence of water affects perovskite thin-film crystalline growth. Under normal circumstances, water may be absorbed as vapor from the air. However, it is possible to control the perovskite PV crystallinity through the direct addition of water to the lead halide precursor ink in specific concentrations. Suitable water includes distilled, deionized water, or any other source of water that is substantially free of contaminants (including minerals). It has been found, based on light I-V sweeps, that the perovskite PV light-to-power conversion efficiency may nearly triple with the addition of water compared to a completely dry device. 
     The water may be added to the lead halide precursor ink at various concentrations depending on the desired characteristics of the resulting perovskite material. In one embodiment, the water may be added in a concentration of about 1 nL/mL to about 1 mL/mL. In another embodiment, the water may be added in a concentration of about 1 μL/mL to about 0.1 mL/mL. In another embodiment, the water may be added in a concentration of about 1 μL/mL to about 20 μL/mL. 
       FIG. 12  shows images from a cross-sectional scanning electron microscope comparing a perovskite PV fabricated with water ( 5110 ) and without water ( 5120 ). As may be seen from  FIG. 12 , there is considerable structural change in the perovskite material layer ( 5111  and  5121 ) when water is excluded (bottom) during fabrication, as compared to when water is included (top). The perovskite material layer  5111  (fabricated with water) is considerably more contiguous and dense than perovskite material layer  5121  (fabricated without water). 
     The lead halide precursor ink may then be deposited on the desired substrate. Suitable substrate layers may include any of the substrate layers identified earlier in this disclosure. As noted above, the lead halide precursor ink may be deposited through a variety of means, including but not limited to, drop casting, spin casting, slot-die printing, screen printing, or ink-jet printing. In certain embodiments, the lead halide precursor ink may be spin-coated onto the substrate at a speed of about 500 rpm to about 10,000 rpm for a time period of about 5 seconds to about 600 seconds. In one embodiment, the lead halide precursor ink may be spin-coated onto the substrate at about 3000 rpm for about 30 seconds. The lead halide precursor ink may be deposited on the substrate at an ambient atmosphere in a humidity range of about 0% relative humidity to about 50% relative humidity. The lead halide precursor ink may then be allowed to dry in a substantially water-free atmosphere, i.e., less than 20% relative humidity, to form a thin film. 
     The thin film may then be thermally annealed for a time period up to about 24 hours at a temperature of about 20° C. to about 300° C. In one embodiment, the thin film may be thermally annealed for about ten minutes at a temperature of about 50° C. The perovskite material active layer may then be completed by a conversion process in which the precursor film is submerged or rinsed with a solution comprising a solvent or mixture of solvents (e.g., DMF, isopropanol, methanol, ethanol, butanol, chloroform chlorobenzene, dimethylsulfoxide, water) and salt (e.g., methylammonium iodide, formamidinium iodide, guanidinium iodide, 1,2,2-triaminovinylammonium iodide, 5-aminovaleric acid hydroiodide) in a concentration between 0.001M and 10M. In certain embodiments, the thin films may also be thermally post-annealed in the same fashion as in the first line of this paragraph. 
     Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values, and set forth every range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.