Solar cell and method for manufacturing the same

Disclosed is a solar cell including a first electrode, a second electrode, and a first conversion layer disposed therebetween. The first electrode is closer to a light incident side than the second electrode. The first conversion layer is a composition-gradient perovskite. A part of the first conversion layer adjacent to the first electrode has an energy gap less than that of a part of the first conversion layer adjacent to the second electrode.

TECHNICAL FIELD

The technical field relates to a perovskite conversion layer of a solar cell, and in particular it relates to a composition-gradient perovskite layer and method for manufacturing the same.

BACKGROUND

Organic metal perovskite materials are potential materials for solar cells due to their excellent physical properties. Organic lead halide perovskite has a higher efficiency over other perovskite materials. The major conventional method for forming a perovskite layer is coating. For example, two precursors of the perovskite are dissolved in an organic solvent (e.g. DMF), and then spin-coated on an electrode. Alternatively, lead halide (PbX2) can be dissolved in an organic solvent and spin-coated to form a PbX2film on an electrode, and the PbX2film is then dipped in methylammonium iodide (MAI) to form a perovskite film of Pb(CH3NH3)X2I. However, the solvent in the next coating step may dissolve the previously formed perovskite film formed previously. Even if the compositions in each of the coating processes are different, the solvent in different coating processes may dissolve the different compositions in previous coating processes. In short, the general coating processes cannot form a composition-gradient perovskite layer.

Accordingly, a novel method for manufacturing a composition-gradient perovskite layer is called-for.

SUMMARY

One embodiment of the disclosure provides a solar cell, comprising: a first electrode; a second electrode; and a first conversion layer disposed between the first electrode and the second electrode, and the first electrode being closer to a light incident side than the second electrode, wherein the first conversion layer is a composition-gradient perovskite, a part of the first conversion layer adjacent to the first electrode has an energy gap lower than that of a part of the first conversion layer adjacent to the second electrode, and the first conversion layer has a composition of M1mM2(1−m)A[X1xX2(1−x)]3, wherein each of M1and M2is independently a divalent cation of Ge, Sn, or Pb, wherein A is a monovalent cation of methylammonium, ethylammonium, or formamidinium, wherein each of X1and X2is independently a monovalent anion of halogen, wherein M1has a lower atomic number than M2, X1has a higher atomic number than X2, or a combination thereof; wherein 1≧m≧0, 1≧x≧0, and the m and x are greater at a location that is closer to the first electrode.

One embodiment of the disclosure provides a method of manufacturing a solar cell, comprising: providing m parts by mole of M1X12by a first deposition source, providing 1−m parts by mole of M2X22by a second deposition source, and providing a fixed amount of a fixed amount of AX1tX2(1−t)by a third deposition source to deposit a first conversion layer on a first electrode, wherein the first conversion layer is a composition-gradient perovskite; and forming a second electrode on the first conversion layer, wherein a part of the first conversion layer adjacent to the first electrode has an energy gap lower than that of a part of the first conversion layer adjacent to the second electrode, wherein the first conversion layer has a composition of M1mM2(1−m)AX1(2m+t)X2(3−2m−t), m is decreased with a longer deposition time, t is decreased with a longer deposition time, 1≧m≧0, and 1≧t≧0; wherein each of M1and M2is independently a divalent cation of Ge, Sn, or Pb, wherein A is a monovalent cation of methylammonium, ethylammonium, or formamidinium, wherein each of X1and X2is independently a monovalent anion of halogen, wherein M1has a lower atomic number than M2, X1has a higher atomic number than X2, or a combination thereof.

One embodiment of the disclosure provides a method of manufacturing a solar cell, comprising: providing m parts by mole of M1X12by a first deposition source and providing 1−m parts by mole of M2X22by a second deposition source to deposit a M1mM2(1−m)X12mX2(2−2m)layer on a first electrode; providing AX1or AX2by a third deposition source, such that AX1or AX2reacts with the M1mM2(1−m)X12mX2(2−2m); and layer to form a first conversion layer on the first electrode, wherein the first conversion layer is a composition-gradient perovskite of M1mM2(1−m)AX1(2m+1)X2(2−2m)or M1mM2(1−m)AX1(2m)X2(3−2m); and forming a second electrode on the first conversion layer, wherein a part of the first conversion layer adjacent to the first electrode has an energy gap lower than that of a part of the first conversion layer adjacent to the second electrode, wherein m is decreased with a longer deposition time and 1≧m≧0; wherein each of M1and M2is independently a divalent cation of Ge, Sn, or Pb, wherein A is a monovalent cation of methylammonium, ethylammonium, or formamidinium, wherein each of X1and X2is independently a monovalent anion of halogen, wherein M1has a lower atomic number than M2, X1has a higher atomic number than X2, or a combination thereof.

DETAILED DESCRIPTION

One embodiment of the disclosure provides a method for manufacturing a solar cell. As shown inFIG. 1, m parts by mole of M1X12is provided by a deposition source11, 1−m parts by mole of M2X22is provided by a deposition source13, and a fixed amount of a fixed amount of AX1tX2(1−t)is provided by a deposition source15, thereby depositing a conversion layer17on a first electrode19, wherein the conversion layer is a composition-gradient perovskite.FIGS. 2A and 2Bshow concentrations of M1X12, M2X22, and AX1tX2(1−t)at different deposition times in the deposition chamber of embodiments in the disclosure. Note that although only 1 part by mole of M1X12reacts with AX1to form M1AX13at start inFIGS. 2A and 2B, M1X12, M2X22, and AX1tX2(1-t)may react to form M1mM2(1−m)AX12m+tX23−2m−tat the start. In short, deposition can be started at time point T inFIGS. 2A and 2Brather than at time point 0. While the deposition time is increased, the m and t are decreased, 1≧m≧0, and M1mM2(1−m)AX12m+tX23−2m−tcan be represented as M1mM2(1−m)A[X1xX2(1−x)]3, wherein x=(2m+t)/3, and m and x are greater at a location that is closer to the electrode19. Each of M1and M2is independently a divalent cation of Ge, Sn, or Pb. A is a monovalent cation of methylammonium, ethylammonium, or formamidinium. Each of X1and X2is independently a monovalent anion of halogen. M1has a lower atomic number than M2, X1has a higher atomic number than X2, or a combination thereof.

Subsequently, an electrode31can be formed on the conversion layer17, as shown inFIG. 3. In one embodiment, the electrode19is an electrode of a light-incident side, and its composition should be transparent and electrically conductive such as fluorine doped tin oxide (FTO), indium tin oxide (ITO), zinc tin oxide (ZTO), or the like. The electrode31can be a general electrical conductor such as carbon material (e.g. active carbon or graphene) or metal (e.g. gold, silver, copper, aluminum, another electrically conductive metal, or an alloy thereof). In one embodiment, a metal oxide semiconductor material (e.g. titanium oxide, zinc oxide, nickel oxide, or tungsten oxide) can be disposed between the electrode19and the conversion layer17to serve as an electron transport layer. In another embodiment of the disclosure, a hole transport material such as Spiro-OMeTAD, P3HT, CuSCN, CuI, or PEDOT:PSS can be disposed between the electrode31and the conversion layer17to serve as a hole transport layer.

The composition-gradient conversion layer17formed inFIG. 2Ahas an energy gap diagram as shown inFIG. 4A, and the composition-gradient conversion layer17has an energy gap diagram as shown inFIG. 4B. It should be understood that the composition-gradient conversion layer17, with a part adjacent to the electrode19having an energy gap lower than that of a part adjacent to the electrode31, can be formed by the above processes. In addition, the energy gap of the conversion layer17may have other designs as shown inFIG. 4C, 4D, or4E.

In one embodiment, the M1X12provided by the deposition source11inFIG. 1is SnI2, the M2X22provided by the deposition source13inFIG. 1is PbI2, and the AX1tX2(1−t)provided by the deposition source15was (CH3NH3)I. As such, a part of the conversion layer17adjacent to the electrode19can be Sn(CH3NH3)I3with an energy gap of 1.1 eV, a part of the conversion layer17adjacent to the electrode31can be Pb(CH3NH3)I3with an energy gap of 1.5 eV, and the composition between the electrodes19and31can be SnmPb(1−m)(CH3NH3)I3.

In one embodiment, the M1X12provided by the deposition source11inFIG. 1is PbI2, the M2X22A provided by the deposition source13inFIG. 1is PbBr2, and the AX1tX2(1−t)provided by the deposition source15was (CH3NH3)ItBr(1−t). As such, a part of the conversion layer17adjacent to the electrode19can be Pb(CH3NH3)I3with an energy gap of 1.5 eV, a part of the conversion layer17adjacent to the electrode31can be Pb(CH3NH3)Br3with an energy gap of 2.3 eV, and the composition between the electrodes19and31can be Pb(CH3NH3)[IxBr(1−x)]3.

The deposition sources11,13, and15can be sputtering sources or evaporation sources. If the sputtering sources are selected, the ratio of M1X12and M2X22can be fine-tuned by controlling the energy bombarding the target. If the evaporation sources are selected, the ratio of M1X12and M2X22can be fine-tuned by controlling the temperature of the evaporation sources. In addition, the ratio of X1and X2in AX1tX2(1−t)can be fine-tuned by controlling the flow rate of the halogen gas reacting with A.

In another embodiment of the disclosure, a conversion layer18can be deposited on the electrode19before depositing the conversion layer17on the electrode19. As shown inFIG. 5, the conversion layer18is disposed between the electrode19and the conversion layer17. A part of the conversion layer18adjacent to the electrode19has an energy gap higher than that of a part of the conversion layer18adjacent to the conversion layer17, a part of the conversion layer18adjacent to the conversion layer17has an energy gap equal to that of a part of the conversion layer17adjacent to the conversion layer18, and a part of the conversion layer18adjacent to the electrode19has an energy gap lower than that of a part of the conversion layer17adjacent to the electrode31.

In one embodiment, the step of depositing the conversion layer18is described as below. m′ parts by mole of M3X32is provided by a deposition source61, 1−m′ parts by mole of M4X42is provided by a deposition source63, and a fixed amount of AX3t′X4(1−t′)is provided by a deposition source65to deposit the conversion layer18on the electrode19, as shown inFIG. 6. The conversion layer18has a composition of M3m′M4(1−m′)AX3(2m′+t′)X4(3−2m′−t′), m is decreased with a longer deposition time, t is decreased with a longer deposition time, 1≧m′≧0, and 1≧t′≧0. M3m·M4(1−m′)AX3(2m′+t′)X4(3−2m−t′)can be represented as M3m′M4(1−m′)A[X3x′X(1−x′)4]3, wherein x′=(2m′+t′)/3, and m′ and x′ are greater at a location that is closer to the electrode19. Each of M3and M4is independently a divalent cation of Ge, Sn, or Pb, A is a monovalent cation of methylammonium, ethylammonium, or formamidinium, and each of X3and X4is independently a monovalent anion of halogen. M3has a higher atomic number than M4, X3has a lower atomic number than X4, or a combination thereof.

The deposition sources61,63, and65can be sputtering sources or evaporation sources. If the sputtering sources are selected, the ratio of M3X32and M4X42can be fine-fine-tuned by controlling the energy bombarding the target. If the evaporation sources are selected, the ratio of M3X32and M4X42can be fine-tuned by controlling the temperature of the evaporation sources. In addition, the ratio of X3and X4in AX3tX4(1−t)can be fine-tuned by controlling the flow rate of the halogen gas reacting with A.

In one embodiment of the disclosure, the composition of a part of the conversion layer18adjacent the electrode19is gradually changed from Pb(CH3NH3)[IxBr(1−x)]3(0<x<1) to Pb(CH3NH3)I3, and the composition of the conversion layer17is gradually changed from Pb(CH3NH3)I3(the interface between the conversion layers17and18) to Pb(CH3NH3)Br3. In another embodiment, the composition of a part of the conversion layer18adjacent the electrode19is gradually changed from SnmPb(1−m)(CH3NH3)I3(0<m<1) to Sn(CH3NH3)I3, and the composition of the conversion layer17is gradually changed from Sn(CH3NH3)I3(the interface between the conversion layers17and18) to Pb(CH3NH3)I3.

For example, the conversion layers18and17may have energy gap diagrams as shown inFIG. 7A or 7B. Note that the energy gap diagram of the conversion layers18and17can be fine-tuned with other changes inFIGS. 4B to 4E.

In another embodiment, m parts by mole of M1X12is provided by a deposition source11and 1−m parts by mole of M2X22is provided by a deposition source13to deposit a M1mM2(1−m)X12mX2(2−2m)layer on an electrode19. Thereafter, AX1or AX2is provided by a deposition source15, such that AX1or AX2reacts with the M1mM2(1−m)X12mX2(2−2m)layer to form a conversion layer17on the electrode19, wherein the conversion layer17is a composition-gradient perovskite of M1mM2(1−m)AX1(2m+1)X2(2−2m)or M1mM2(1−m)AX1(2m)X2(3−2m). An electrode31is then formed on the conversion layer17, as shown inFIG. 3. M1mM2(1−m)AX1(2m+1)X2(2−2m)can be represented as M1mM2(1−m)A[X1xX2(1−x)]3, wherein x=(2m+1)/3, and m and x are greater at a location that is closer to the electrode19. M1mM2(1−m)AX1(2m)X2(3−m)can be represented as M1mM2(1−m)A[X1xX2(1−x)]3, wherein x=2m/3, and m and x are greater at a location that is closer to the electrode19.

A part of the conversion layer17adjacent to the electrode19has an energy gap lower than that of a part of the conversion layer17adjacent to the electrode31. In the above deposition, m is decreased with a longer deposition time and 1≧m≧0. Each of M1and M2is independently a divalent cation of Ge, Sn, or Pb. A is a monovalent cation of methylammonium, ethylammonium, or formamidinium. Each of X1and X2is independently a monovalent anion of halogen. In the composition of the conversion layer17, M1has a lower atomic number than M2, X1has a higher atomic number than X2, or a combination thereof.

Compared to above embodiments, this embodiment is different due to the M1mM2(1−m)AX1(2m)X2(2−2m)is pre-formed and AX1or AX2are then provided to react with M1mM2(1−m)AX1(2m)X2(2−2m)to form the conversion layer, rather than the M1X1, M2X2, and AX1(or AX2) are simultaneously provided and reacted to directly from the conversion layer. The composition and the energy gap diagram of the conversion layer17in this embodiment are similar to that in the above embodiments and omitted here.

Similar to the above embodiments, a composition-gradient conversion layer18can be further deposited on the electrode19before depositing the conversion layer17in this embodiment. In other words, the conversion layer18is disposed between the conversion layer17and the electrode19. A part of the conversion layer18adjacent to the electrode19has an energy gap higher than that of a part of the conversion layer18adjacent to the conversion layer17, a part of the conversion layer18adjacent to the conversion layer17has an energy gap equal to that of a part of the conversion layer17adjacent to the conversion layer18, and a part of the conversion layer18adjacent to the electrode19has an energy gap lower than that of a part of the conversion layer17adjacent to the electrode31. For example, the energy gap of the conversion layers18and17can be referred toFIGS. 7A and 7B.

In one embodiment, the step of depositing the conversion layer is described as below. m′ parts by mole of M3X32is provided by the deposition source61and 1−m′ parts by mole of M4X42is provided by the deposition source63to deposit a M3m′M4(1−m′)X32m′X4(2−2m′)layer on the electrode19. AX3or AX4is then provided by the deposition source65, such that AX3or AX4reacts with the M3m′M4(1−m′)X32m′X4(2−2m)layer to form a conversion layer18on the electrode19, wherein the conversion layer18is a composition-gradient perovskite of M3m′M4(1−m′)AX3(2m′+1)X4(2−2m′)or M3m′M4(1−m′)AX3(2m′)X4(3−2m′). M3m′M4(1−m′)AX3(2m′+1)X4(2−2m′)can be represented as M3m′M4(1−m′)A[X3x′X4(1−x′)]3, wherein x′=(2m′+1)/3, and m′ and x′ are greater at a location that is closer to the electrode19. M3m′M4(1−m′)AX3(2m′)X4(3−2m′)can be represented as M3m′M4(1−m′)A[X3x′X4(1−x′)]3, wherein x′=(2m′)/3, and m′ and x′ are greater at a location that is closer to the electrode19. m′ is decreased with a longer deposition time and 1≧m′≧0. Each of M3and M4is independently a divalent cation of Ge, Sn, or Pb, A is a monovalent cation of methylammonium, ethylammonium, or formamidinium, and each of X3and X4is independently a monovalent anion of halogen. In the composition of the conversion layer18, M3has a higher atomic number than M4, X3has a lower atomic number than X4, or a combination thereof.

Compared to conventional skills, the processes of manufacturing the perovskite conversion layers in the disclosure are free of solvent. As such, the different perovskite compositions in different layers will not be dissolved and mixed by solvent. In other words, the method of the disclosure may control the perovskite composition in different thicknesses of the conversion layer, thereby tuning the energy gap of the conversion layer to improve the conversion efficiency of the solar cell.

EXAMPLES

Comparative Example 1

InFIG. 3, the electrode19was a TiO2layer with a thickness of 90 nm, the electrode31was a thin gold film, the conversion layer17was a Pb(CH3NH3)I3layer with a thickness of 400 nm, and a hole transport layer (not shown) between the conversion layer17and the electrode31was a Spiro-OMeTAD layer with a thickness of 400 nm. The properties of the above solar cell were simulated and calculated by Analysis of Microelectronic and Photonic Structures 1D (AMPS-1D) as described below. The solar cell had an open-circuit voltage of 1.272V, a short-circuit current of 21.683 mA/cm2, a filling factor of 0.826, and a conversion efficiency of 22.722%.

Comparative Example 2

InFIG. 3, the electrode19was a TiO2layer with a thickness of 90 nm, the electrode31was a thin gold film, and the conversion layer17was a Pb(CH3NH3)I3layer with a thickness of 400 nm. The properties of the above solar cell were simulated and calculated by AMPS-1D as described below. The solar cell had an open-circuit voltage of 0.838V, a short-circuit current of 17.945 mA/cm2, a filling factor of 0.804, and a conversion efficiency of 12.095%.

InFIG. 3, the electrode19was a TiO2layer with a thickness of 90 nm, the electrode31was a thin gold film, a part of the conversion layer17adjacent to the electrode19was Pb(CH3NH3)I3with a thickness of 300 nm, and a composition-gradient part of the conversion layer17was Pb(CH3NH3)[IxBr(1−x)]3with a thickness of 100 nm extending from Pb(CH3NH3)I3to Pb(CH3NH3)Br3. The conversion layer17had an energy gap diagram as shown inFIG. 8A. The properties of the above solar cell were simulated and calculated by AMPS-1D as described below. The solar cell had an open-circuit voltage of 1.284V, a short-circuit current of 21.136 mA/cm2, a filling factor of 0.840, and a conversion efficiency of 22.807%.

InFIG. 3, the electrode19was a TiO2layer with a thickness of 90 nm, the electrode31was a thin gold film, and the conversion layer17was divided to three regions from the electrode19to the electrode31: (1) a composition-gradient part of Pb(CH3NH3)[IxBr(1−x)]3with a thickness of about 50 nm gradually changed to Pb(CH3NH3)I3, wherein the Pb(CH3NH3)[IxBr(1−x)]3had an energy gap that gradually changed from 1.5 eV (or 1.6 eV, 1.8 eV, 2.0 eV, 2.3 eV) to 1.5 eV; (2) a part of Pb(CH3NH3)I with a thickness of about 300 nm, wherein the Pb(CH3NH3)I had an energy gap of 1.5 eV; and (3) a composition-gradient part of Pb(CH3NH3)[IxBr(1−x)]3with a thickness of about 50 nm gradually changed to Pb(CH3NH3)Br3, wherein the Pb(CH3NH3)[IxBr(1−x)]3had an energy gap that gradually changed from 1.5 eV to 2.3 eV. The conversion layer17had an energy gap diagram as shown inFIG. 8B. The properties of the above solar cells, e.g. an open-circuit voltage, a short-circuit current, a filling factor, and a conversion efficiency, were simulated and calculated by AMPS-1D and tabulated in Table 1.

InFIG. 3, the electrode19was a TiO2layer with a thickness of 90 nm, the electrode31was a thin gold film, and the conversion layer17was divided to three regions from the electrode19to the electrode31: (1) a composition-gradient part of Pb(CH3NH3)[IxBr(1−x)]3with a thickness of about 50 nm (or 100 nm, 200 nm, 300 nm, 350 nm) gradually changed to Pb(CH3NH3)I3, wherein the Pb(CH3NH3)[IxBr(1−x)]3had an energy gap that gradually changed from 1.6 eV to 1.5 eV; (2) a part of Pb(CH3NH3)I with a thickness of about 300 nm (or 250 nm, 150 nm, 50 nm, 0 nm), wherein the Pb(CH3NH3)I had an energy gap of 1.5 eV; and (3) a composition-gradient part of Pb(CH3NH3)[IxBr(1−x)]3with a thickness of about 50 nm gradually changed to Pb(CH3NH3)Br3, wherein the Pb(CH3NH3)[IxBr(1−x)]3had an energy gap that gradually changed from 1.5 eV to 2.3 eV. The conversion layer17had an energy gap diagram as shown inFIG. 8C. The properties of the above solar cells, e.g. an open-circuit voltage, a short-circuit current, a filling factor, and a conversion efficiency, were simulated and calculated by AMPS-1D and tabulated in Table 2.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed methods and materials. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.