Query: New n-Type Transparent Conducting Oxides Tadatsugu Minami

Candidate papers:

abstract: Most research to develop highly transparent and conductive thin films has focused on n type semiconductors consisting of metal oxides. Historically, transparent conducting oxide (TCO) thin films composed of binary compounds such as SnO 2 and In 2 O 3 were developed by means of chemical and physical deposition methods. Impurity doped SnO 2 (Sb or F doped SnO 2 e.g. SnO 2 :Sb or SnO 2 F) and In 2 O 3 Sn (indium tin oxide, ITO) films are in practical use. In addition to binary compounds, ternary compounds such as Cd 2 SnO 4 CdSnO 3 and CdIn 2 O 4 were developed prior to 1980, but their TCO films have not yet been used widely.
author_names: Tadatsugu Minami
title: New n Type Transparent Conducting Oxides
year: 2000

abstract: In contrast to n type transparent conducting oxides (TCOs) very few p type TCOs have been discovered to date. In this work, we predicted two new tin germanate based compounds (Sn2GeO4) as potential p type TCOs with exceptionally low hole effective masses and wide band gap energies. Through detailed electronic structure calculations, we revealed that the Sn2GeO4 compounds possess sufficiently wide band gaps (3.24 eV) for transparency, and very small effective masses (0.46) for hole carriers due to the influence of divalent Ge2+ Our study shows the potential for band engineering of Sn2+ and Ge2+ cations with (n 1)d10ns2 electronic configurations as p type TCOs; this could expand the materials family for the future design and development of p type TCOs.
author_names: Jun-Ling Yu

Junjie Wang

Mukesh Kumar

Naoto Umezawa

Hideki Abe
title: Design of p type transparent conducting oxides Sn2GeO4 by an ab initio evolutionary structure search
year: 2018

abstract: P type transparent conducting oxide films consisting of a new multicomponent oxide composed of In2O3 and Ag2O have been prepared by rf magnetron sputtering. After postannealing at a temperature of 500 degC in air, In2O3 Ag2O thin films prepared using In2O3 Ag2O targets with Ag2O contents of 40 60 wt exhibited p type conduction. A resistivity of 10 1 10 3 O cm and an average transmittance above 20% in the visible range were obtained in the p type amorphous In2O3 Ag2O films. A resistivity of 8.8x10 3 O cm, Hall mobility of 17 cm2/Vs and hole concentration of 4.2x1019 cm 3 were obtained in a film prepared with an Ag2O content of 50 wt
author_names: Tadatsugu Minami

Koji Shimokawa

Toshihiro Miyata
title: P type transparent conducting In2O3 Ag2O thin films prepared by rf magnetron sputtering
year: 1998

abstract: Abstract New multicomponent transparent conducting oxide thin films have been prepared by both r.f. and d.c. magnetron sputtering using ZnO V 2 O 5 targets. A minimum resistivity of 5.3x10 4 O cm was obtained in ZnO:V films prepared by d.c. magnetron sputtering at a substrate temperature of 180 degC with a V content of 1 at. ZnO V 2 O 5 thin films prepared using targets with V contents from approximately 50 to 70 at. were insulators identified as a ternary compound, ZnV 2 O 4 The resistivity of ZnO V 2 O 5 films markedly decreased as the V content was increased above approximately 80 at. Vanadium oxide thin films with a thickness of 25 nm exhibited a resistivity of 5x10 4 O cm and an average transmittance above 70% in the visible range. The film was very stable over 1000 h in a hydrochloric acid.
author_names: Toshihiro Miyata

Shingo Suzuki

Makoto Ishii

Tadatsugu Minami
title: New transparent conducting thin films using multicomponent oxides composed of ZnO and V2O5 prepared by magnetron sputtering
year: 2002

abstract: Transparent conducting oxides (TCOs) are essential to many technologies including solar cells and transparent electronics. The search for high performance n or p type TCOs has mainly focused on materials offering transport through band carriers instead of small polarons. In this work, we break this paradigm and demonstrate using well known physical models that, in certain circumstances, TCOs exhibiting transport by small polarons offer a better combination of transparency and conductivity than materials conducting through band transport. We link this surprising finding to the fundamentally different physics of optical absorption for band and polaronic carriers. Our work rationalizes the good performances of recently emerging small polaronic Cr based p type TCOs such as Sr doped LaCrO$_3$ and outlines design principles for the development of high performance TCOs based on transport by small polarons. This opens new avenues for the discovery of high performance TCOs especially p type.
author_names: Guillaume Brunin

Gian-Marco Rignanese

Geoffroy Hautier
title: Are Small Polarons Always Detrimental to Transparent Conducting Oxides
year: 2018

abstract: The development of high performance transparent conducting oxides is critical to many technologies from transparent electronics to solar cells. Whereas n type transparent conducting oxides are present in many devices, their p type counterparts are not largely commercialized, as they exhibit much lower carrier mobilities due to the large hole effective masses of most oxides. Here we conduct a high throughput computational search on thousands of binary and ternary oxides and identify several highly promising compounds displaying exceptionally low hole effective masses (up to an order of magnitude lower than state of the art p type transparent conducting oxides) as well as wide band gaps. In addition to the discovery of specific compounds, the chemical rationalization of our findings opens new directions, beyond current Cu based chemistries, for the design and development of future p type transparent conducting oxides.
author_names: Geoffroy Hautier

Anna Miglio

Gerbrand Ceder

Gian-Marco Rignanese

Xavier Gonze
title: Identification and design principles of low hole effective mass p type transparent conducting oxides
venue: Nature communications
year: 2013

abstract: Transparent conducting oxides (TCOs) are unique materials with high electrical conductivity and optical transparency and have been extensively used in optoelectronic devices. However, the prototype n type TCO, Sn doped In2O3 (ITO) is limited by the rarity and high cost of indium. In contrast, SnO2 is a promising alternative candidate, which is a low cost and nontoxic material and also exhibits electrical and optical properties, compared to those of ITO. Here, we present a first principles based computer screening system to search for suitable dopants for monodoping or codoping SnO2 to develop new SnO2 based TCO materials. The screening is based on an efficient and reliable way of calculating the effective mass, the band gap, the formation energy, and the binding energy. The outcomes of the screening include all already known successful SnO2 based TCO materials (Sb doped SnO2, ATO; F doped SnO2, FTO) and also some new ones (P doped SnO2, PTO; F and P codoped SnO2, FPTO) which would be hopeful materials o.
author_names: Daojian Cheng

Minming Zhang

Jianfeng Chen

Chenxi Yang

Xiao-Fei Zeng

Dapeng Cao
title: Computer Screening of Dopants for the Development of New SnO2 Based Transparent Conducting Oxides
year: 2014

abstract: The development of high performance transparent conducting oxides (TCOs) is critical to many technologies from transparent electronics to solar cells. While n type TCOs are present in many devices, current p type TCOs are not largely commercialized as they exhibit much lower carrier mobilities, due to the large hole effective masses of most oxides. Here, we conduct a high throughput computational search on thousands of binary and ternary oxides and identify several highly promising compounds displaying exceptionally low hole effective masses (up to an order of magnitude lower than state of the art p type TCOs) as well as wide band gaps. In addition to the discovery of specific compounds, the chemical rationalization of our findings opens new directions, beyond current Cu based chemistries, for the design and development of future p type TCOs. 1 ar X iv :1 30 4. 60 54 v1 co nd m at .m tr lsc i] 2 2 A pr 2 01 3 Transparent conducting oxides (TCOs) are compounds exhibiting high electrical conductivity and transparency to visible light. Those materials are needed in many applications from solar cells, where a TCO thin film provides electrical contact without impeding the flux of visible light reaching the device, to transparent transistors that could, for instance, be integrated in windows.[1 5] The main strategy to achieve the two antagonistic properties of high conductivity and transparency is to use wide band gap oxides (favoring transparency) doped with a significant amount of mobile charge carriers, either holes (ptype) or electrons (n type)[6] n TCOs (e.g. indium tin oxide, ITO) are already present in many modern devices but p TCOs have not been largely commercialized as their carrier mobilities stand an order of magnitude behind their n counterparts. This situation impedes many critical technological developments from more efficient organic and thin film solar cell designs, benefiting from a better band matching by using pinstead of n TCOs,[7, 8] to the entire new field of transparent electronics which requires both pand n type TCO materials.[2, 9 13] There is a fundamental reason to the difficulty of developing high mobility p type TCOs: the localized oxygen p nature of the valence band in most oxides makes those bands very flat and leads to large hole effective masses.[12, 13] The field of p type TCOs received most of its impulse a decade ago when Kawazoe et al. demonstrated that CuAlO2 delafossite could show encouraging p type conductivity and optical transparency in the visible.[14] The unusual hole mobility of CuAlO2 was explained by a large hybridization of the oxygen orbitals with 3d10 electrons in the Cu1+ closed shell, lowering the oxygen character and leading to dispersive (low effective mass) valence band. This finding led to the outline of a design rule for p type TCOs requiring the presence of Cu1+ and motivated the study of a very large range of Cu based materials [12, 13] such as other delafossites (e.g. CuCrO2,[15] SrCu2O2, [16, 17] or Cu based oxychalcogenides.[18] To this day, the question remains open wether alternative chemistries and design rules could lead to materials with lower hole effective mass. Answering this question is critical for the p type TCO field as it would enable the identification of the high hole mobility oxides that the TCO community has been looking for. Traditionally, design principles are developped by the rationalization of experimentally observed data. In this work, we take an alternative path using a database of high throughput ab initio computed data containing electronic structure for thousands of binary and ternary oxides.[19 22] By browsing this database, we identify the compounds and chemistries leading to low hole
author_names: Geoffroy Hautier

Anna Miglio

Gerbrand Ceder

Gian-Marco Rignanese

Xavier Gonze
title: Low Hole Effective Mass p type Transparent Conducting Oxides: Identification and Design Principles
year: 2013

abstract: Abstract Motivated by extensive investigations on the In2O3 based multicomponent transparent conducting oxides (TCOs) we want to know the carrier transport properties in these systems and how they evolve with adjusting of geometric structure and constituent elements. Guided by the empirical minimum effective mass physics, we select nine impurities M (M Sn, Zn, Cd, Hg, Mn, Ni, Co, Ga and Ge) to tune the effective mass (m* of In2O3 based TCOs. By means of systematic theoretical investigations, we find that in impurity M isolated or corporately doped In2O3 materials, the substitutional position for dopant M is determined by the charge state. Codoping Sn and other eight impurities into In2O3 (to form IMTO) is an effective strategy to reduce the indium content in In2O3 based TCOs materials. For the recognized n type carrier contributor, namely, VO defect, it induce spatial localization and orbital localization effects in electronic structures and thus enlarge m* which are caused by the large lattice distortion and complicated orbital wavefunction hybridizations. However, for IMTO:VO (M Zn, Ga and Hg) systems, both localization effects are weakened, leading to a decrease of m* It even reduces by half value for In Hg Sn O:VO systems. This systematic work in In2O3 based materials may be helpful in designing of a new range of high performance TCOs.
author_names: Ying-Bo Lu

Haozhi Yang

Xin Yanqing

Wei-Yan Cong
title: Modulation effect on the effective mass of free carriers induced by multicomponent elements in In2O3 based transparent conducting oxides
year: 2017

abstract: Clean and sustainable solar energy is regarded as one of the most reliable and abundant energy sources to replace fossil fuels. To harvest this energy, in the past several decades, the research trend has been towards exploring novel materials and photon to electron mechanisms to achieve higher efficiency in solar energy conversion applications, such as photovoltaic (PV) cells. The PV effect is used to directly harvest solar energy by converting the incident photons into following free charge carriers and thus produce electricity. The emerging PV cells mainly differ in how they operate in practice, that is, in the mechanisms that make the sequence of the generation, separation and transport of electronic charge carriers possible. Elucidating those mechanisms is of fundamental importance for understanding the working principle of each solar cell type, and for its further performance optimization. In conventional p n junction based PV cells, the charge separation is determined by the existence of a gradient in the electrochemical potential, also known as intrinsic built in electric fields. Moreover, solar driven water splitting and hydrogen generation technologies that produce hydrogen (H2 gas) and oxygen (O2 gas) by directly decomposing water using an artificial photocatalytic electrode have been extensively studied as a fundamental technology for the future, due to its simplicity, low cost operation and the use of nearly neutral pH water, such as seawater for large scale solar fuel production. In the semiconductor photocatalysts, the carrier extraction is no longer limited by thermodynamic diffusion, but the transport of spatially separated electron hole pairs to the photocatalyst surface is determined by the surface band bending. Ferroelectric (FE) oxides have recently emerged as a new alternative pathway to achieve the separation of photo generated charge carriers, and their application in photon to current (e.g. PV cells, photodetectors) and photoelectrochemical (PEC) devices was recently started to be explored. Since the discovery of PV effect in these materials over 50 years ago, ferroelectric devices including solar cells (FESC) and PEC cells have attracted significant attention owing to many unique advantages. This technology involves a simplified structure and fabrication methods as well as stable and abundant materials. Different from the p n diode or Schottky diode solar cells, in the FESC, FE polarization plays a dominant role in charge separation and transport. FESC provides reversible directions of photocurrent and photovoltage by polarization direction switching, and also generates above bandgap open circuit voltages (Voc up to 40 V) which potentially permit to surpass the Shockley Queisser limit observed in traditional semiconductors cells. While for a long time such devices were characterized by weak performance values, recent advances led to significant breakthroughs by using multiferroic materials. Multiferroics combine two ferroic functionalities (specifically FE, ferromagnetic or ferroelastic) and typically possess a magnetic order parameter besides the FE one and the electron electron interaction regulating the magnetic ordering induced a smaller gap (e.g. 2.6 2.7 eV for BiFeO3 and 1.4 2.4 eV for Bi2FeCrO6) than other FE materials (e.g. 3.2 3.6 eV for La doped Pb(Zr,Ti)O3 and 3.2 eV for BaTiO3) Among these multiferroics, double perovskite Bi2FeCrO6 (BFCO) is highly promising in PV and photocatalytic applications due to its nontoxicity, chemical stability, narrow bandgap, huge light absorption coefficient (2.5 x 105 cm 1) large remnant polarization (55 mC cm 2 at room temperature (RT) and magnetization (160 emu cm 3) A breakthrough in the field of PV and PEC devices occurred through our recent study on multiferroic BFCO epitaxial thin films, which demonstrated a high efficiency solar energy conversion (solar to electrical or chemical energy) In such material, lower band gap and large FE polarization promote an effective charge carrier generation and separation. Single crystalline BFCO with higher ratio of Fe/Cr cation ordering (R0.5 5.1% showed a lower bandgap (Eg1.4 1.8 eV) accompanied with weak FE polarization (P5 20 mC cm 2) which exhibit thus a semiconductor behavior. In despite of a larger absorption of sun light by semiconducting BFCO films, the weak FE polarization induced internal electric field decreases the separation power of photogenerated carriers and increases the recombination loss. This dramatically affects the performance of the devices. These results clearly suggest a relationship between the optical property, ferroelectricity and crystal structure of BFCO thin films. To advantageously exploit the semiconducting properties of BFCO for PV application, the p i n device architectures have to be designed and developed. Here, an intrinsic semiconductor is sandwiched between a heavily doped p and n layers. Semiconductor material absorbs a certain portion of the solar spectrum and adjacent layers (electrodes) are required to extract the photo generated carriers for conveyance to an external electrical load. The p type layer in p i n devices is possible incident photons enter the intrinsic absorber layer (i of the device for conversion into charge carriers. This requires that all other "photo passive" but functional layers in the PV cell that lie in the path of photons traversing to the absorber should not absorb or back reflect any of the light before it reaches the intrinsic absorber. That is, the window layers must be highly transparent, i.e. having a wider bandgap than the absorber and thus a much lower absorption coefficient in the spectral range of light used for photo conversion. Electrically, the p layer should have hole conduction in order to transport the photogenerated holes and block the electrons. Based on these requirements, the p type layer in p i n devices should be the p type transparent conducting oxides (p TCOs) The work performed in this thesis was therefore driven by two main objectives: (1) synthesis and understanding the fundamental physical properties (i.e. structural, electrical, and optical) of p TCOs thin films; (2) design and investigating the multiferroic BFCO thin film absorber based devices for efficient solar energy conversion applications including photodetectors, PV and PEC devices. The results obtained in this work are resumed in two sections as follows: In the first section, we synthesized the p type transparent conducting thin films and studied their structural, electrical and optical properties. (1) Perovskite p type In doped SrTiO3 (SrInxTi1 xO3 with In concentration in the range 0<=x<=0.15) thin films were grown on LaAlO3 substrates using a pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) combination technique. (2) The In STO (ISTO, 0.1<=x<=0.15) films grown under oxygen pressure of 10 7 10 3 Torr show an optimal range of high transmittance ~70% low resistivity ~10 2 O cm) high carrier concentration of ~3x1019 cm 3 with mobility of ~5 cm2/Vs, and large Eg>=3.2 eV. The second section is focused on solar energy conversion applications of BFCO thin films based devices: (1) the photodiodes based on the epitaxial BFCO/SrRuO3 (SRO) thin films were fabricated by using PLD techniques. The photodiodes with a large ideality factor (n5.0) exhibits a substantial photocurrent at forward biased voltages (photoconductive effect) and a fast transient response (in the order of 10 2 s) The tailoring of photoelectric performance was achieved by switching FE polarization state of BFCO (Eg2.5 eV; P40 mC cm 2) The ultrafast charge transfer at BFCO/SRO heterojunction was investigated by time resolved photoluminescence. A peak sensitivity was measured as 0.38 mA/W at 500 nm by photoresponsivity spectroscopy. (2) We reported the fabrication of multiferroic BFCO thin films (Eg1.7 2.4 eV; P14 44 mC cm 2) based PV devices with p i n heterojunction by PLD. A p type NiO thin film acting as hole transporting/electron blocking layer and a typical n type Nb STO acting as electron transporting layer were used to form the double interfaced heterojunctions. Under 1 sun illumination, the optimized p i n devices yielded an open circuit voltage of ~0.53 V and a short circuit current density of ~8.0 mA cm 2, leading to a PCE of ~2.0% a four fold enhancement compared to that of the i n device architecture. (3) The n type BFCO thin films coated with a p type transparent conducting NiO layer were implemented as a heterojunction photoelectrode by PLD for solar driven water splitting. The tailoring of PEC performance of the bare BFCO (Eg1.8 eV; P20 mC cm 2) based photoanodes was achieved by effectively tuning the FE polarization state, and thus resulted in a 1.5 fold increase in photocurrent density. A 4 fold enhancement of photocurrent density, up to 0.4 mA cm 2 (at +1.23 V vs. RHE) in 1 M Na2SO4 (pH 6.8) electrolyte under 1 sun illumination was carried out by coating the bare BFCO photoanodes with a p type transparent conducting NiO layer acting as an electron blocking and protection layer. The stable operation of p NiO/n BFCO heterojunction photoanodes was confirmed by observing a constant current density over 4 hours.
author_names: Wei Huang
title: Transparent conducting oxides and multiferroic perovskites for solar energy conversion applications.
year: 2018