P-type Transparent Conducting Materials Research Articles

The SrS doped with Cl and K: a promising ambipolar semiconductor for transparent electronics application

Wide-gap semiconductors are essential for current optoelectronics due to the good conductivity and transparency. Although the significant successes have been achieved for n-type transparent conducting materials (TCMs), the p-type TCMs seriously lag behind the n-type counterparts, which severely hinder the developments of the high-performance transparent electronic devices. In present work, we predict the transparent ambipolar conducting can be obtained in SrS by utilizing the hybrid functional method. The Cl substituting S and K substituting Sr (labeled as ClS and KSr) are typical shallow donor and acceptor defects. Compared to conduction band minimum (valence band maximum), the ionization energies for ClS (KSr) would converge to 0.02 (0.14) eV. Using the equilibrium fabricate method, the free electrons (holes) density can reach 1.24 × 1019 cm−3 (1.23 × 1018 cm−3) at room temperature. The effective masses for electron and hole are 0.32 and 0.87 m 0 (m 0 is the mass of a free electron). In the visible light regions, the high transparency can be kept due to its weak inter-band and intra-band absorptions as well as the negligible plasmonic effect. High density of carriers, smaller effective mass and high transparency show SrS doped with Cl and K is a promising ambipolar transparent semiconductor. This work provides insights to realize the high performance ambipolar TCMs. Once the excellent ambipolar TCMs is explored, the high-performance transparent devices are expected in the future.

Chemical Vapor Deposition of Wide-Bandgap p-Type Semiconductor Cuprous Iodide for Optoelectronic Device Applications

Continuous, pinhole-free thin films of transparent conductive materials (TCMs) with p- and n-type conductivity are critical components of optoelectronic devices including photovoltaics (PV), transparent electronics, and LEDs [1]. TCMs with n-type conductivity are widely available in the form of semiconducting oxides [2]; however, p-type TCMs (hole transport materials, HTMs) with suitable conductivity are comparatively rare [1]. Particularly in the rapidly growing field of thin film perovskite PV, device-quality thin films of HTMs with high stability and conductivity are urgently needed to replace the organic HTMs typically employed in perovskite PV research [3]. As such, techniques to deposit inorganic HTM thin films are desired.With a focus on applying HTMs in optoelectronic devices at the commercial scale, these materials must be deposited by a scalable technique yielding thin, continuous, pinhole-free films. Chemical vapor deposition (CVD) is a highly scalable thin film deposition technique widely used in industry, with a proven ability to yield high-quality thin films on large-area substrates [4]. A variety of n-type TCMs are accessible by CVD techniques, but few CVD methods exist for p-type TCMs; examples include atomic layer deposition of NiOx and VOx [5].The cuprous halides (CuX, X = Cl, Br, I), which are optically transparent p-type semiconductors with bandgaps ~3 eV, are promising inorganic HTM candidates. Cuprous iodide is of particular interest due to its low resistivity (~10-2 Ohm·cm), high hole concentration and mobility (~1019 cm-3 and ~1-10 cm2V-1s-1, respectively), and its valence band maximum position (ionization potential: 5.0-5.4 eV), which is well-aligned with common perovskite absorber materials [6]. While CuI crystallite arrays have been obtained by metal-organic CVD [7], CVD of continuous CuI thin films has only been achieved by a two-step vapor conversion process, requiring initial deposition of a copper chalcogen followed by vapor-phase conversion to the halide [6].Our group has recently published a CVD technique enabling direct deposition of continuous CuBr thin films via CVD reaction between hydrogen bromide and vinyltrimethylsilane(hexafluoroacetylacetonato)copper(I) [Cu(hfac)(vtms)] [8], and this technique has been extended to deposition of CuI. X-ray photoelectron spectroscopy indicates pure CuI films with an atomic ratio of approximately 1:1 Cu:I, and x-ray diffraction confirms deposition of γ-CuI. Similar to our observations for CuBr films, substrate identity has significant effects on CuI film continuity. Progress towards CVD of continuous CuI films on substrates of interest for practical application in optoelectronic devices will be discussed, with a particular focus on perovskite PV.[1] A. N. Fioretti and M. Morales-Masis, "Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials," J. Photon. Energy, 10, 042002 (2020).[2] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, "Transparent Electrodes for Efficient Optoelectronics," Adv. Electron. Mater., 3, 1600529 (2017).[3] B. Gil, A. J. Yun, Y. Lee, J. Kim, B. Lee, and B. Park, "Recent Progress in Inorganic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells," Electron. Mater. Lett., 15, 505 (2019).[4] R. Gordon, "Chemical Vapor Deposition of Coatings on Glass," J. Non-Cryst. Solids, 218, 81 (1997).[5] J. A. Raiford, S. T. Oyakhire, and S. F. Bent, "Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells," Energy Environ. Sci., 13, 1997 (2020).[6] R. Heasley, L. M. Davis, D. Chua, C. M. Chang, and R. G. Gordon, "Vapor Deposition of Transparent, p-Type Cuprous Iodide Via a Two-Step Conversion Process," ACS Appl. Energy Mater., 1, 6953 (2018).[7] V. Gottschalch, S. Blaurock, G. Benndorf, J. Lenzner, M. Grundmann, and H. Krautscheid, "Copper iodide synthesized by iodization of Cu-films and deposited using MOCVD," J. Cryst. Growth, 471, 21 (2017).[8] C. M. Chang, L. M. Davis, E. K. Spear, and R. G. Gordon, "Chemical Vapor Deposition of Transparent, p-Type Cuprous Bromide Thin Films," Chem. Mater., 33, 1426 (2021).

Phase stability, phonon, electronic, and optical properties of not-yet-synthesized CsScS2, CsYS2, and APmS2 (A= Li, Na, K, Rb, Cs) materials: Insights from first-principles calculations

Transparent conducting materials (TCMs) combine two exclusive properties, electrical conductivity and visible-light transparency; which make them a unique class of materials. They are required in a wide range of applications in modern life ranging from touchscreen-based devices, flat panel displays, light-emitting diodes (LED), and solar cells. Most of the commercially and widely used TCMs are n-type, whereas the development of high-performance p-type TCMs remains an outstanding challenge in the actual time. Herein, using the newly developed SCAN meta-GGA and the hybrid HSE06 functionals, we have explored the structural stability and physical properties of not-yet-synthesized ternary materials CsScS2, CsYS2, and APmS2 (A = Li, Na, K, Rb, Cs) to identify promising p-type TCMs. As result, the calculated formation energy, phase diagram and phonon dispersion curves confirm that these materials are thermodynamically stable and feasible to synthesize experimentally. All these materials, have large optical band gaps (larger than 3.4 eV), small hole effective masses (except for LiPmS2), and have no absorption and weak reflectivity of the visible light. Our work demonstrates that these compounds have suitable properties for p-type TCMs applications.

Modulation effect of low-electronegativity non-metallic elements on the electronic structure of group-IVB transition metal oxides

Transparent conducting materials (TCMs) are widely used in many optoelectronic devices. Transition metal oxides account for a large proportion of transparent conducting materials (TCMs). However, some transition metal oxides with p-type TCMs characteristics usually hold large holes effective mass, the performance is not as good as n-type TCMs. The reason is that the VBM (maximum valence band) of most transition metal oxides is mainly composed of strongly localized O-2p orbitals. Reducing the localization degree of electrons in the VBM is the key to solving the problem. In order to study the modulation effect for the addition of nonmetal constituents with less electronegativity (such as S/Se/Te) on the VBM for transition metal oxides, we perform a systematic theoretical study of 12 kinds of MmXnYl (M = Ti, Zr, Hf and X, Y= O, S, Se, Te) based on density functional theory (DFT), including the structural, electronic, and optical properties. For the potential TCMs candidates (c-ZrOS, t-ZrOS, c-HfOS) that exhibit excellent conductivity and high transparency, the dynamic stability is studied through phonon spectra. For the transition metal compound with the same symmetry, a convenient method to compare the effective mass of holes and band gap is proposed, that is, a larger electronegativity of the entire compound usually means a larger band gap and effective mass of holes. The effective mass of electrons is primarily determined by the localization of the d-orbital of transition metal, the smaller the electronegativity of transition metals means the smaller effective mass of electrons and larger band gap.

Screening criteria for high-performance p-type transparent conducting materials and their applications

To accelerate discovery of promising p-type transparent conducting materials (TCMs), a screening strategy is formulated based on calculable selection metrics of thermodynamic stability, wide gap, low hole effective mass, and p-type dopability. Using this screening strategy, we identified three best-of class p-type TCM candidates (CaTe, BaTe and BeS) with combination properties of good transparency, high carrier mobility, and excellent hole dopability. Based on ionization energy calculations, we have established a concise and reliable criterion for assessing p-type performance. It is concluded that BeS is readily accessible an intrinsic p-type TCM, while CaTe and BaTe requiring extrinsic doping. Defect calculations are performed for the three compounds, providing strong support for our results. Although the defect calculations indicate a lack of shallow hole-producing defects in CaTe and BaTe, they both would be promising p-type TCMs when introducing impurities such as Na and K acceptor dopants. BeS contains an acceptor-type defect with a low formation energy (Be vacancies), which is responsible for its intrinsic p-type behavior. This physically formulated screening strategy would motivate the exploration and design of other advanced functional materials, and our established criterion could be another route to identify the p/n-type behavior of materials.

Perspective on the band structure engineering and doping control of transparent conducting materials

Transparent conducting materials (TCMs), which combine high electrical conductivity and high optical transmission in the visible spectral range, are needed in many modern optoelectronic devices such as solar cells, flat-panel displays, touch-screen sensors, light emitting diodes, and transparent thin film transistors. However, many physical properties of the TCMs are still not very well understood. Understanding the band structure and physical origin of the unique properties of the TCMs is, therefore, crucial for the future design of these fascinating materials. In this Perspective, we will first present a brief review of the unique band structure and doping control of TCMs. In particular, we will discuss (i) the fundamental band structures and defect properties for the TCMs and why most of them are oxides (transparent conducting oxides, TCOs); (ii) how to achieve simultaneously high transparency and conductivity in n-type TCMs; (iii) why p-type TCOs are difficult to achieve; (iv) how to modify the band structure or design new materials to achieve p-type TCMs or even bipolarly dopable TCMs. Finally, we will discuss some of the remaining challenges and opportunities for the development of TCMs in the near future.

A P-type mid-infrared transparent semiconductor LaSe2 film with small hole effective mass and high carrier concentration

P-type transparent conductive materials (TCMs) are urgently needed in the development of photoelectric devices. In particular, the P-type TCMs that can be applied in the mid-infrared range are even rarer due to the conflict between the transparent range and the conductivity of materials. In this work, a P-type mid-infrared transparent conductive LaSe2 film is obtained by a two-step method combining the RF sputtering and a selenized annealing process. The crystal structure of the film has been confirmed by x-ray diffraction and Raman spectrum analysis. According to the Hall effect measurement results, the LaSe2 film has a higher conductivity (about 3.6 S/cm) than that of traditional P-type mid-infrared TCMs, which is attributed to its ten times higher carrier concentration (about 1019 cm−3) and a much smaller hole effective mass (about 0.34 me) compared to the conventional P-type mid-infrared TCMs. The transmittance (about 75%) is at the same level as that of the traditional P-type mid-infrared TCMs. In a sense, the LaSe2 is a promising candidate material for the development of mid-infrared photoelectric devices.

Chalcogenide Perovskite YScS3 as a Potential p-Type Transparent Conducting Material

Transparent conducting materials (TCMs) have been widely used in optoelectronic applications such as touchscreens, flat panel displays and thin film solar cells. These applications of TCMs are currently dominated by n-type doped oxides. High-performance p-type TCMs are still lacking due to their low hole mobility or p-type doping bottleneck, which impedes efficient device design and novel applications such as transparent electronics. Here, based on first-principles calculations, we propose chalcogenide perovskite YScS3 as a promising p-type TCM. According to our calculations, its optical absorption onset is above 3 eV, which allows transparency to visible light. Its hole conductivity effective mass is 0.48m0, which is among the smallest in p-type TCMs, suggesting enhanced hole mobility. It could be doped to p-type by group-II elements on cation sites, all of which yield shallow acceptors. Combining these properties, YScS3 holds great promise to enhancing the performance of p-type TCMs toward their n-type counterparts.

Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials

Transparent conductive materials (TCMs) with high p-type conductivity and broadband transparency have remained elusive for years. Despite decades of research, no p-type material has yet been found to match the performance of n-type TCMs. If developed, the high-performance p-type TCMs would lead to significant advances in a wide range of technologies, including thin-film transistors, transparent electronics, flat screen displays, and photovoltaics. Recent insights from high-throughput computational screening have defined design principles for identifying candidate materials with low hole effective mass, also known as disperse valence band materials. Particularly, materials with mixed-anion chemistry and nonoxide materials have received attention as being promising next-generation p-type TCMs. However, experimental demonstrations of these compounds are scarce compared to the computational output. One reason for this gap is the experimental difficulty of safely and controllably sourcing elements, such as sulfur, phosphorous, and iodine for depositing these materials in thin-film form. Another important obstacle to experimental realization is air stability or stability with respect to formation of the competing oxide phases. We summarize experimental demonstrations of disperse valence band materials, including synthesis strategies and common experimental challenges. We end by outlining recommendations for synthesizing p-type TCMs still absent from the literature and highlight remaining experimental barriers to be overcome.

Transparent p-Type Semiconductors: Copper-Based Oxides and Oxychalcogenides

While p-type transparent conducting materials (TCMs) are crucial for many optoelectronic applications, their performance is still not satisfactory. This has impeded the development of many devices such as photovoltaics, sensors, and transparent electronics. Among the various p-type TCMs proposed so far, Cu-based oxides and oxychalcogenides have demonstrated promising results in terms of their optical and electrical properties. Hence, they are the focus of this current review. Their basic material properties, including their crystal structures, conduction mechanisms, and electronic structures will be covered, as well as their device applications. Also, the development of performance enhancement strategies including doping/co-doping, annealing, and other innovative ways to improve conductivity will be discussed in detail.

Database Screening of Ternary Chalcogenides for P-type Transparent Conductors

In this work, we investigated ternary chalcogenide semiconductors to identify promising p-type transparent conducting materials (TCMs). High-throughput calculations were employed to find the compounds that satisfies our screening criteria. Our screening strategy was based on the size of band gaps, the values of hole effective masses, and p-type dopability. Our search led to the identification of seven promising compounds (IrSbS, Ba2GeSe4, Ba2SiSe4, Ba(BSe3)2, VCu3S4, NbCu3Se4, and CuBS2) as potential TCM candidates. In addition, branch point energy and optical absorption spectra calculations support our findings. Our results open a new direction for the design and development of p-type TCMs.

New energy with ZnS: novel applications for a standard transparent compound

We revise the electronic and optical properties of ZnS on the basis of first principles simulations, in view of novel routes for optoelectronic and photonic devices, such as transparent conductors and plasmonic applications. In particular, we consider doping effects, as induced by Al and Cu. It is shown that doping ZnS with Al imparts a n-character and allows for a plasmonic activity in the mid-IR that can be exploited for IR metamaterials, while Cu doping induces a spin dependent p-type character to the ZnS host, opening the way to the engineering of transparent p-n junctions, p-type transparent conductive materials and spintronic applications. The possibility of promoting the wurtzite lattice, presenting a different symmetry with respect to the most stable and common zincblende structure, is explored. Homo- and heterojunctions to twin ZnO are discussed as a possible route to transparent metamaterial devices for communications and energy.

High-Throughput Design of Non-oxide p-Type Transparent Conducting Materials: Data Mining, Search Strategy, and Identification of Boron Phosphide

High-performance p-type transparent conducting materials (TCMs) are needed in a wide range of applications ranging from solar cells to transparent electronics. p-type TCMs require a large band gap (for transparency), low hole effective mass (for high mobility), and hole dopability. It has been demonstrated that oxides have inherent limitations in terms of hole effective masses making them difficult to use as a high-performance p-type TCM. In this work, we use a high-throughput computational approach to identify novel, non-oxide, p-type TCMs. By data mining a large computational data set (more than 30,000 compounds), we demonstrate that non-oxide materials can lead to much lower hole effective masses but to the detriment of smaller gaps and lower transparencies. We propose a strategy to overcome this fundamental correlation between low effective mass and small band gap by exploiting the weak absorption for indirect optical transitions. We apply this strategy to phosphides and identify zinc blende boron pho...

First-principles prediction of a promising p-type transparent conductive material CsGeCl3

Most reported p-type transparent conductive materials are Cu-based compounds such as CuAlO2 and CuCrO2. Here, we report that compounds based on ns2 cations with low binding energy can also possess high valence band maximum, which is crucial for the p-type doping according to the doping limit rules. In particular, CsGeCl3, a compound with valence band maximum from ns2 cations, is predicted as a promising p-type transparent conductive material by first-principles calculations. Our results show that the p-type defect Ge vacancy dominates its intrinsic defects with a shallow transition level, and the calculated hole effective masses are low in CsGeCl3.

Li-doped NiMgO thin films as a promising p-type transparent conductive material with wide band-gap

Transparent conductive p-type Li-doped NiMgO thin films were prepared on quartz substrates by pulsed laser deposition. The effects of oxygen pressure on the properties of the films were investigated. The results demonstrated that the Mg-alloying enhances the transparency of the films and Li-doping improves the conductivity. A minimum resistivity of 19.26Ωcm, with an average optical transmittance higher than 85% in the visible region and a wide band-gap of 3.87eV, was obtained for the film prepared at the oxygen pressure of 5Pa. The p-type conduction of Li-doped NiMgO film was further confirmed by a rectifying Li-doped NiMgO/i-ZnO/Al-doped ZnMgO heterojunction.

First-principles study of γ-CuI for p-type transparent conducting materials

γ-CuI has attracted considerable attention recently as a p-type transparent conductive material. In this paper, we have investigated the hole effective mass, intrinsic defects and group VI-A impurities in γ-CuI by first-principles calculations. We found that the hole effective mass of γ-CuI is light, in line with the high p-type mobility observed in experiments. The p-type conductance is expected to originate from Cu vacancies, which have a low formation energy with no significant n-type compensating defects. The relative high transition level of Cu vacancy, however, may lead to a low hole concentration in the γ-CuI sample. Additionally, no shallow transition levels were found in γ-CuI with substitutional group VI-A impurities at I sites.

First-principles study of Be doped CuAlS2 for p-type transparent conductive materials

CuAlS2 has attracted much attention recently as a p-type transparent conductive material. In this paper, we investigate the site preference of substitutional Be in CuAlS2 and the transition level of BeAl using the first-principles calculation. We find that Be would be doped effectively at Al sites in CuAlS2 as a good p-type dopant. In addition, we speculate that Be–Mg or Be–Zn codoped CuAlS2 could have a mobility enhancement and thus a good p-type conductivity due to low lattice distortion.

P-type transparent conductive BaSnO3: A first-principles calculations

Based on density functional theory calculations, the electronic properties of N-doped BaSnO3 and N and Sb codoping are investigated. It is found that codoping with N acceptors and Nb donors in a ratio of 2 ∶1 is suitable for the fabrication of low-resistivity p-type BaSnO3. Our results indicate that codoping with N acceptors and Nb donors is a prospective candidate as a p-type transparent conductive material.

First-principles study of CuAlS2 for p-type transparent conductive materials

We have investigated the intrinsic defects, and Mg, Zn impurities in CuAlS2, as well as their induced carrier concentrations using the first-principles calculations. We find that p-type conductivity could be dominated by the intrinsic defects VCu, CuAl or the doping defects ZnAl, MgAl in different samples. Although vacancy Cu is an important acceptor in CuAlS2, a Cu-deficient sample is not the best for p-type conductivity due to the compensation from AlCu defects. In fact, our results indicate that Zn is the best choice for p-type doping for CuAlS2, in particular under Cu-rich and Al-poor condition, which is in line with the experimental results. The main difference in carrier concentration between theory and experiment is expected to have originated from the multiphase of the samples prepared in experiments, instead of a single crystal. We also find that there is no remarkable difference in the effective mass in samples dominated by different defects, such as CuAl, MgAl, ZnAl and Cu vacancy. The significant difference in the experimentally observed hole mobility may be dominated by their mean free time τp.

A promising p-type transparent conducting material: Layered oxysulfide [Cu2S2][Sr3Sc2O5

Sr 3 Cu 2 Sc 2 O 5 S 2 , a layered oxysulfide, composed of anti-PbO-like [Cu2S2] slabs alternating with perovskitelike [Sr3Sc2O5] slabs, was systematically studied as a p-type transparent conducting material. The material has a wide energy gap of 3.1eV and a p-type electrical conductivity of 2.8Scm−1 at room temperature. The hole mobility of +150cm2V−1S−1 at room temperature, which is much higher than the typical value of ∼10−1–10cm2V−1S−1 found in other copper compounds. The performances of bulk undoped Sr3Cu2Sc2O5S2 show the promise of copper oxysulfides as a class of p-type transparent conductive materials that is essential for optoelectronic applications.