Database Screening of Ternary Chalcogenides for P-type Transparent

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Database Screening of Ternary Chalcogenides for p-type Transparent Conductors Ramya Kormath Madam Raghupathy, Hendrik Wiebeler, Thomas D. Kuehne, Claudia Felser, and Hossein Mirhosseini Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b02719 • Publication Date (Web): 12 Sep 2018 Downloaded from http://pubs.acs.org on September 13, 2018

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Chemistry of Materials

Database Screening of Ternary Chalcogenides for P-Type Transparent Conductors Ramya Kormath Madam Raghupathy,† Hendrik Wiebeler,† Thomas D. Kühne,† Claudia Felser,‡ and Hossein Mirhosseini∗,† †Dynamics of Condensed Matter and Center for Sustainable Systems Design, Department of Chemistry, University of Paderborn, Warburger Str. 100, D–33098 Paderborn, Germany ‡Max-Planck-Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany E-mail: [email protected]

Abstract

counterparts due to the nature of their valence band resulting in a large hole effective mass and poor p-dopability. 6–9 The difficulty in finding a TCO with a low hole effective mass as well as good p-dopability have triggered numerous research efforts. Few binary, ternary, and quaternary p-type TCOs have been synthesized but the majority of them lack one of the prerequisites for an ideal TCM. 10,11 In 1997, Hosono and co-workers 8 identified CuAlO2 as a promising ternary ptype TCO. The authors suggested that the presence of the Cu 3d energy level just above the O 2p energy level results in the raise of the valence band maximum (VBM) of the system which in turn improves hole conductivity. This led to the synthesis and characterization of a series of p-type TCOs based on Cu+ bearing oxides such as CuMO2 (M= Sc, Cr, Co, Ga, In) 12,13 and SrCu2 O2 . 14 These compounds are, however, hampered either by low hole conductivity or poor transparency. 15–18 Hautier and co-workers 9 performed a high-throughput search to find binary and ternary p-type TCOs beyond Cu-based compounds. The authors suggested few earth abundant p-type TCOs such as B6 O and A2 Sn2 O3 (A= K, Na) and less environmentally friendly PbTiO3 and K2 Pb2 O3 compounds. However, the band gaps of A2 Sn2 O3 (A= K, Na) compounds and B6 O are smaller than 3 eV inhibiting the optical transparency.

In this work, we investigated ternary chalcogenide semiconductors to identify promising ptype 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 dopaMaterials Todaybility. Our search led to the identification of seven promising compounds (IrSbS, Ba2 GeSe4 , Ba2 SiSe4 , Ba(BSe3 )2 , VCu3 S4 , NbCu3 Se4 , 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.

Introduction Transparent conducting materials (TCMs) having good electrical conductivity and a wide band gap have received great attentions owing to their applications in different optoelectronic devices. 1–5 The majority of commercialized TCMs are n-type oxide-based semiconductors (TCOs) owing to their small electron effective masses and good n-dopability. In contrast, p-type TCOs lag far behind their n-type

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Hosono and coworkers 14 extended their material design concept to the mixing of chalcogenides (S and Se) with oxygen in Cu-based TCOs. The authors considered layered oxychalcogenides such as LaCuOCh (Ch=S or Se). In this group of compounds, LaCuOS shows a poor mobility, while LaCuOSe has a small band gap. 19–21 Interestingly, layered oxysulfide Sr3 Cu2 Sc2 O5 S2 was found to exhibit a relatively wide band gap (3.1 eV) and a hole mobility that is higher than the typical values for copper-based compounds. 22 Hautier and co-workers also screened oxychalcogenides beyond Cu-based compounds and found ZrOS and HfOS to be promising compounds. These compounds were found to have large hole effective masses suppressing hole conductivity. 9 Similarly, Sarmadian et. al. performed first-principles based high-throughput calculations to screen binary-quaternary oxychalcogenides. 23 The authors found four promising compounds X2 SeO2 (X = La, Pr, Nd, and Gd) that have large band gaps and low hole effective masses. Similarly, Yim et. al. performed high-throughput screening to identify p-type transparent materials and found La2 O2 Te and CuLiO to be promising p-type compounds. 13 While existing studies so far focused on the screening of oxides, layered oxychalcogenides, delafossites, and oxyflurochalcogenides, 24–30 there has been no systematic screening of chalcogenides (sulfides, selenides, and tellurides) for p-type TCMs. The choice stems from the primary findings of our previous paper, where we employed high-throughput calculations to screen binary chalcogenides for various opto-electronic applications. 31 We found several promising materials that can be considered as potential TCM candidates. However, it is known that binary chalcogenides are thermodynamically unstable. In order to overcome this problem, in this study we extended our materials screening to ternary chalcogenides. We selected compounds that satisfy our screening criteria from the Materials Project database (MPD). 32 We found seven promising ternary chalcogenides with a large band gap, a low hole effective mass, and good p-dopability. We also calculated the branch point energy and optical

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absorption spectra for our promising ternary chalcogenides.

Methodology Computational Details All calculations were performed within the framework of density functional theory using the Vienna Ab-initio Software Package (VASP). 33 We used projector augmented wave (PAW) pseudopotentials with a plane-wave cutoff of 500 eV. 34 The Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation was employed for the exchangecorrelation potential. 35 All atomic structures were considered to be relaxed when the residual force on each atom was less than 0.01 eV/˚ A. Brillouin zone integration was performed on a Monkhorst k-point mesh. 36 We adapted the kpoint mesh of each supercell to maintain a constant k-point density for each system. The electronic structures for the selected compounds were calculated using the HSE06 screened hybrid functional. 37 For modeling the point defects we used the PyCDT toolkit, 38 which automatically creates the files for the bulk, dielectric, and defects. Defect formation energies and corresponding charge transition levels were calculated for large supercells containing at least 128 atoms in order to minimize finite-size effects. The defect formation energy is calculated as ∆Ef =Etot (D, q) − Etot (bulk) X − ni µ0i + ∆µi

(1)

i

q + q EVBM + µe + ∆ν0/b + Ecorr , where Etot (D, q) and Etot (bulk) are the potential energies of supercells with the defect (D) in charge state q and the bulk supercell (without defects), respectively. The number of atoms of species i that is removed from/added to the system is indicated by ni while µ0i is the associated chemical potential of species i in the native elemental state. The thermodynamic limits to the chemical potentials were computed by determining the stability region for all the competing


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Matminer package. 43–46 The optical absorption spectra was computed for the most promising pdopable materials from HSE calculations using the random phase approxiMaterials Todaymation. 47

phases with respect to the reference structure. The thermodynamic limit of the chemical potential of species i is indicated by ∆µi . EVBM is the valence band maximum of the bulk, µe is the Fermi energy position (electron chemical potential), which varies from 0 to the band gap of the system, and ∆ν0/b represents the correction q term for the electrostatic alignment. Ecorr represents the correction term for the total energy when the system is charged. It is calculated by the approach proposed by Freysoldt et. al. 39 / Kumagai et. al. 40 depending on the isotropy of the system. The details of this method are discussed in Ref. 38 The p-type dopability of compounds can be roughly estimated by determining the branch point energy (BPE). The BPE corresponds to the energy at which the character of defect states induced in the gap changes predominantly from donor to acceptor. 23,41,42 The formation of acceptor (donor) defect states in the gap depends primarily on the position of this energy with respect to the band edges. 30 Since we are searching for p-type TCMs, the important condition to favor p-type dopability is a BPE close to the VBM. When the BPE lies in the middle of the gap three possibilities are open: the compound may be either p- or n-type dopable, or even ambipolar. In general, accurate defect calculations are required to draw reliable conclusions on the dopability of a compound; the calculations that we performed in this work. The BPE can be approximated as the average of the high lying valence bands and low lying conduction bands as reported by Schleife et. al. 41 and is calculated as " # NV B NCB 1 X 1 X 1 X εi (k)+ εj (k) , εBP = 2NK k NVB i NCB j

Database Screening In this study, we performed a high-throughput computational search to identify the most promising p-type TCM candidates. Our screening procedure is outlined in Figure 1. More than 69,000 inorganic compounds are available in the MPD. Among them, the total number of ternary chalcogenides was found to be 3376 compounds. Ternary chalcogenides having Ax By Cz formula were considered here, where A and B are cationic counterparts (Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, In, Sn, Sb, Ba, W, Re, Os, Ir, Pt, Au, Tl, Bi) and C is either S, Se or Te. The number of compounds was reduced to 763 when we considered the most stable compounds, i.e. Ehull = 0, where Ehull is the energy released by decomposing a compound into other stable compounds. 48 From this list, we selected those compounds having a PBE band gap (Eg ) larger than 1 eV and a total number of 373 compounds were available. The mean hole effective mass screening criterion (m∗h ≤ 1) was further applied on these 373 compounds which resulted in 63 compounds. The hole effective mass values, calculated by the BoltzTraP code, 49 were taken from the Dryad database. 50,51 Our final list consists of only 34 compounds whose HSE band gaps fall between 3.0 eV and 4.3 eV. We show the number of sulfides, selenides, and tellurides found at each step in Figure S1. The HSE band gaps, hole effective masses in different directions and the corresponding harmonic mean hole effective masses for these 34 compounds are listed in the supporting information (see Table S1). Finally, we evaluated the role of intrinsic and extrinsic defects for all 34 compounds to determine p-dopability.

(2) where Nk is the number of k points in the Brillouin zone, εi (k) denotes the ith highest valence band at wave vector k, which is sampled up to i = NV B , whereas εj (k) denotes the jth lowest conduction band at wave vector k, which is sampled up to j = NCB . The BPE was evaluated from the HSE band structures using the


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Figure 1: Schematic workflow for the screening of materials from the MPD.

Results and Discussion

dopable compound, a region of the phase diagram should be selected for which the formation energies of detrimental defects are higher than those of beneficial defects. Hence, we calculated the defect formation energies for all regions of the phase diagram.

Defect Physics A wide band gap and a low hole effective mass are the primary requirements for a highperformance p-type TCM. However, the plausibility of generating holes in the valence band is not guaranteed for the compounds that satisfy the band gap size and effective mass criteria. Hence, it is necessary to investigate the role of defects physics to identify the detrimental intrinsic defects as well as extrinsic dopants. In binary chalcogenides, the formation of anion vacancies was found to be detrimental for pdopability. However, it is evident from our results that for ternary chalcogenides, in addition to anion vacancies, antisites may also hinder p-dopability. On the other hand, the formation of cation vacancies are always beneficial for p-type conductivity. It is poMaterials Todayssible to control the formation of defects by tuning the chemical potential of the constituent elements during the synthesis. To have a p-

Table 1: Promising compounds, their symmetries, HSE band gaps, and harmonic mean hole effective masses. The nature of the band gaps are given as a superscript, where d and id stand for direct and indirect band gap, respectively. Compound Space group EHSE (eV) m∗h (me ) g RbAu3 Se2 RbAuSe KAuSe IrSbS VCu3 S4 CuBS2 NbCu3 Se4 Ba(BSe3 )2 Ba2 SiSe4 Ba2 GeSe4


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P3m1 Cmcm Cmcm P21 3 P43m I42d P43m Cmce P21 /m P21 /m

3.18id 3.40id 3.42id 3.08id 3.68id 3.41d 3.13id 3.53id 3.96 d 3.01d

0.63 1.0 1.0 0.39 0.93 1.0 0.82 0.78 0.75 0.60

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Among the 34 chalcogenides, only few compounds were found to uphold intrinsic defects, see Table 1. For example, RbAu3 Se2 has a wide band gap and a low mean hole effective mass. From the defect calculations (AuSe-Se region), we observed that VacRb and VacAu defects have low formation energies (see Figure S2). These vacancies introduce holes in the valence band leading to an enhanced hole conductivity. The similar stoichiometric compound, RbAuSe has a band gap and a mean hole effective mass that are larger than those of RbAu3 Se2 . In RbAuSe, the formation of VacRb defects is energetically favorable compared to other intrinsic defects (Rb2 Se3 - RbSe region) (see Figure S3). Similar to RbAu3 Se2 , the formation of VacRb in RbAuSe increases the hole concentration. VacAu is also beneficial for hole conductivity but it has a higher formation energy compared to VacRb . In KAuSe, the formation energy of AuK is low compared to all other defects (AuSe-KAuSe2 region), but it stays neutral for all values of µe (see Figure S4). Similar to the previous compounds, the cation vacancies (VacK and VacAu ) have relatively low formation energies and are acceptor defects. These results show that the formation of cation vacancies are energetically favorable and are beneficial for hole conductivity in these compounds. An imperative prerequisite for a high performance p-type TCM is the plausibility of doping with extrinsic dopants. Regardless of the intrinsic defects, a TCM must be doped to enhance its free carrier density . Hence, we doped the aforementioned compounds with Pt as an extrinsic dopant. However, the formation energies of PtAu substitutional defects were high compared to those of detrimental intrinsic defects. That means, these compounds cannot be doped by Pt and might be used as a p-type TCM without external dopants. It should be noted that our findings cannot rule out the possibility of doping aforementioned compounds with other dopants. In the following sections, we discuss the most promising p-type TCM candidates that can be doped by extrinsic dopants for sulfideand selenide-based compounds separately. Our screening and doping criteria led to the iden-

tification of seven promising candidates with good p-type dopability (see Table 1). The defect physics and optical properties of these compounds are discussed as well. Sulfide-based compounds Among the 15 sulfide-based compounds, only 3 of them (IrSbS, VCu3 S4 , and CuBS2 ) exhibited p-type dopability. IrSbS and VCu3 S4 have cubic crystal structures, whereas CuBS2 belongs to the tetragonal family and has an anisotropic nature compared to IrSbS and VCu3 S4 . Regarding the electronic structure, while IrSbS and VCu3 S4 have indirect band gaps, CuBS2 has a direct band gap. The top of the valence band is observed between the M and Γ points for IrSbS, at R for VCu3 S4 , and at the Γ point for CuBS2 . Moreover, the top of the valence band of these three compounds has a dominant d character along with a weak p character. The computed defect formation energies for IrSbS (Ir2 S3 - IrS2 region) are shown in Figure 2a. Our defect calculations show that apart from SSb , other intrinsic defects have relatively high formation energies when the Fermi level is close to the VBM. Therefore, the role of substitutional dopants was explored. We found that the SnSb substitutional defect has a lower formation energy than SSb and acts as a shallow acceptor (see Figure 2a). In addition, SnIr that acts as a hole killer defect has a higher formation energy compared to SnSb . Therefore, IrSbS can be doped by Sn to increase the hole concentration. We also calculated the BPE for the IrSbS bulk. A comparison was done with La2 SeO2 , which was found to be a good p-type TCM candidate. From Figure 3, it is evident that the BPE is close to the VBM, which favors p-type doping in IrSbS. We also calculated the optical absorption spectra for IrSbS. For the incident light polarized along all directions, the absorption peak is formed at 3.2 eV (see Figure S8), which is 0.12 eV greater than the fundamental gap. The defect formation energies for VCu3 S4 under V-poor conditions (CuS-CuS2 region) are shown in Figure 2b. Among all intrinsic defects,


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Figure 2: Defect formation energies of sulfides and selenides as a function of the electron chemical potential (µe ) under thermodynamic limiting conditions to avoid the formation of competing phases (see text). Only the defects that have low formation energy (≤ 3 eV) are shown here. The dashed vertical line indicates the calculated PBE band gap.

Figure 3: Branch point energy, valence band maximum and conduction band minimum of our promising compounds VacCu (acceptor) and Cuitet,S4 (donor) have the lowest formation energies when the Fermi level is close to the VBM. By increasing the electron chemical potential, the formation energy of Cuitet,S4 increases. Regarding the dopants, we observed that the TiV substitutional defect has a lower formation energy compared to VacCu and Cuitet,S4 (see Figure 2b). Moreover, TiV is

an acceptor defect that can introduce holes in the valence band. The branch point calculations show that the BPE falls in the middle of the band gap and therefore might favor p-type doping. The optical absorption peak calculated for VCu3 S4 is 3.68 eV (see Figure S8), which is similar to the fundamental band gap. For CuBS2 , we calculated the defect forma-


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tion energies under Cu-poor conditions (B2 S3 BS2 region). Figure S5 shows that when the Fermi energy is close to the VBM, acceptor defects like VacCu and CuB form and increase the hole concentration. The behavior of VacCu defects in CuBS2 are similar to those observed in Cu2 O 11 and CuAlO2 . 8 Among extrinsic dopants, Zn is found to be a good dopant for increasing the hole concentration in CuBS2 . ZnB has a low formation energy and is negatively charged (acceptor) for all values of the electron chemical potential. The BPE calculated for CuBS2 lies close to the conduction band, which might hinder p-type dopability. The optical absorption spectra calculated for CuBS2 is anisotropic. The average optical band gap is 3.43 eV that is close the the fundamental band gap (3.41 eV) (see Figure S8). Among the sulfide-based compounds, IrSbS and VCu3 S4 were found to be comparatively more promising than CuBS2 .

mental for hole conductivity, VacCu is an acceptor defect that increases the hole concentration. The role of extrinsic dopants was explored with Zr as a dopant. We found that the ZrNb defect acts as an acceptor defect and has a lower formation energy compared to CuNb and Cuitet,Se4 intrinsic defects. From Figure 3 it is evident that the BPE is closer to the VBM rather than the CBM, which favors p-type doping. Since NbCu3 Se4 is a cubic compound, the incident light polarized along all directions shows similar absorption peaks at 3.2 eV (see Figure S8), which is 0.07 eV greater than the fundamental gap. Ba(BSe3 )2 is another candidate for which the defect formation energies were computed (Ba2 B4 Se3 -Ba7 B4 Se13 region). Among the intrinsic defects, VacSe and Seitet,Ba have low formation energies. While VacSe stays neutral for the small values of the electron chemical potential, Seitet,Ba acts as a deep donor and is detrimental for hole conductivity (see Figure 2c). The substitutional BeB defect had a rather low formation energy and was found to improve the hole conductivity in Ba(BSe3 )2 . The BPE calculated for Ba(BSe3 )2 falls in the middle of the band gap indicating it might be p-dopable. The average optical absorption peak calculated for Ba(BSe3 )2 is 4.01 eV (see Figure S8), which is 0.48 eV larger than the fundamental band gap. Ba2 GeSe4 and Ba2 SiSe4 compounds are anisotropic in nature similar to CuBS2 . All intrinsic defects are computed under Ge-poor conditions for Ba2 GeSe4 and Si-poor conditions for Ba2 SiSe4 . Most of the intrinsic defects in Ba2 SiSe4 have high formation energies (see Figure 2d). Among them, VacSi and Sei have relatively low formation energies. Both defects act as a donor defect that can hinder p-type dopability in Ba2 SiSe4 . Regarding Ba2 GeSe4 , most of the defects with low formation energies stay neutral (see Figure S7). For these two compounds substitutional defects were explored to find a proper extrinsic dopant. Substitutional defects such as AlSi in Ba2 SiSe4 and GaGe in Ba2 GeSe4 have relatively low formation energies and are acceptor defects. BPE calculations show that the BPEs of these two compounds fall in the middle of the band gaps indicating

Selenide-based compounds Among the 16 selenium-based compounds, only 4 compounds (NbCu3 Se4 , Ba(BSe3 )2 , Ba2 GeSe4 , and Ba2 SiSe4 ) were found to exhibit p-type dopability. NbCu3 Se4 has a cubic crystal structure, whereas Ba2 GeSe4 and Ba2 SiSe4 belongs to the monoclinic family, and Ba(BSe3 )2 belongs to the orthorhombic family. The electronic structures of NbCu3 Se4 and Ba(BSe3 )2 show an indirect band gap similar to VCu3 S4 , whereas Ba2 GeSe4 and Ba2 SiSe4 have direct band gaps. The top of the valence band is observed at R for NbCu3 Se4 , at the Γ point for Ba2 GeSe4 and Ba2 SiSe4 , and at Y for Ba(BSe3 )2 . The top of the valence band for NbCu3 Se4 shows a dominant d character (Cu for NbCu3 Se4 ) with a weak p character from Se, whereas reverse trends are observed for Ba(BSe3 )2 , Ba2 GeSe4 and Ba2 SiSe4 (a dominant p character from Se). For NbCu3 Se4 , the formation energies for intrinsic defects were computed under Nb-poor conditions (CuSe-CuSe2 region). The defect calculations show low formation energies for CuNb , Cuitet,Se4 , and VacCu intrinsic defects (Figure S6). While CuNb and Cuitet,Se4 are detri-


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that these two compounds might be p-dopable. Since these compounds have anisotropic atomic structures, a strong anisotropic optical absorption was probed for both compounds. The average absorption peak is formed at 3.32 eV for Ba2 GeSe4 and 4.23 eV for Ba2 SiSe4 . The optical band gaps are 0.31 eV and 0.27 eV larger than the fundamental bands gap of Ba2 GeSe4 and Ba2 SiSe4 , respectively.

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the charge transfer from a weekly electronegative element (here K and Rb). This results in a lower coordination number for Au (2) and a linear Se-Au-Se bond angle. The linearly coordinated Au atoms in return give raise to the stronger hybridization of anion and cation states. 53 It is also noted that the anions have a tetrahedral coordination in these compounds. For Ba-based compounds, on the other hand, the tetrahedral coordination of anions was not observed. The strong localization of the upper edge of the valence band stems mainly from relatively localized Se 4p (with a small contribution of Ba 4d) leading to a less disperse valence band (see Figures S11). The counter cation (B, Si and Ge) states are low in energy and do not contribute to the valence band. One can expect a lower effective mass for Ba2 GeSe4 in comparison with Ba2 SiSe4 owing to the larger angles for Ba-Se-Ge (174◦ ) compared to Ba-Se-Si angles (164◦ ). 53 The low hole effective mass of IrSbS stems form the presence of the Ir 5d states in the valence band (see Figures S12). Similar to CuCrO2 that has a linear Cr–O–Cr bond angle, 54 IrSbS has a wide Sb–Ir–S bond angle (174◦ ) that increases the hybridization of Ir 5d and anions p states. IrSbS has the lowest effective mass among other compounds. If the presence of Ir atoms makes IrSbS interesting, more Ir-based compounds (phosphides and nitrides) have to be studied to draw a final conclusion. An overview of defect calculations shows the following trends: the formation of Cu-defects (vacancies, antisites, and interstitials) are found to influence the p-dopability of Cu-based compounds. Among intrinsic defects, VCu is the most common defect that acts as a shallow acceptor leading to enhanced p-type conductivity. This makes Cu-based compounds promising for different opto-electronic applications. For Babased compounds and IrSbS, anion defects (vacancies and interstitials) are found to form more easily than other intrinsic defects. Anion vacancies are hole-killer defects (donor defects) that might prevent p-type dopability. However, most of these defects have relatively high formation energies. The high formation energies for anion vacancies provide the possibility of dop-

Discussion and Conclusions To understand the reasons for the low hole effective masses of our promising compounds, we analyzed the relation between their atomic and electronic structures. Hosono and co-workers 14 proposed two primary requirements for improving the p-type conductivity of TCOs: the localization behavior in the valance band can be reduced by (i) the tetrahedral coordination of oxide ions and (ii) the hybridization of the O 2p states with the Cu closed-shell 3d states. To study the effect of atomic structures on electronic structures we characterized the valence bands of our compounds by calculating atomicand orbital-projected density of states. All Cu-based compounds were found to have tetrahedral-coordinated anions that reduces the localization of anion orbitals. In addition, the maximum coordination number that is expected for Cu atoms in Cu-based chalcogenides is observed. 52 For Cu-based compounds, the disperse valence band originates from the hybridization of the Cu 3d shell with the 4p or 3p orbitals of the counter anions (see Figures S10). The valence band dispersion, however, is not the same in all directions for CuBS2 owing to its anisotropic atomic structure. Although VCu3 S4 and NbCu3 Se4 have the same atomic structures, the smaller hole effective mass of NbCu3 Se4 arises from the enhanced hybridization of Cu 3d with Se 4p in comparison to Cu 3d with S 3p. For Au-based compounds, the low hole effective mass stems from the overlap of Au and Se orbitals. This is in the line with the argument of Gaudin et al. 52 that states the polarization of the chalcogenides can be raised through


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• List of compounds, their HSE band gaps, hole effective masses along different directions, and the associated harmonic average hole effective masses

ing these compounds with external dopants. In short, high-throughput DFT-based calculations were performed to identify potential ptype TCMs for different opto-electronic applications. Ternary chalcogenides were considered for this study. From a large dataset (more than 69000 compounds), we studied 3376 ternary chalcogenides found in the MPD. Finally, our material screening criteria were based on a wide > 3.0 eV) and a low hole efband gap (EHSE g ∗ fective mass (mh ≤ 1). A total of 34 compounds were found to satisfy these criteria. Further analysis on the p-type dopability of these compounds suggested seven promising p-type transparent chalcogenides that have not been reported before. In addition, the branch point energy and optical absorption spectrum were calculated for these compounds. Among seven promising compounds, Sn doped IrSbS and Zr doped NbCu3 Se4 are expected to perform better than others based on our screening criteria. We hope that these results will persuade experimentalist to synthesize some of these compounds as an alternative p-type TCM.

• Formation energies of point defects for various compounds • Optical absorption spectra for S- and Sebased compounds • Atomic- and orbital-projected density of states for promising compounds

References (1) Granqvist, C. G. Transparent Conductors as Solar Energy Materials: A Panoramic Review. Sol. Energy Mater. Sol. Cells 2007, 91, 1529–1598. (2) Ellmer, K. Past Achievements and Future Challenges in the Development of Optically Transparent Electrodes. Nat. Photonics 2012, 6, 809–817. (3) Fortunato, E.; Ginley, D.; Hosono, H.; Paine, D. C. Transparent Conducting Oxides for Photovoltaics. MRS Bull. 2007, 32, 242–247.

Acknowledgement The authors would like to acknowledge financial support from the German Bundesministerium f¨ ur Wirtschaft und Energie (BMWi) for the speedCIGS project (0324095C). The authors gratefully acknowledge the Gauss Centre for Supercomputing e.V. (www.gausscentre.eu) for funding this project by providing computing time on the GCS Supercomputer SuperMUC at the Leibniz Supercomputing Centre (www.lrz.de). The authors would like to acknowledge the Paderborn Center for Parallel Computing (PC2 ) (https://pc2.uni-paderborn.de/hpcservices/available-systems/oculus/) supercomputing time on OCuLUS.

(4) E., F.; P., B.; R., M. Oxide Semiconductor Thin-Film Transistors: A Review of Recent Advances. Adv. Mater 2012, 24, 2945–2986. (5) Ginley, D.; Hosono, H.; Paine, D. C. Handbook of Transparent Conductors, 3rd ed.; Springer: New York, 2011. (6) Ohta, H.; Hosono, H. Transparent Oxide Optoelectronics. Mater. Today 2004, 7, 42 – 51. (7) Banerjee, A.; Chattopadhyay, K. Recent Developments in the Emerging Field of Crystalline P-Type Transparent Conducting Oxide Thin Films. Prog. Cryst. Growth Charact. Mater. 2005, 50, 52–105.

Supporting Information • Number of sulfides, selenides, and tellurides for each step of the screening procedure


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Database Screening of Ternary Chalcogenides for P-type Transparent

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