Quasi-direct Band Gap Research Articles

Adjustable electronic properties of PtSe2/HfS2 heterostructures via strain engineering

2D PtSe2 Semiconductors are promising for the development of next-generation infrared photodetectors. However, the performance of 2D PtSe2 photodetectors is largely limited by their small detection range (due to large bandgap) and poor light absorption (due to indirect bandgap). To overcome these limitations, vertical PtSe2/HfS2 van der Waals heterostructures were constructed and the rule of their electronic property changes under strain was investigated systematically. The heterostructures exhibit type-II band alignment and a smaller bandgap (E(PtSe2) − E(PtSe2/HfS2) = 1.19 eV), which is beneficial for the separation of carriers and the application in infrared photodetectors. Moreover, the stacking configurations do not change the type of band alignment, and the bandgap of different stackings are similar, which proves that the electronic properties of the heterojunction are stable. Among the six stackings, AA stacking is the most stable structure, which can be modified to adapt to different working conditions under strain. It exhibits a quasi-direct bandgap (0.14 eV) under the condition of 11% reverse strain applied in × and Y directions respectively, which is suitable for preparing photoelectric devices working in the middle and far infrared regime. These findings provide a theoretical basis for the application of PtSe2/HfS2 heterojunction in next-generation infrared photodetectors.

A superhard orthorhombic carbon allotrope

An allotrope of carbon called C24-Q is proposed and its structure, electronic, mechanic properties and stability are investigated elaborately by means of density functional theory (DFT). The elastic constants and phonon spectrum of C24-Q indicate that C24-Q has mechanical stability and dynamic stability, respectively. There are two kinds of carbon atoms in different positions of C24-Q in space, and the crystal structure of C24-Q shows that it has 4-, 6-, and 8-membered rings. The relative enthalpy of C24-Q is smaller than that of T-carbon. C24-Q has a larger Young's modulus and shear modulus than T-carbon and C24-D. C24-Q also shows mechanical anisotropy. Furthermore, the mechanical anisotropy in Young's modulus, shear modulus and Poisson's ratio of C24-Q in seven principal planes are also considered, and it was found that C24-Q has smaller anisotropy differences than C24-D and C24-I. The hardness of this proposed novel carbon structure is 50.31 GPa, which reveals that C24-Q has superhard characteristics. More importantly, it is derived from the electronic band structure of C24-Q that it is a semiconductor material with a quasi-direct band gap of 4.432 eV.

Comprehensive Screening of Halogen-Containing Oxide Double Perovskites A2BXO6 (X = Cl, Br, and I) for Photovoltaic Applications.

The new halogen-containing oxide double perovskites A2BXO6 (X = Cl, Br, and I) have attracted much attention because of their superb electronic properties in halide double perovskites and their high stability in oxide double perovskites. Herein, 408 A2BXO6 double perovskites have been systematically screened by high-throughput computation. Refer to the empirical structural factors phase diagram (t-u), which uses large-scale first-principles calculations. Fourteen stable perovskites are finally confirmed; moreover, 11 of them have never been reported before. Our results show that Ba2AgIO6 and Sr2AgIO6 are the most preferable candidates for photovoltaic applications, of which Sr2AgIO6 has balanceable electron and hole effective masses, a quasi-direct band gap, and strong optical absorption. Importantly, Sr2AgIO6 was successfully synthesized by the solution method. Our work enriches the family of double perovskites, and the tentative experimental evidence undoubtedly hints at their great potential applications in the near future.

Electrical properties of 2H-Si microwire grown by mixed-source hydride vapor phase epitaxy

Hexagonal 2H polytypes of Si (2H-Si) exhibit promising mechanical and optical properties owing to their crystal structures with quasi-direct bandgap characteristics. However, few studies have investigated the electrical properties of 2H-Si semiconductors. In this study, we used a hot-probe measurement to determine the doping type of 2H-Si microwires (MWs) prepared by hydride vapor-phase epitaxy (HVPE). It was found that the 2H-Si MWs had unintentional n-type characteristics. For the first time, a heterojunction PN diode with n-type 2H-Si MW and p-type Si (100) was fabricated. According to the current–voltage and capacitance–voltage measurements, the n-type doping concentration of the unintentionally doped 2H-Si MWs was 4.3–9.5 × 1015 cm−3 and the electron mobility was 260–580 cm2/V·s.

Quasiparticle, optical, and excitonic properties of layer dependent GaSe

The two-dimensional (2D) optical absorbance and complex optical conductivity can well define the optical properties of 2D materials and they are fundamental for the design and manufacture of optoelectronic devices. In this work, quasiparticle electronic structure, optical absorbance and complex optical conductivity of 1-layer to 3-layer GaSe are studied by the self-energy GW0 method and the Bethe–Salpeter equation (BSE). Relative to bulk GaSe with a direct bandgap, our calculation results show that three kinds of two-dimensional GaSe are all quasi-direct band gap semiconductors. Due to the exciton effect, their optical absorbance spectrums are red-shifted, and the absorption intensity increases rapidly near the band gap. The exciton binding energies of 1-layer to 3-layer GaSe are increased significantly with respect to bulk GaSe.

Ternary pentagonal BNSi monolayer: Two-dimensional structure with potentially high carrier mobility and strong excitonic effects for photocatalytic applications

In recent years many attempts have been made to discover new types of two-dimensional (2D) nanostructures with novel properties beyond the hexagonal crystals. The prediction of pentagraphene has sparked a great deal of research interest to investigate 2D pentagonal systems. In line with these efforts, in this paper, we propose a 2D ternary pentagonal monolayer of BNSi (penta-BNSi) and systematically investigate its structural, vibrational, mechanical, piezoelectric, electronic, photocatalytic, and optical properties by performing first-principles methods. We verify the stability of the penta-BNSi monolayer from the dynamical, thermal, and mechanical aspects based on phonon dispersion, ab initio molecular dynamics, and elastic tensor analysis, respectively. The mechanical properties are examined by calculating in-plane stiffness $({Y}_{2\mathrm{D}})$, Poisson's ratio $(\ensuremath{\nu})$, and ultimate tensile strength and penta-BNSi is found to be soft and ductile. The electronic structure and electronic transport calculations indicate that the penta-BNSi monolayer possesses a quasidirect band gap and anisotropic, potentially high carrier mobility. Due to the noncentral symmetric character and semiconducting feature, an intrinsic piezoelectric response emerges in the structure. In addition, penta-BNSi has a suitable band gap as well as proper band edge positions for photocatalytic water splitting within practical pH levels. The analysis of optical properties, including many-body effects, points out strong exciton binding and high light absorption in the visible and near-UV parts of the spectrum. Our findings not only expand the family of 2D pentagonal materials but also uncover an ideal ultrathin material for photocatalytic applications.

Insights into the growth of hexagonal Si crystals using Al-based nano absorber

Although hexagonal (2H) silicon (Si) semiconductors exhibit excellent optical properties owing to their quasi-direct bandgap, their growth conditions, which require extremely high pressures, preclude their widespread use in industrial applications. The current study, therefore, proposes a novel approach for the facile growth of hexagonal Si at atmospheric pressure via a unique phenomenon known as Al-based nano absorber. A mixed-source hydride vapor phase epitaxy (HVPE) method was used for the growth of the hexagonal Si single crystals employing a rapid interaction between GaCl3, AlCl, and SiCln gases at a high temperature of 1200 °C using a source mixture of Ga, Al, and Si. In this process, the Al-based nano absorber was formed, which resulted in the absorbance of Si atoms, rather than the growth of Al-based nano absorber, to form the Si crystals due to the subsequent lack of GaCl3 and AlCl sources. The hexagonal Si structure of these Si crystals was confirmed using field emission scanning electron microscopy, high-resolution x-ray diffraction spectroscopy, and Raman spectroscopy. Thus, the current study establishes atmospheric pressure mixed-source HVPE as a facile approach for growing various allotropic crystals such as Si, C, or Ge via absorption of other atoms by an Al-based nano absorber.

Two-dimensional tetrahexagonal CX2 ( X = P, As, Sb) semiconductors for photocatalytic water splitting under visible light

In this paper, we introduce a family of two-dimensional group-V carbides with an ordered sequence of tetragons and hexagons (th-$\mathrm{C}{X}_{2}$, where $X=\text{P}$, As, and Sb). We demonstrate that th-$\mathrm{C}{X}_{2}$ monolayers exhibit robust energetic, dynamical, thermal, and mechanical stability. Our calculations show that the intrinsic structural anisotropy of the th-$\mathrm{C}{X}_{2}$ family induces strongly anisotropic mechanical, electronic, and optical behavior. These monolayers offer ultrahigh ultimate tensile strength, comparable with that of graphene, making them suitable for strain engineering of electronic and optical properties. They are semiconductors in nature, where th-${\mathrm{CP}}_{2}$, th-${\mathrm{CAs}}_{2}$, and th-${\mathrm{CSb}}_{2}$ possess quasidirect, direct, and indirect band gaps, respectively. The band gaps of th-${\mathrm{CP}}_{2}$ and th-${\mathrm{CAs}}_{2}$ are wide enough to provide the photogenerated energy required for the splitting of water. Besides, the positions of band edges are in alignment with the water oxidation and reduction potentials. For th-${\mathrm{CSb}}_{2}$, however, the suitable width of the band gap and the appropriate band edge positions for photocatalytic water splitting are achieved by strain engineering. Both indirect-to-direct and direct-to-indirect band gap transitions can be induced in th-$\mathrm{C}{X}_{2}$ compounds through strain engineering. The th-$\mathrm{C}{X}_{2}$ monolayers offer anisotropic high charge carrier mobility, which prolongs the average lifetime of charge carrier drift. They have good optical absorption ($\ensuremath{\sim}{10}^{5}$ ${\mathrm{cm}}^{\ensuremath{-}1}$) in the visible and ultraviolet regions of the light spectrum. $G{W}_{0}+$BSE (Bethe-Salpeter equation) calculations reveal that they exhibit strong excitonic effects where the first bright excitonic binding energy is calculated as 0.27, 0.52, and 0.22 eV for th-${\mathrm{CP}}_{2}$, th-${\mathrm{CAs}}_{2}$, and th-${\mathrm{CSb}}_{2}$, respectively. Having all these features in one package, the th-$\mathrm{C}{X}_{2}$ monolayers are among the best candidates for high-performance photocatalytic water splitting.

CeTaN3 and CeNbN3: Prospective Nitride Perovskites with Optimal Photovoltaic Band Gaps

Perovskites constitute an exceptionally tunable materials family with diverse applications in electronics, optoelectronics, energy, and quantum technologies. Out of the thousands of known perovskites, the majority of compounds are oxides, halides, and chalcogenides. In contrast, only two nitride perovskites are currently known. In this work we perform a thorough ab initio computational screening of possible nitride perovskites, and we identify two new compounds, CeNbN3 and CeTaN3, with band gaps in the near-infrared to visible range, depending on temperature. In their room-temperature orthorhombic phase, we predict that both compounds exhibit direct or quasidirect band gaps in the range 1.1–2.0 eV, with the Pnma phases matching the Shockley–Queisser limit for photovoltaic energy conversion efficiency. These compounds are also predicted to be strong light absorbers, with absorption coefficients surpassing those of high-performance semiconductors such as GaAs and CH3NH3PbI3. The present findings reveal a potentially new class of nitride semiconductors with promise for electronics, optoelectronics, and light harvesting and for integration with existing nitride-based lighting technology.

Short Photoluminescence Lifetimes Linked to Crystallite Dimensions, Connectivity, and Perovskite Crystal Phases.

Time-correlated single photon counting has been conducted to gain further insights into the short photoluminescence lifetimes (nanosecond) of lead iodide perovskite (MAPbI3) thin films (∼100 nm). We analyze three different morphologies, compact layer, isolated island, and connected large grain films, from 14 to 300 K using a laser excitation power of 370 nJ/cm2. Lifetime fittings from the Generalized Berberan-Santos decay model range from 0.5 to 6.5 ns, pointing to quasi-direct bandgap emission despite the three different sample strains. The high energy band emission for the isolated-island morphology shows fast recombination rate centers up to 4.8 ns–1, compared to the less than 2 ns–1 for the other two morphologies, similar to that expected in a good quality single crystal of MAPbI3. Low-temperature measurements on samples reflect a huge oscillator strength in this material where the free exciton recombination dominates, explaining the fast lifetimes, the low thermal excitation, and the thermal escape obtained.

Several semiconducting two-dimensional silicon nanosheets assembled from zigzag silicene nanoribbons.

Semiconducting two-dimensional intrinsic silicon nanosheets are ideal materials for many applications in modern industry, since they are the only ones that can match well with previous silicon components. However, such materials are still lacking, especially those with moderate band gaps. In this work, by using first-principles theory, a series of two-dimensional intrinsic silicon nanosheets are assembled from zigzag silicene nanoribbons with different widths. The result shows that all the nanosheets behave as semiconductors, although some of them possess small band gaps of dozens of meV. Two of them, individually assembled from the two narrowest zigzag silicene nanoribbons, possess the largest indirect band gaps of 0.20 and 0.26 eV, respectively. Under low compressive strain, these two nanosheets would turn into quasi-direct or direct band gap semiconductors, and the gaps increase up to 0.62 or 0.54 eV, respectively. Due to the electron transfer from three-fold to four-fold coordinated Si atoms, the charge carriers prefer to transport along the zigzag direction, and electrons and holes transport in the respective Si chains. Interestingly, the investigation of Poisson's ratio reveals that the assembled silicon nanosheets have a negative Poisson's ratio in certain strain ranges if the width n of zigzag silicene nanoribbons is even. This work provides a new approach to design semiconducting silicon nanosheets and benefits to the applications of two-dimensional silicon nanosheets in many electronic and mechanical fields.

The first principle study of structural, mechanical, electronic and optical properties of double halide perovskite K2BI6 (B = Ti, Zr and Hf)

Double halide perovskites have outstanding properties for optoelectronic and renewable energy applications. In the present work, we have analszed the structural, mechanical, electronic and optical properties of K2BI6 (B = Ti, Zr and Hf) using the density functional theory. The results show that these perovskites have good mechanical stability. K2HfI6 is a direct bandgap semiconductor with a bandgap of 3.150 eV. K2TiI6 and K2ZrI6 are indirect bandgap semiconductors with bandgaps of 1.828 and 2.515 eV, respectively, but they can be regarded as quasi-direct bandgap semiconductors. They also show good light absorption properties in the ultraviolet–visible wavelength range. These properties make K2BI6 (B = Ti, Zr and Hf) perovskites good candidates for photovoltaic and optoelectronic applications, such as solar cells, photocatalysts and detectors.

Theoretical Investigations of a BN Polymorph with sp2 + sp3 Hybridizations

The crystal structure, mechanical anisotropy, elastic properties and electronic characteristics, as well as the stability, of P4/m BN are predicted by means of density functional theory. In this work, BN in the P4/m phase demonstrates mechanical and dynamical stability. Compared with the values of bulk B, E and G in the P4/m phase, the B of BN in the P4/m phase is greater than that of dz4 BN, while the G and E of P4/m BN are greater than those of Pnc2 BN and dz4 BN. The ratio of the bulk-to-shear modulus for P4/m BN is less than 1.75 and dz4 BN, dz2 BN and lzlz2 BN, indicating that P4/m BN is more brittle than dz4 BN, dz2 BN and lzlz2 BN. P4/m BN exhibits stronger mechanical anisotropy in G and E than Pbca BN, P42/mnm BN and Pm-3m BN but much weaker mechanical anisotropy than P4/mbm BN, B7N7, B11N11 and B15N15. In addition, P4/m BN is a quasi-direct bandgap semiconductor, and the difference between the direct and the indirect bandgap is 0.008 eV. In order to obtain further characteristics of P4/m BN for future synthetic verification, the X-ray diffraction (XRD) patterns for P4/m BN are also calculated. Given its properties, P4/m BN is a good candidate for photoelectric devices.

Electronic structure and stability of Cs2TiX6 and Cs2ZrX6 (X = Br, I) vacancy ordered double perovskites

Vacancy ordered halide perovskites have been extensively investigated as promising lead-free alternatives to halide perovskites for various opto-electronic applications. Among these, Cs2TiBr6 has been reported as a stable absorber with interesting electronic and optical properties, such as a bandgap in the visible, and long carrier diffusion lengths. Yet, a thorough theoretical analysis of the exhibited properties is still missing in order to further assess its application potential from a material's design point of view. In this Letter, we perform a detailed analysis for the established Ti-based compounds and investigate the less-known materials based on Zr. We discuss in detail their electronic properties and band symmetries, highlight the similarity between the materials in terms of properties, and reveal limits for tuning electronic and optical properties within this family of vacancy ordered double perovskites that share the same electron configuration. We also show the challenges to compute accurate and meaningful quasi-particle corrections at the GW level. Furthermore, we address their chemical stability against different decomposition reaction pathways, identifying stable regions for the formation of all materials, while probing their mechanical stability employing phonon calculations. We predict that Cs2ZrI6, a material practically unexplored to date, shall exhibit a quasi-direct electronic bandgap well within the visible range, the smallest charge carrier effective masses within the Cs2BX6 (B = Ti, Zr; X = Br, I) compounds, and a good chemical stability.

Physical properties of group 14 elements in P2/m phase

Physical properties of J-carbon, J-silicon, and J-germanium (space group: P2/m) were studied by density functional theory calculations. J-germanium was found to be dynamically, mechanically and thermodynamically stable under ambient pressure. The bulk modulus B and the shear modulus G of J-germanium are 55 ​GPa and 41 ​GPa, respectively, slightly greater than those of P42/mnm Ge, hP12 Ge and oC12 Ge. J-carbon, J-silicon, and J-germanium exhibit a larger anisotropy in Young's modulus than do carbon, silicon, and germanium in the diamond phase and also exhibit larger anisotropy in bulk modulus and shear modulus than do the corresponding diamond phase allotropes. J-germanium is a quasi-direct band gap semiconductor material with the band gap of 0.943 ​eV that may be a candidate material for use in photovoltaic devices. The band gap and the minimum thermal conductivity κmin of J-carbon are both greater than those of diamond, and therefore, J-carbon may be a promising candidate material for deep ultraviolet photodetection.

Structure-Composition-Property Relationships in Antiperovskite Nitrides: Guiding a Rational Alloy Design.

The alloy strategy through the A- or X-site is a common method for experimental preparation of high-performance and stable lead-based perovskite solar cells. As one of the important candidates for lead-free and stable photovoltaic absorbers, the inorganic antiperovskite family has recently been reported to exhibit excellent optoelectronic properties. However, the current reports on the design of antiperovskite alloys are rare. In this work, we investigated the previously overlooked electronic property (e.g., conduction band convergence), static dielectric constant, and exciton binding energy in inorganic antiperovskite nitrides by first-principles calculations. Then, we revealed a linear relationship between the tolerance factor and various physical quantities. Guided by the established structure-composition-property relationship in six antiperovskite nitrides X3NA (X2+ = Mg2+, Ca2+, Sr2+; A3- = P3-, As3-, Sb3-, Bi3-), for the first time, we designed a promising antiperovskite alloy Mg3NAs0.5Bi0.5 with a quasi-direct band gap of 1.402 eV. Finally, we made a comprehensive comparison between antiperovskite nitrides and conventional halide perovskites for pointing out the future direction for device applications.

DFT calculation on electronic properties of vacancy-ordered double perovskites Cs2(Ti, Zr, Hf)X6 and their alloys: Potential as light absorbers in solar cells

Electronic properties of Cs2(Ti, Zr, Hf)X6, where X = I, Br, and Cl in vacancy-ordered double perovskite (VODP) structure were studied by using the density functional theory (DFT) calculation with the Heyd–Scuseria–Ernzerhof (HSE) hybrid functional and spin–orbit coupling (SOC). The “quasi-direct bandgap” of these semiconductors was found, indicating the significantly small difference between indirect (Γ-X) and direct (Γ- Γ) bandgaps. The bandgaps of VODP are in the range of 1.08–3.51 eV for Cs2TiX6, 2.63–5.21 eV for Cs2ZrX6, and 3.04–5.65 eV for Cs2HfX6, which could be suitable for a wide range of applications such as solar cells, optoelectronics, and photodetectors. Moreover, the electron contributions to the valence band maximum (VBM) and conduction band minimum (CBM) of VODP are dominated from p-orbital of X-site atoms (I, Br, Cl) and d-orbital of B-site atoms (Ti, Zr, Hf), opening up the opportunity to tune the bandgap by mixing X- or B-site atoms. In this study, we also examined two alloy-systems by mixing B-site atoms, which possess lattice mismatches of less than 1%. We found that by mixing Hf and Zr more than 25% (x greater than 0.25) into Cs2TiI6, the bandgaps of Cs2Ti1-xZrxI6 and Cs2Ti1-xHfxI6 change to the direct type. A fraction of Hf and Zr less than 25% could provide the suitable bandgaps for the light-absorber layer of single junction solar cells, while higher fractions of Zr (25–75%) and Hf (25–50%) could achieve the appropriate bandgap for higher-bandgap materials in tandem solar cells. Additionally, when the relationship between bandgaps and mixing concentration (x) was extracted using Vegard’s law, we found that this relationship aligned well with the x-dependent bowing parameter, b(x), rather than the constant b. Our investigation proved that Cs2(Ti, Zr, Hf)X6 could provide greater benefit than the conventional perovskite (CP) CsBX3 due to their stability, lattice matches, and the wide range of their bandgaps.

On the optical properties and dynamical and mechanical stability of 1T PdSSe, PdSTe, and PdSeTe monolayers under biaxial strain

In this work, the effects of compressive and tensile biaxial strain, applied to monolayered 1T Pd Janus PdSSe, PdSTe, and PdSeTe structures are investigated. For tensile strengths larger than 4%, the valence band maxima no longer occur at the high symmetry Γ point; this phenomenon is accompanied by the emergence of a quasi-direct bandgap, where Dirac-like cones develop for large enough strain. A semiconductor-semimetal phase transition takes place for compressive strain strengths of −8%, −4%, and −2% in PdSSe, PdSTe, and PdSeTe respectively. Phonon dispersion calculations show that the Janus structures, subject to tensile strains, are dynamically stable; yet under compressive strains, they are only stable for values not exceeding −6% in PdSSe, −4% in PdSTe, and −2% in PdSeTe. All structures are mechanically stable except for PdSTe under a 14% tensile strain, registering negative in-plane stiffness constants of −9.36 and −7.62 N/m along the x and y directions respectively. Optical absorption/emission within the infrared region is possible when the materials are exclusively subject to tensile strain. Once the Pd Janus structures are synthesized, the results presented here can serve as a guide for the fabrication of optoelectronic devices of optimal performance.

Optical property of hexagonal (2H) silicon crystal

Hexagonal (2H) silicon (Si) semiconductors have excellent mechanical properties and optically diverse applications due to their structure and quasi-direct bandgap. The 2H-Si has a relatively lower direct band gap of approximately 1.69 eV at the Γ-point in comparison with that of diamond-silicon (i.e. 3.4 eV), but it is not actually a direct bandgap semiconductor. Herein, we report an optical property of wide spectrum light emission in visible and infrared ranges from grown Si crystals with a 2H structure of a 0 = 0.3824 nm, c 0 = 0.6257 nm, and c 0/a 0 = 1.6362 corresponding to theoretical predictions and experimental results. Obtained via high-resolution transmission electron microscopy measurements, the crystal structure of the grown 2H Si possesses the only stable form of the 2H structure with the characteristic quasi-direct bandgap, achieved using mixed-source hydride vapor phase epitaxy at about 1200 °C. Raman, photoluminescence, and electroluminescence spectra, Commission International de l’ Eclairage chromaticity coordinates of light emission, lattice parameters, and the quality of the crystals were evaluated and found to correspond with the predicted results. The reported material has potential applications in optoelectronics.

Direct and quasi-direct band gap of novel Si-Ge alloys in P-3m1 phase

This work investigates the crystal structure, stability, mechanical properties, electronic properties, effective masses, and optical properties of Si-Ge alloys in the P-3m1 phase. The elastic constants and phonon spectra proven that the Si-Ge alloys in the P-3m1 phase have mechanical and dynamic stability. The bulk modulus, shear modulus and Young’s modulus of Si-Ge alloys in the P-3m1 phase decrease with the increase of Ge composition, and the three-dimensional diagram of Young's modulus and effective mass show that the mechanical and transport properties have anisotropy. The Si12Ge12 in the hP24 phase is a quasi-direct band gap semiconductor material with a band gap of 1.081 eV, while the Si30−x Ge x alloy (x = 6, 12, 18, 24) in the hP30 phase are all direct band gap semiconductor materials with the band gaps of 0.541 eV, 0.430 eV, 0.561 eV, and 0.387 eV, respectively. The hP30-Si6Ge24 has a very small effective electron mass. The hP24-Si12Ge12 show excellent absorptive capacity in the visible and infrared region region. Based on this work, Si-Ge alloys in the P-3m1 phase are promising materials for photovoltaic applications.