First-principles DFT insights into the structural, elastic, and optoelectronic properties ofαandβ-ZnP₂: implications for photovoltaic applications

Abstract

Binary II-V semiconductors are highly optically active materials, possess high intrinsic mechanical and chemical durability, and have electronic properties ideal for optoelectronic applications. Among them, zinc diphosphide (ZnP 2) is a promising earth-abundant absorber material for solar energy conversion. We have investigated the structural, mechanical, and optoelectronic properties of both the tetragonal (α) and monoclinic (β) phases of ZnP 2 using standard, Hubbard-corrected and screened hybrid density functional theory methods. Through the analysis of bond character, band gap nature, and absorption spectra, we show that there exist two polymorphs of the β phase (denoted as β 1 and β 2) with distinct differences in the photovoltaic potential. While β 1 exhibits the characteristics of metallic compounds, β 2 is a semiconductor with predicted thin-film photovoltaic absorbing efficiency of almost 10%. The α phase is anticipated to be an indirect gap material with a calculated efficiency limited to only 1%. We have also analysed and gained insights into the electron localization function, projected density of states and projected crystal orbital Hamilton populations for the analogue bonds between the α and β-ZnP 2. In light of these calculations, a number of previous discrepancies have been solved and a solid ground for future employment of zinc diphosphides in photovoltaics has been established.

Raman and infrared phonons in tetragonal ZnP2and CdP2crystals: a density functional study

“…The lattice was optimized until residual forces on atoms in their equilibrium positions not exceeded 5 meV Å −1 . The results of this optimization are summarized in table 1. In agreement with earlier theoretical studies [7], both ZnP 2 and CdP 2 clearly shown a non-metallic behaviour. This Table 1.…”

“…Metal atoms and phosphorous occupy general position (8b) within the unit cell. Experimentally determined lattice parameters are a = b = 0.50586 (7) nm and c = 1.8506(4) nm for ZnP 2 and a = b = 0.52768 (7) nm and c = 1.9753(3) nm for CdP 2 [6]. Table 1 summarizes experimental and DFT-calculated, as is described below, positions of atoms within ZnP 2 unit cell.…”

“…Even though basic physical properties of ZnP 2 and CdP 2 crystals are known for decades [4,5], there are still a number of unresolved issues. More recently detail theoretical study of electronic band structure of these materials [6,7] as well as high pressure dynamic and thermodynamic properties [8] have been reported. Among practical applications of binary zinc phosphides we mention C-modified ZnP 2 and Zn 3 P 2 composites, which are used as high performance sodium-ion battery anodes [9].…”

Insights from density functional theory calculations into the effects of the adsorption and dissociation of water on the surface properties of zinc diphosphide (ZnP2) nanocrystals

“…The valence band of β-ZnP2 is found to be dominated by the electronic states of the Zn-pd and P-p orbitals, whereas the conduction band is composed mainly of the Zn-d orbitals. 24 The relaxed bulk β-ZnP2 structure was employed to create the seven low-Miller index surfaces -(001), ( 010), ( 100), ( 011), ( 101), ( 110) and (111) and considering all possible non-dipolar terminations. Each surface was fully relaxed to predict the lowest-energy structures, surface energies, and order of stability.…”

“…23 In our recent study, we have employed the screened hybrid approach to determine the optoelectronic and dielectric properties of the α-ZnP2 and β-ZnP2 phases, and predicted a thin-film PV absorbing efficiency of almost 10% for β-ZnP2. 24 As surfaces and interfaces play an important role in the rational design of tandem solar cells, it is important to gain an atomic-level understanding of their structures and composition, whereas the relative stabilities of β-ZnP2 surfaces and possible changes in their electronic structures and crystal morphology upon prolonged exposure to wet conditions should also be elucidated for practical applications. Low surface stability in the presence of moisture and oxygen [10][11] remains a major problem that severely limits commercial fabrication of efficient zinc-based PV materials.…”