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In this paper, a systematic investigation of electronic structure and optical properties of quaternary chalcopyrite semiconductors Cu 2 ZnGeS 4 and Cu 2 ZnGeSe 4 in stannite and kesterite structures using the full-potential linearized augmented plane wave method are presented. The electronic structures and related properties of the crystals are studied with density functional theory using modified Becke – Johnson (mBJ) potential. The computed bands and density of states are found to be in good agreement with the available experimental and theoretical results. Important optical properties such as, dielectric functions, absorption spectra, refractivity and reflectivity of the crystals have also been investigated using the mBJ exchange potential. The imaginary parts of dielectric tensor are analyzed in terms of interband transitions. The band gap energies of stannite CuZnGeS 4 (CuZnGeSe 4) and kesterite CuZnGeS 4 (CuZnGeSe 4) compounds are obtained as 1.23 (0.74) eV and 1.52 (1.08) eV, respectively. Present band gap energies and optical parameters show feasibility of the studied materials in photovoltaic and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

A series of novel, low-cost materials SrSnX 2 (X=N, P, Sb, As, Bi) is explored through density functional theory in terms of structural, electronic, and optical properties to underline the usage of these compounds as photo-absorber materials. Within the modified Becke-Johnson exchange-correlation potential, SrSnN 2 shows a direct band gap of 1.94 eV while other materials in the series show a natural intermediate band which supports the two-step optical transition and hence increases the absorption in the visible energy region. Calculated values of the effective mass of electrons, effective densities of conduction, and valence states are found comparable with typical photovoltaic materials (Si and CdTe). We have obtained a high open-circuit voltage of 1.75 V, fill-factor of 0.92 with maximum efficiency of about 23% under one sun condition with a thickness of 10 nm which suggests that SrSnBi 2 stands as a potential candidate for photovoltaics. The calculated band-edges concerning normalizing hydrogen electrode appeal their use as efficient photo-electrocatalyst for water splitting. Overall, we suggest that the natural intermediate band gap-materials are promising candidate for low-cost and efficient photovoltaic and photo-electrocatalytic applications. [ABSTRACT FROM AUTHOR]

Researchers have shown ample concern in the investigation of new potential materials which resembles with required band gap range for photovoltaic applications and hence demonstrates higher conversion rates when exposed to sunlight. Present study is focused towards identifying the effect of M = (Ge, Sn) doping on structural, electronic and optical properties of promising photovoltaic ZnSiP 2 material. All Investigations have been performed using well-established and most precise full potential linearized augmented plane wave method. Detailed realization of pure and doped ZnSi (1 – x) M x P 2 (M = Ge and Sn; 0 ≤ x ≤ 1) have been implemented using highly immaculate Tran- Blaha modified Becke-Johnson (TB-mBJ) exchange and correlation potential. Investigated parameters includes crystal structure, energy bands, density of states, dielectric tensor, absorption, reflectivity and refraction spectra which helps to elaborate complete behavior of these compounds. Energy band gap, attained from TB-mBJ, for pure ZnSiP 2 (1.98 eV) matches precisely with available theoretical and experimental calculations and hence validates accuracy of present computation. This is observed that increase in doping percentage (x = 0.125 to 0.75) of Sn at Si site, results with systematic reduction in band gap (1.96 to 1.81 eV) value which increases possible utilization of this material in photovoltaic applications. On the other hand, reasonable reduction is not observed with Ge doping of similar scale. [ABSTRACT FROM AUTHOR]