Tail state formation in solar cell materials: First principles analyses of zincblende, chalcopyrite, kesterite and hybrid perovskite crystals

Abstract

Tail state formation in solar cell absorbers leads to a detrimental effect on solar cell performance. Nevertheless, the characterization of the band tailing in experimental semiconductor crystals is generally difficult. In this article, to determine the tail state generation in various solar cell materials, we have developed a quite general theoretical scheme in which the experimental Urbach energy is compared with the absorption edge energy derived from density functional theory (DFT) calculation. For this purpose, the absorption spectra of solar cell materials, including CdTe, CuInSe2 (CISe), CuGaSe2 (CGSe), Cu2ZnSnSe4 (CZTSe), Cu2ZnSnS4 (CZTS) and hybrid perovskites, have been calculated by DFT particularly using very-high-density k meshes. As a result, we find that the tail state formation is negligible in CdTe, CISe, CGSe and hybrid perovskite polycrystals. However, coevaporated CZTSe and CZTS layers exhibit very large Urbach energies, which are far larger than the theoretical counterparts. Based on DFT analysis results, we conclude that the quite large tail state formation observed in the CZTSe and CZTS originates from extensive cation disordering. In particular, even a slight cation substitution is found to generate unusual band fluctuation in CZT(S)Se. In contrast, CH3NH3PbI3 hybrid perovskite shows the sharpest absorption edge theoretically, which agrees with experiment.

arXiv comment24 pages, 11 figures

References in corpus (6)

• Relativistic Solar Cells
• Optical transitions in hybrid perovskite solar cells: Ellipsometry, density functional theory, and quantum efficiency analyses for CH3NH3PbI3
• Universal rules for visible-light absorption in hybrid perovskite materials
• Quantitative determination of optical and recombination losses in thin-film photovoltaic devices based on external quantum efficiency analysis
• The Urbach tail in silica glass from first principles
• Interface band gap narrowing behind open circuit voltage losses in Cu${}_2$ZnSnS${}_4$ solar cells

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• Maximum efficiencies and performance limiting factors of inorganic and hybrid perovskite solar cells
• Ab initio calculation of the detailed balance limit to the photovoltaic efficiency of single p-n junction kesterite solar cells
• Giant oscillator strength in the band-edge light absorption of zincblende, chalcopyrite and kesterite solar cell materials