Photovoltaic properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>A</mml:mi><mml:mi>B</mml:mi></mml:mrow><mml:msub><mml:mi mathvariant="normal">Se</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> chalcogenide perovskites (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi></mml:math> = Ca, Sr, Ba; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>B</mml:mi></mml:math> = Zr, Hf)

Abstract

Lead-free, stable photovoltaic materials with promising optoelectronic features have recently been discovered in chalcogenide perovskites. However, a thorough theoretical analysis of excitonic and polaronic properties has never been done because it would require enormous computing. Here, we elucidate the role of excitonic and polaronic effects in a sequence of chalcogenide perovskites ${AB\text{Se}}_{3}$ ($A$ = Ca, Sr, Ba; $B$ = Zr, Hf), including their needlelike ($\ensuremath{\alpha}$-phase) and distorted ($\ensuremath{\beta}$-phase) structures, along with their relative stability and optoelectronic properties by employing state-of-the-art density functional theory, density functional perturbation theory (DFPT), and many-body perturbation theory [$GW$ and Bethe-Salpeter equation (BSE)]. We find all the investigated perovskites to be dynamically as well as mechanically stable and possess direct electronic (${G}_{0}{W}_{0}$) band gap in the range of 1.02--1.97 eV. We investigate the interplay of the ionic and electronic components of the dielectric screening through the DFPT and BSE methods and find that the electronic component predominates. Interestingly, they exhibit smaller exciton binding energy (0.02--0.10 eV) than conventional halide and sulfur-based chalcogenide perovskites. The polaronic mobility for electrons (holes) is in the range of $8.26--77.59\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}$ (19.05--100.49 ${\mathrm{cm}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}$), which also found to be much higher than that of sulfur-based chalcogenide perovskites, owing to less carrier-phonon interactions in the former. All the examined properties suggest $\ensuremath{\beta}\text{\ensuremath{-}}{AB\text{Se}}_{3}$ to be promising environmentally friendly stable materials for photovoltaic applications. This has been further confirmed by estimating spectroscopic limited maximum efficiency, which is calculated as $\ensuremath{\sim}17.5$%--23% for these materials.

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