II–IV–V₂ and III–III–V₂ Polytypes as Light Absorbers for Single Junction and Tandem Photovoltaic Devices

Recent experiments on II–IV–V₂ type nitrides and phosphides have shown that these materials are potential candidates as photovoltaic absorbers. The materials space for such light absorbers can be expanded by elemental substitution of the different species,and thanks to the small energy difference of the polymorphs, the space can be extended by tuning the atomic structure as well. Using electronic structure calculations, we explore chalcopyrite, kesterite, and wurtzite polymorphs of II–IV–V₂ and III–III–V₂ materials for light absorption especially in the visiblerange. Based on the thermodynamic stability, band gap, and charge carrier effective masses, we discuss the posssibility for the materials containing nontoxic elements to act as PV absorbers. Additionally,the systematic mapping of the materials space provides trends in thermodynamic and electronic properties which can be exploited further to tune these properties via elemental substitution and/or alloying.