Layered Halide Double Perovskites Cs_3+nM(II)_nSb₂X_9+3n (M = Sn, Ge) for Photovoltaic Applications

Over the past few years, the development of lead-free and stable perovskite absorbers with excellent performance has attracted extensive attention. Much effort has been devoted to screening and synthesizing this type of solar cell absorbers. Here, we present a general design strategy for designing the layered halide double perovskites Cs_3+nM(II)_nSb₂X_9+3n (M = Sn, Ge) with desired photovoltaic-relevant properties by inserting [MX₆] octahedral layers, based on the principles of increased electronic dimensionality. Compared to Cs₃Sb₂I₉, more suitable band gaps, smaller carrier effective masses, larger dielectric constants, lower exciton binding energies, and higher optical absorption can be achieved by inserting variable [SnI₆] or [GeI₆] octahedral layers into the [Sb₂I₉] bilayers. Moreover, our results show that adjusting the thickness of inserted octahedral layers is an effective approach to tune the band gaps and carrier effective masses in a large range. Our work provides useful guidance for designing the promising layered antimony halide double perovskite absorbers for photovoltaic applications.