ConspectusTin-halide perovskites (THPs) have emerged as an attractive low band-gap (≈1.3 eV) alternative to lead-halide perovskites (LHPs) in solar cell devices. Despite the large effort, the efficiency and stability of THPs are still sensibly lower than LHPs, mainly due to the elevated p-doping and the easy oxidation of Sn(II) to Sn(IV). In this Account, we review the theoretical advancements in the understanding of the key factors originating THP limitations and the strategies to be adopted to increase efficiency and stability. In the first part, the fundamental electronic properties of THPs are discussed by focusing on the role of the metal in modulating band alignment and electron−phonon interaction. Hence, the discussion moves to the analysis of the defect chemistry of THPs and the origin of the p-doping. This is originated by the high stability of acceptor defects (VSn2−, Ii−) which are not compensated by donor-type defects under typical growth conditions, leading to increased hole densities in the valence band. The increased p-doping, besides reducing the lifetimes of photo-generated carriers, has also a negative impact on the stability of THPs by triggering tin oxidation at the surface. Hence, we discuss practical stabilization strategies that have emerged from our computational studies. Working on composition, halide-alloying, e.g., the partial substitution of I with Br, and the doping with trivalent cations represent effective strategies to mitigate the p-doping through the stabilization of the VBM and the charge compensation of acceptor defects, without dramatically affecting the band gap of THPs. Surface passivation with 2D perovskite and n-dopant molecules, such as n-DMBI-H, is useful to preserve the long-term stability and the efficiency through the passivation of surface defects. Finally, the importance of additive engineering is outlined by discussing the mechanism of action of SnF2 and its role in controlling the p-doping through a selective removal of Sn(IV) species from the precursor solution. While significant challenges remain, we hope that these theoretical results may contribute to the development of the theoretical framework guiding experiments toward the development of stable and efficient tin perovskite solar cells
Gregori et al. (Fri,) studied this question.