Controlling Doping and Defect Activity Towards Photostable Tin-Halide Perovskites
Filippo De Angelis a
a Department of Chemistry, Biology and Biotechnology and INSTM, University of Perugia, Via Elce di Sotto 8, I-06123, Perugia, Italy
Invited Speaker Session, Filippo De Angelis, presentation 158
Publication date: 6th February 2024

Replacing lead by less toxic elements remains a major challenge for the widespread uptake of perovskite-based technologies. Tin appears the only candidate to replace lead, due to the accidentally similar structural and electronic properties of these two elements. A major difference, however, is the stability of Sn(IV) phases, which are related to the lower oxidation potential of tin compared to lead. A related phenomenon is the stability of tin vacancies, which introduce significant p-doping in tin-halide perovskites (THPs), while their lead-based counterpart are essentially intrinsic semiconductors. Defect activity clearly controls doping and could also contribute to the instability towards Sn(IV) phases. Controlling doping and defect activity thus represents a pathway towards obtaining stable THPs with optimal optoelectronic properties. The different defect activity of tin- and lead-based materials is at the origin of their respective thermal and phot-induced degradation phenomena, including halide demixing and loss of I2 in lead-halide perovskites. 

Here we present results of advanced modelling studies on the defect mediated degradation pathways of prototypical THPs. We show how Sn-vacancies are central in promoting both material p-doping and formation of Sn(IV) phases. Interestingly, while p-doping dominates in the bulk, Sn oxidation is only favoured at surfaces or grain boundaries. Thus achieving uniform thin films coupled with proper surface passivation strategies represent a pathway towards achieving more stable THP-based devices. Surprisingly, THPs have also received a large attention because of their superior stability in water environment compared to their lead counterparts. We further unveil the key factors determining the stability of mixed-halide THPs against photoinduced halide segregation phenomena. Molecular and ionic strategies to mitigate p-doping in THPs are also presented.

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