Improved Absorber Phase Stability, Performance, and Lifetime in Inorganic Perovskite Solar Cells with Alkyltrimethoxysilane Strain-Release Layers at the Perovskite/TiO₂ Interface

All-inorganic β-CsPbI3 has superior chemical and thermal stability compared to its hybrid counterparts, but the stability of state-of-the-art β-CsPbI3 perovskite solar cells (PSCs) under normal operating conditions (i.e., under illumination in an inert atmosphere) remains inferior to their hybrid counterparts. Here, we found that the lattice distortion in CsPbI3 near the perovskite/electron transport layer (ETL) interface can induce polymorphic transformation in encapsulated CsPbI3 films aged under illumination. To suppress this lattice distortion, we introduced alkyltrimethoxysilane strain-release layers (SRLs) at the perovskite/ETL interface. We found the SRL with the longest alkyl chain is the most effective at reducing interfacial lattice distortion, leading to enhanced charge transfer at the perovskite/ETL interface and improved phase/device stability. Its incorporation in β-CsPbI3 solar cells resulted in a power-conversion efficiency of 20.1% and an operational lifetime with an extrapolated T80 of >3000 h for encapsulated devices tested under continuous illumination under maximum power point tracking conditions.