In-situ compensation for thermal strain by phase transformation strain in all-inorganic perovskite solar cells

Abstract

The presence of defects and residual tensile strain in perovskites has a significant and deleterious impact on the efficiency and stability of all-inorganic perovskite solar cells (PSCs). Here, dimethyl sulfoxide (DMSO) with strong polarity and high boiling point is introduced into the PbBr2 precursor to delay the crystallization of PbBr2, leading to the formation of high-quality PbBr2 films by delaying the solution reaching supersaturation. The formation of PbBr2(DMSO) adduct facilitates the complete reaction of PbBr2 with CsBr via intramolecular exchange, thus preventing the formation of impurity phases such as CsPb2Br5. As a result, the defect density of CsPbBr3 films decreased by 33% due to the improved phase purity, thicker films, larger grain sizes, and reduced grain boundaries. The small porosity of PbBr2 film combined with a more complete phase-conversion process results in an expanded perovskite film that experiences compressive strain, effectively compensating for the tensile strain generated during annealing and thereby achieving the goal of strain relaxation. The optimized DMSO-based device, which exhibits compressive strain and minimal defects, achieves a remarkable efficiency of 10.11% with an open-circuit voltage of up to 1.611 V. Additionally, the unencapsulated PSC demonstrates excellent stability under 80% relative humidity and 80 °C over 30 days.