Low-Temperature Removal of Residual Dimethylammonium via Surface Molecular Oligomerization for CsPbI₃ Perovskite Solar Cells

Inorganic CsPbI3 perovskite shows great potential in the field of photovoltaics due to its chemical and thermal stability. High-temperature (>320 °C) annealing is required to achieve the photoactive perovskite phase of CsPbI3, which, however, is not compatible with applications on thermally vulnerable substrates, such as silicon wafers and organics. Although approaches adopting HI effectively reduce the formation temperature of perovskite-phase CsPbI3, dimethylamine hydroiodide (DMAI) is inevitably formed as a thermally resilient byproduct that is hard to remove, which causes film heterogeneity, interfacial energy mismatch, and a negatively impacted device performance. Here, we develop a low-temperature strategy for the removal of DMAI to give efficient CsPbI3 perovskite solar cells (PSCs). We demonstrate that 2-thiophenylboric acid molecules will undergo a condensation reaction at a low post-annealing temperature (∼100 °C). During this process, the generation of H2O molecules is conducive to the removal of residual DMAI and the reconstruction of the film surface morphology. Meanwhile, the remaining boro-thiophene trimer moiety could reduce Pb0 defects by forming coordinative bonds therein, while effectively suppressing carrier recombination and optimizing interfacial energy alignment for efficient carrier transport. This work envisions a promising potential to fabricate high-performance CsPbI3 PSCs.