Influence of Cl Incorporation in Perovskite Precursor on the Crystal Growth and Storage Stability of Perovskite Solar Cells

Solar cells based on organic–inorganic hybrid lead-halide perovskites are very promising because of their high performance and solution process feasibility. Elemental engineering on perovskite composition is a facile path to obtain high-quality crystals for efficient and stable solar cells. It was found that partially substituting I– with Cl– in the perovskite precursor promoted crystal growth, with the grain size larger than the layer thickness, and facilitated the generation of a self-passivation layer of PbI2. Whereas the residual Cl– ions were suspected to diffuse to the hole-transport layer consisting of ubiquitously spiro-OMeTAD, the formation of highly bounded ionic pairing of Cl– with the oxidized state of spiro-OMeTAD led to insufficient charge extraction and severely reversible performance degradation. This issue was effectively alleviated upon Br– doping owing to the generation of Pb–Br bonds in the lattice that strengthened the phase stability by improving the binding energy between each unit. The binary halide (Br–/Cl–)-doped perovskites resulted in a champion power conversion efficiency of 20.2% with improved long-term storage stability