Mitigating lattice strain and phase segregation of mixed-halide perovskite films via dual chloride additive strategy toward highly efficient and stable perovskite solar cells

Mixed halide perovskites could be used to fabricate the high-efficient single junction perovskite solar cells (PSCs) and also be assembled into the tandem solar cells. However, those perovskites always suffered from microstrain and phase segregation issues, which tend to bring in extra non-radiative recombinations and aggravate the energy losses and degradation of PSCs. Here, we developed a dual chloride additive strategy to overcome these issues. Compared with the pristine and single additive films, the perovskite films with dual chloride additive possessed the lowest microstrain and the least defects, and thus the activation energy related to phase segregation of those films was improved from 40.21 kJ mol-1 to 59.08 kJ mol-1. Density functional theory revealed that the iodide ion migration also had been inhibited by the dual chloride additive as the energy barrier increased from 0.41 eV to 0.57 eV. PSCs with dual chloride additive showed a efficiency of 22.94%, higher than that of the pristine PSCs (20.62%) and the single additive PSCs. Moreover, the unencapsulated PSCs with dual chloride additive exhibited better working stability maintained 93% of their original efficiency after 1000 s of MPP tracking operation in ambient air, while their counterpart PSCs maintains 46%.