Boosting\nStability of Cesium/Formamidinium Based Perovskite\nSolar Cells via Eliminating Intermediate Phase Transition and X‑Anion\nVacancy

Boosting\nthe stability of cesium/formamidinium (Cs/FA) based perovskite\nsolar cells (PSCs) has received tremendous attention. However, the\ncrystallization of perovskites usually undergoes complex intermediate\nphase transitions and ion loss processes, which seriously degrade\nthe efficiency and stability of PSCs. Herein, iodine monobromide (IBr,\nan interhalogen) is incorporated into the precursor solution to regulate\nthe perovskite crystallization process. IBr can directly induce the\nformation of perovskite crystal nuclei in the intermediate film, avoiding\na complex phase transformation (2H-4H-3C). This leads to a reduction\nin the impurity phase, an increase in grain size, and an improvement\nin crystal quality. Furthermore, IBr can effectively compensate X-anion\nvacancy, thereby reducing defect density and nonradiative recombination,\nwhich enhances device performance. Thus, the efficiency of the optimal\ndevice is 24.82%. Simultaneously, the device demonstrated excellent\nstability. After 400 h of continuous operation, the efficiency value\nof the unencapsulated PSCs still retains 89% of its initial value.\nThis study provides an effective strategy for manufacturing PSCs with\nexcellent efficiency and stability.