Revealing the Critical Role of Electron‐Withdrawing Cores in Bulk Passivation of Diammonium Ligands Toward High‐Performance Perovskite Solar Cells

Abstract Diammonium derivatives with electron‐withdrawing cores of cyclohexyl or phenyl have demonstrated enormous potential in achieving high‐performance perovskite solar cells. Nevertheless, the critical role of these electron‐withdrawing cores of the diammonium passivation on device performance is yet to be elucidated. Herein, two kinds of diammonium ligands of 1, 4‐cyclohexyldimethylammonium diiodide (CyDMADI) and 1, 4‐phenyldimethylammonium diiodide (PhDMADI) are introduced into the perovskite precursor for bulk passivation. The PhDMADI system exhibits a stronger electron‐withdrawing unit of phenyl in comparison to the CyDMADI system with a cyclohexyl core, thus resulting in enhanced electrostatic interaction between uncoordinated Pb 2+ and phenyl groups and stronger hydrogen bonds between PhDMADI and the I─Pb skeleton. Such strengthened interactions between PhDMADI and perovskite effectively inhibit the generation of trap states and therefore significantly decrease non‐radiative recombination. The PhDMADI‐passivated film demonstrates mitigated microstrain and decreased grain boundary grooves （GBGs） compared with the CyDMADI‐based counterpart. Simultaneously, the PhDMADI treatment can efficiently slow down the hot‐carriers cooling dynamics process, benefiting the transfer of hot‐carriers. Consequently, the PhDMADI‐passivated device achieves an impressive efficiency of 26.04%, along with excellent operating stability which retains 90% of its initial efficiency after 1100 h tracking at the maximum power point under continuous one sun illumination.