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 Pb²⁺ 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.