Novel Multi-Pyridyl-Functionalized Spirobifluorenes as Precursor Additives for Improving Efficient and Stable Perovskite Solar Cells.

Significant advancement of additive engineering has primarily focused on the improved perovskite film quality by the regulation of crystallization rates or defect passivation, thereby enabling highly efficient and stable solar cells; however, current research on the incorporation of functional additives into perovskite precursor solutions to simultaneously gain crystallization improvement and reduced defects in the perovskite film remains a significant challenge. Herein, two novel multi-pyridyl-functionalized spirobifluorene additives (designated as SBF-3-py and SBF-4-py) achieved by a facile Suzuki cross-coupling reaction are first incorporated into the perovskite precursor for producing high-quality perovskite films. SBF-3-py or SBF-4-py with spirobifluorene and multiple pyridyl groups can form multi-site interactions with perovskite components, thereby improving the perovskite film crystallization, simultaneously passivating VI and PbI defects, modulating energy level alignment, and promoting carrier mobility. Consequently, the inverted perovskite solar cells (PSCs) with SBF-3-py or SBF-4-py treatment acquire a remarkably high power conversion efficiency (PCE) of 20.65 or 20.98% with low hysteresis, distinctly surpassing the control PSC (PCE = 18.67%), along with markedly improved stability. This work pioneers a new class of small organic additives for the simultaneous realization of crystallization improvement and defect reduction of the perovskite film in highly efficient and stable devices.