Polyamino acid-mediated crystallization and crystal stabilization in perovskite for efficient and stable photovoltaic devices

Abstract Although perovskite solar cells (PSCs) demonstrate outstanding power conversion efficiency (PCE), their practical applications are still limited by stability issues caused by various problems such as poor crystal quality triggered structural instability. Herein, to address the structural instability of perovskites, we introduced a polymer additive, poly-L-lysine hydrobromide (PLL), into the perovskite precursor to promote perovskite crystal growth, thereby constructing a stable crystal structure. The results show that the introduction of PLL modulates the colloidal aggregation state in the precursor solution, provides longer time for growth of perovskite and successfully realizes the formation of large-sized perovskite films with high crystallinity. More importantly, owing to its hydrophobic long-chain structure and the widespread distribution of C=O and NH on the chain, PLL firmly locks the perovskite crystals, enhancing their structural stability while blocking the intrusion of external factors such as water molecules, significantly enhances the overall stability of the device. The results show that the PLL-based PSC has negligible hysteresis and its PCE is improved from 22.20% to 23.66%. while the PLL-modified perovskite films and devices demonstrate excellent thermal and environmental stability. These findings highlight PLL as a promising additive for optimizing perovskite crystallization, offering guidance for fabricating efficient and stable photovoltaic devices.