Multifunctional Biguanide Salts as Efficient Defect Passivators for High-Performance Inverted Perovskite Solar Cells

The high defect density in perovskite materials poses a significant challenge to improving the efficiency and long-term stability of perovskite solar cells (PSCs). To address this, molecules featuring electron-donating or electron-withdrawing groups have been utilized for defect passivation. In this study, biguanide hydrochloride (BH), a multifunctional organic molecule, was introduced into the perovskite layer. The nitrogen groups in BH establish strong chemical interactions with Pb2+ ions, altering the perovskite’s crystallization direction, significantly reducing defect state density, suppressing nonradiative recombination, enhancing carrier separation efficiency, and promoting carrier transport. PSCs incorporating BH achieved a notable power conversion efficiency (PCE) of 23.51%, with a short-circuit current density (JSC) of 24.85 mA cm–2 and an open-circuit voltage (VOC) of 1.13 V. Following 1500 h of aging under 35% relative humidity, BH-modified PSCs demonstrated exceptional environmental stability, retaining 95.1% of their initial PCE, significantly outperforming control devices. This study presents an innovative approach by exploiting the strong chelating ability of biguanide hydrochloride (BH) to expand the application of guanidine derivatives in perovskite photovoltaics. The proposed strategy not only enhances device performance (PCE) but also ensures long-term operational durability, paving the way for next-generation stable and efficient perovskite solar cells.