Aminomethyl Phosphonic Acid as Highly Effective Multifunctional Additive for Modification of Electron Transport Layer and Perovskite in Photovoltaic Solar Cells

The passivation of detrimental perovskite-based defects is critically acknowledged for fabricating highly effective perovskite solar cells (PSCs). The presence of a high-quality electron transport layer (ETL) is also considered a pivotal factor for effective charge extraction and transport dynamics. Herein, a simple small organic molecule, aminomethyl phosphonic acid (AMPA), is introduced as a multifunctional additive in the SnO₂ ETL. The defects in the SnO₂ ETL are effectively suppressed by passivating the oxygen vacancies upon the SnO₂ surface. Simultaneously, the carrier mobility and crystallinity of SnO₂ are enhanced, and the upward-regulated conduction band minimum (CBM) is beneficial for constructing a favorable energy level alignment with the perovskite layer. Notably, the introduced residuals on the SnO₂ surface can function as crystalline seeds for growth of large perovskite grains, which can passivate the defects in the perovskite bulk phase, boundaries, as well as the SnO₂/perovskite interface. Consequently, the power conversion efficiency (PCE) value of the AMPA-modified PSCs is enhanced from 19.91% to 24.22%. Most importantly, the unencapsulated PSCs with AMPA maintained 94.9% of the initial PCE during 720 h of storage at a relative humidity of 10%, attributed to the improved hydrophobicity of both the SnO₂ and perovskite layers after AMPA modification.