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 SnO 2 ETL. The defects in the SnO 2 ETL are effectively suppressed by passivating the oxygen vacancies upon the SnO 2 surface. Simultaneously, the carrier mobility and crystallinity of SnO 2 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 SnO 2 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 SnO 2 /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 SnO 2 and perovskite layers after AMPA modification.