Suppression of PCBM dimer formation in inverted perovskite solar cells.

Achieving a well-controlled electron-selective layer is critical for the device scalability and performance of perovskite solar cells. While phenyl-C61-butyric acid methyl ester (PCBM) is a promising electron-selective material in inverted perovskite solar cells, its dimerization under environmental stress accelerates the material degradation and complicates producing high-quality PCBM layers, thereby compromising device long-term operational stability and scale-up fabrication. Here we investigated the PCBM molecular stacking on perovskite surfaces, finding that the variability in perovskite surface termination leads to orientation and distribution heterogeneity of the PCBM layer, resulting in undesirable dimerization. To address this, we developed a molecular dopant for suppressing PCBM dimer formation, achieving a certified efficiency of 26.4% in laboratory-scale devices and 25.3% in 1 cm2 devices. Furthermore, these devices maintained 93% of their initial power conversion efficiency after 1,500 h of ageing at 85 °C following the ISOS L-2I protocol.