Harmonizing the bilateral bond strength of the interfacial molecule in perovskite solar cells

Interfacial molecules have been demonstrated to improve the photovoltaic performance of perovskite solar cells (PSCs). However, the effect is influenced by the targeted substrate and, in particular, by its bond with the interfacial molecule. A weaker bonding of the interfacial molecule with the substrate usually implies a stronger bonding with the perovskite that could lead to uncontrollable insertion of the interfacial molecule into the perovskite bulk, resulting in device degradation. Here we select bis(2-aminoethyl) ether (BAE) as the interfacial molecule between the perovskite and the electron transport layer (ETL) in n–i–p PSCs and develop a strategy to harmonize the strength of the bilateral bonds of BAE. In particular, we manipulate the electronic structure of the ETL with doping to increase the strength of the BAE–ETL bond. This thereby results in a weakening of the BAE–perovskite bond. The harmonization in bilateral bonds of the interfacial molecule leads to PSCs with an efficiency surpassing 26.5% (certified as 26.31%) and improved stability. The interfaces in perovskite solar cells are critical to the device performance. Li et al. tune the bond strength of the interfacial molecule with the perovskite and the electron transport layer, increasing the power conversion efficiency of the cells.