Multifunctional molecular linker on buried interface for efficient and stable cesium–formamidinium perovskite solar cells

Interface engineering is one of the key issues in fabricating efficient and stable perovskite solar cells (PSCs). Herein, we introduced self-assembled molecules of 3,4,5-trimethoxyphenylacetic acid (PAA) and 3,4,5-trimethoxyphenylpropionic acid (PPA) as a multifunctional linker to modify the buried interface between SnO2 and the Cs/FA perovskite. These modifiers can simultaneously bond to the SnO2 surface and chemically interact with perovskite to passivate the surface defects. Moreover, the PAA/PPA can facilitate the crystal growth of perovskite to form high-quality films. Accordingly, the defect density and trap-assisted charge recombination at the interface and within the perovskite are markedly reduced. Additionally, the large dipole moments of modifiers induce the modulation of energy level of SnO2, resulting in the favorable band alignment and thus the enhanced electron extraction and transport. As a result, PPA is certified to be more effective in interfacial regulation, and the Cs/FA-based PSC produces a significantly increased PCE of 22.2% with inhibited hysteresis, higher than the control (20.0%) and PAA-modified (21.5%) ones. Meanwhile, the unencapsulated devices with PAA/PPA modification presented much better ambient and thermal stability than the control device.