Fullerene modification of WO₃ electron transport layer toward high-efficiency MA-free perovskite solar cells with eliminated light-soaking effect

In perovskite solar cells (PSCs), the light-soaking effect, which means device performance changes obviously under continuous light illumination, is potentially harmful to loaded devices as well as accurately assessing their efficiency. Herein, chemically stable tungsten trioxide (WO3) with high electron mobility is used as electron transport material in methylamine (MA)-free PSCs. However, the light-soaking effect is observed apparently in our devices. A fullerene derivative, C-60 pyrrolidine Tris-acid (CPTA), is introduced to modify the interface between WO3 and perovskite (PVK) layers, which can bond with WO3 and PVK simultaneously, leading to the passivation of the defect and the suppression of trap-assisted nonradiative recombination. What is more, the introduction of CPTA can enhance the built-in electric field between WO3 and PVK layers, thereby facilitating the electron extraction and inhibiting the carrier accumulation at the interface. Consequently, the light-soaking effect of WO3-based PSCs has been eliminated, and the power conversion efficiency has been boosted from 17.4% for control device to 20.5% for WO3/CPTA-based PSC with enhanced stability. This study gives guidance for the design of interfacial molecules to eliminate the light-soaking effect.