Enhancing buried interfacial toughness and performance in n–i–p perovskite solar cells via dipolar molecular interlayers

Abstract

Due to its excellent thermal and chemical stability, tin dioxide (SnO₂) has emerged as a promising electron transport layer (ETL) for high-efficiency n–i–p perovskite solar cells (PSCs). However, for perovskite films deposited on SnO₂, the surface hydroxyl groups of SnO₂ and lattice mismatch lead to severe nonradiative charge recombination at the buried interface. Moreover, the inherent brittleness of the perovskite renders the buried interface mechanically more vulnerable. In this work, a dipolar π-conjugated molecule, 3,5-diaminobenzotrifluoride (CF3-mDA), is employed as a buffer layer to modify the buried interface of PSCs with a relatively wide bandgap (1.60 eV). This buffer layer effectively coarsens the perovskite grains at the buried interface, increasing the grain size from 381.50 nm to 503.47 nm, and further enhances the mechanical toughness of the buried interface and mitigates the risk of interfacial fracture. Furthermore, it passivates the defects of both SnO₂ and the perovskite through its functional groups, as well as induces a more favorable energy band alignment. With this buried interface modification, the champion device's average power conversion efficiency (PCE) increased from 18.74% to 21.93% (22.12% under reverse scan, RS, and 21.74% under forward scan, FS), with the average open-circuit voltage (V_OC) boosted from 1.188 V to 1.232 V and a significantly suppressed hysteresis. The modified devices also show a higher environmental stability than the control counterparts, maintaining an average of 85.20% of their initial PCE after 16 days of storage in ambient air (with 25% relative humidity, RH, and at room temperature, RT).