Improved Performance and Moisture Stability of Interface-Engineered Perovskite Solar Cells with the TOP-3 Hole-Transporting Material

Perovskite solar cells (PSCs) based on formamidinium (FA) and cesium (Cs) have shown improved thermal stability; however, their stability under humid conditions remains a significant challenge. In this study, a two-step protection of perovskite device via utilizing tetraoctylammonium bromide (TOAB) as a surface treatment agent and TOP-3 as a hole-transporting layer has been employed to resist unfavorable device degradation agents. TOAB serves as a multifunctional agent by passivating trap states, imparting hydrophobicity, reducing energy mismatch between perovskite and TOP-3 hole-transporting layer (HTL), and facilitating efficient hole extraction through interaction with HTL. The PCE of ambient air-fabricated PSCs enhanced from 17.09% to 19.80% for TOAB-modified devices, with a significant increase in V OC from 1.09 to 1.13 V. Moreover, the unencapsulated TOAB-coated device showed enhanced stability above 90% of the initial PCE until 480 h, above 80% after 980 h, and 67% of its initial PCE after 1200 h under ambient air with 70% relative humidity (RH). In contrast, the performance of the control device declined abruptly within a few hours of storage and retained less than 29% of the initial value under the same conditions after 1200 h. Also, excellent shelf life was found for the TOAB-coated device, retaining above 80% of its initial PCE after 300 days and about 74% after 400 days under dark storage in air under 30% RH conditions. These results highlight TOAB as a promising material for achieving highly efficient and moisture-stable PSCs.