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Abstract The sol–gel method is efficient and cost‐effective for synthesizing SnO 2 sol, wherein SnO 2 nanocrystallites (NCs) are stabilized by electric double‐layer of solvated ions tightly bound to their surface. However, this strong binding makes the removal of electric double‐layer residues from the SnO 2 electron transport layer (ETL) to be difficult at low temperatures. This hinders both the close contact and subsequent growth among adjacent SnO 2 NCs, leading to severe carriers scattering at grain boundary, adversely affecting the electrical properties of SnO 2 ETL. Herein, SnO 2 sol is synthesized via an ethanol‐based sol–gel method and aqueous ammonia (NH 3 ·H 2 O) is introduced to effectively clean stubborn electric double‐layer residues within the SnO 2 ETL at a low temperature (80 °C). Removing residues reduces the gap among adjacent SnO 2 NCs and promotes further reconstructed growth through oriented attachment (OA), thereby reducing the number of grain boundaries. Hence, the energy barriers for electron transport decrease within the SnO 2 ETL. Furthermore, MHP prepared on the treated ETL has fine‐tuned energy level alignment, improving the electron extraction capacity. Consequently, flexible perovskite solar cells (f‐PSCs) incorporating this ETL achieved a notable increase in power conversion efficiency, rising from 19.16% to 23.71%, as well as superior mechanical stability.
Zhang et al. (Wed,) studied this question.