Lowering Charge Transport Barriers by Eliminating the Electric Double Layer Residues to Reconstruct Adjacent SnO2 Nanocrystals for High‐Efficiency Flexible Perovskite Solar Cells

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.