Design and mechanism investigation of aggregation-controlled double-layer SnO2 for enhanced performance in perovskite solar cells

Abstract

Employing double-layer SnO₂ is an effective strategy for enhancing the performance of perovskite solar cells (PSCs). This study demonstrates that the annealing temperature of the second SnO₂ layer in the double-layer architecture significantly influences PSC performance. Annealing at 120 °C most effectively increases surface roughness of SnO₂ due to enhanced nanoparticle aggregation, which in turn improves electron extraction by enlarging the SnO₂/perovskite interfacial area, leading to higher device efficiency. However, two key challenges, such as poor SnO₂ nanoparticle connectivity and the presence of residual water within the SnO₂ layer annealed at 120 °C, were identified. To address these issues, a two-step annealing process was introduced for the second SnO₂ layer in the double-layer architecture—initial annealing at the optimized temperature of 120 °C, followed by an additional annealing at 150 °C. PSCs incorporating this additionally annealed double-layer SnO₂ with improved nanoparticle connectivity and reduced residual water content exhibited enhanced power conversion efficiency, increasing from 23.0% to 24.8%, and superior operational durability, with efficiency retention improving from 89% to 98% after 300 hours of continuous illumination at 25 °C. These findings provide new insights into SnO₂ nanoparticle aggregation within electron transport layers and present a practical approach for simultaneously improving both efficiency and durability in PSCs.