CsSnI3 Quantum Dots as a Multifunctional Interlayer for High‐Efficiency Bilayer Perovskite Solar Cells

In this study, zero-dimensional/three-dimensional (0D/3D) bilayer perovskite solar cells are successfully fabricated by incorporating cesium tin triiodide (CsSnI₃) QDs as interface-regulating layers. The strategic use of CsSnI₃ QDs facilitates an improved valence band alignment between the FAPbI₃ perovskite layer and the hole transport layer (HTL), thereby enhancing efficient hole transportation. As a result, a remarkable improvement in device performance, elevating the PCE from 22.99% to 25.72% compared to unmodified PSCs, can be achieved.

Abstract

Perovskite solar cells (PSCs) have garnered significant interest due to their potential for high performance at low cost. While single-junction PSCs have surpassed 26% efficiency, they are nearing their theoretical limits. Introducing dual absorber layers can broaden the spectral absorption range, enhancing performance. This study explores a zero-dimensional/three-dimensional (0D/3D) bilayer structure combining three-dimensional (3D) FAPbI₃ with zero-dimensional (0D) cesium tin triiodide (CsSnI₃) quantum dots (QDs) as an interfacial modification layer. The CsSnI₃ QDs establish a cascade energy level structure, improving charge transfer efficiency at the perovskite-hole transport layer (HTL) interface. Their narrow bandgap enhances light absorption efficiency, boosting hole extraction and short-circuit current density. Incorporating CsSnI₃ QDs into PSCs significantly improves the power conversion efficiency from 22.99% to 25.72% compared to 3D perovskite solar cells without the CsSnI₃ QD interlayer. Also, surface-passivated CsSnI₃ QDs with hydrophobic ligands provide moisture resistance and interfacial passivation, increasing stability. Using perfluorooctanoic acid (PFA) to modify CsSnI₃ QDs further enhances moisture resistance, allowing PSCs to maintain 85% of initial efficiency for over 60 days at 25% relative humidity without encapsulation, demonstrating significant stability improvements. The incorporation of CsSnI₃ QDs in PSCs notably increases power conversion efficiency.