CsCl Seed Layer Engineering for Buried-Interface Modification Enabling >20% Efficiency in Single-Source Vapor-Deposited Perovskite Solar Cells

Abstract

The single-source vapor deposition (SSVD) technique offers a simple, low-cost route with great potential for large-scale fabrication of perovskite films.However, it often yields with inhibited nucleation, leading to interfacial voids, pinholes, and inhomogeneous grain growth. To address this, a CsCl seed layer with island-like growth characteristics was introduced into the substrate prior to the SSVD of FAPbI 3 powders to improve film formation. This layer serves as an interfacial buffer, providing abundant nucleation sites and reducing buried interfacial defect density. This Seed Layer Engineering enables controlled nucleation and uniform crystal growth, resulting in dense, homogeneous perovskite films with suppressed nonradiative recombination.Consequently, the photovoltaic performance of the devices is significantly improved, achieving a power conversion efficiency (PCE) of 20.26%, compared to 17.82% for the control. Moreover, the unencapsulated devices retain 85.3% of their initial efficiency after 1000 h of aging under 40%-50% relative humidity at ∼25 °C. This work provides an effective and scalable interfacial engineering strategy to enhance the performance and stability of single-source vapor deposited perovskite solar cells, paving to the way for high-efficiency, large-area perovskite optoelectronics.