Alumina Nanoparticle Interfacial Buffer Layer for Low-Bandgap Lead-in Perovskite Solar Cells

Mixed lead-tin (Pb:Sn) halide perovskites are promising absorbers with narrow-bandgaps (1.25-1.4 eV) suitable for high-efficiency all-perovskite tandem solar cells. However, solution processing of optimally thick Pb:Sn perovskite films is notoriously difficult in comparison with their neat-Pb counterparts. This is partly due to the rapid crystallization of Sn-based perovskites, resulting in films that have a high degree of roughness. Rougher films are harder to coat conformally with subsequent layers using solution-based processing techniques leading to contact between the absorber and the top metal electrode in completed devices, resulting in a loss of V-OC, fill factor, efficiency, and stability. Herein, this study employs a non-continuous layer of alumina nanoparticles distributed on the surface of rough Pb:Sn perovskite films. Using this approach, the conformality of the subsequent electron-transport layer, which is only tens of nanometres in thickness is improved. The overall maximum-power-point-tracked efficiency improves by 65% and the steady-state V-OC improves by 28%. Application of the alumina nanoparticles as an interfacial buffer layer also results in highly reproducible Pb:Sn solar cell devices while simultaneously improving device stability at 65 degrees C under full spectrum simulated solar irradiance. Aged devices show a six-fold improvement in stability over pristine Pb:Sn devices, increasing their lifetime to 120 h.

Automated summary

Mixed lead-tin halide perovskites show potential for high-efficiency tandem solar cells, but solution processing of thick films is challenging due to rapid crystallization and rough surfaces. This study improves the conformality of subsequent layers using alumina nanoparticles on the surface of rough films, resulting in a 65% increase in maximum-power-point efficiency and 28% improvement in steady-state V-OC. The nanoparticles also enhance device stability, with a six-fold increase in lifetime compared to pristine films.