Enhanced light harvesting in lead-free Cs2AgBiBr6 double perovskite solar cells with plasmonic Ag nanoparticles

Lead-free Cs2AgBiBr6 double perovskite solar cells (PSCs) possess unique environment-friendly and stable attributes. However, the wide bandgap of Cs2AgBiBr6 weakens the light capture capability, thus limiting the improvement in power conversion efficiency (PCE) for PSCs. Herein, a convenient and efficient method is presented by incorporating plasmonic Ag nanoparticles (NPs) onto a perovskite surface. Owing to the synergistic effect of far-field light scattering and near-field enhancement of Ag NPs, the short-circuit current density of the modified PSC is enhanced by approximately 30%. In addition, the introduction of Ag NPs endows a larger Fermi energy level difference between the TiO2/perovskite interface, resulting in a higher open-circuit voltage. The optimized device with the structure of fluorine-doped tin oxide/compact TiO2/mesoporous TiO2/Cs2AgBiBr6/carbon delivers a PCE of 2.69% as compared to the control device with a PCE of 2.04%, which represents one of the highest efficiencies of hole transport layer-free, carbon-based PSCs. Furthermore, the unencapsulated device retains nearly 98% of its initial PCE even after being stored for 32 days at 25 °C and relative humidity of 40 ± 5%. This work provides a new insight into constructing high-efficient and environment-friendly PSCs.