Control of surface defects in ZnO nanorod arrays with thermally deposited Au nanoparticles for perovskite photovoltaics

In this work, we employ vacuum deposited Au nanoparticles (∼4 nm) to control the defect density on the surface of hydrothermally synthesized ZnO nanorod arrays (ZnO-NR), which are of interest for electron-transport layers in perovskite solar cells. Using a combination of photoluminescence spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy, we show that the Au particles reduce the presence of defects in the ZnO-NR. We discuss this in terms of trap filling due to band bending at the ZnO-NR surface. As a proof-of-concept, we apply the Audecorated ZnO-NR as electron-transport layers in mixed-cation a n d m i x e d - h a l i d e l e a d p e r o v s k i t e s o l a r c e l l s (Cs0.15FA0.85PbI2.75Br0.25). Devices prepared with the Audecorated ZnO-NR electron-transport layers demonstrate higher open-circuit voltages and fill factors compared to solar cells prepared with pristine ZnO-NR, resulting in an increase in the power-conversion efficiency from 11.7 to 13.7%. However, the operational stability of the solar cells is not improved by the Au nanoparticles, indicating that bulk properties of the perovskite may limit device lifetime.