Boosting Wavelength-Selective Absorption and Photocarrier Collection in NiO/ZnO Transparent Photovoltaic Heterojunctions by Plasmonic Ag Nanowire Top Electrodes

Global climate change has compelled many to rely on photovoltaic (PV) technology to meet the highly demanding energy needs of urban areas. In particular, transparent photovoltaic (TPV) devices can be utilized for building windows, not only supplying electric energy but also improving the overall thermal efficiency of a building. In this work, NiO/ZnO wide-bandgap oxide TPV heterojunctions are fabricated with Ag nanowire (NW) top electrodes and their PV characteristics are investigated. Special attention is paid to the contributions of surface plasmon (SP) excitation in AgNWs to the PV performance of the TPV device. Light polarized perpendicular to the AgNW axis induces a localized SP resonance in AgNWs at a wavelength of 400 nm, as shown by optical measurements and calculations. The investigation on how the plasmonic AgNWs affect real-space electric potential distributions and local current-voltage characteristics of the TPV devices uses Kelvin probe force microscopy and current-sensing atomic force microscopy, respectively. The spatial redistribution and transport of photogenerated charge carriers strongly depend on the polarization as well as the wavelength of incident light. The results demonstrate that the AgNW-based top electrodes boost the wavelength-selective absorption and the effective collection of photocarriers in TPV devices.