Models and Measurements Quantify Photon Recycling, Charge-Carrier Diffusion, and Photon Scattering Contributions to Photoluminescence in InP Nanowire Arrays

Nanowire arrays present many unique advantages for solar-to-chemical energy conversion and are good model systems to investigate how the performance of one nanowire can influence others in an array. Spatially resolved photoluminescence is a powerful experimental characterization tool to quantify optical and electronic coupling between nanowires in an array. However, three underlying mechanisms of incident photon scattering, photon recycling, and charge-carrier diffusion dictate this coupling. In this study, we present a comprehensive analysis of light absorption and emission of a single nanowire at open circuit, and subsequent re-absorption and re-emission by a neighboring nanowire. We developed a novel correlated single nanowire micro-spectroscopy and widefield imaging methodology to spatially resolve photon communication pathways between neighboring nanowires and selectively image re-emitted and reflected photons. Unique multiphysics models have been developed to couple wave optics and semiconductor photophysics to especially isolate contributions from photon recycling and electronic transport to photon emission from neighboring nanowires. By systematically varying the morphologies of the nanowires modeled, we identify pathways to maximize photon recycling between neighboring nanowires. We conclude that the measured photoluminescence is more strongly influenced by the diffusion of charge-carriers as compared to photon recycling in materials with moderate-to-large charge-carrier mobilities (> 10 cm2 V-1 s-1), and that photon recycling dictates photoluminescence intensity only when the charge-carrier mobility is low (< 1 cm2 V-1 s-1). The experimental and simulation platforms developed herein for photon management strategies can be leveraged by the semiconductor photocatalysis community to enhance solar-to-chemical conversion efficiencies in semiconductor nanowire arrays.