Enhanced charge separation by oriented growth of Ta3N5-Cu2O n-p array heterojunction

Abstract

Tantalum nitride (Ta3N5) is one of the most promising photoresponsive semiconductor materials for efficient solar energy conversion, but its fast carrier recombination has hindered research progress severely. Fabricating a heterojunction structure is an effective strategy to promote the charge separation efficiency and thus enhance solar conversion efficiency. Herein, we designed a p-n heterojunction photoanode consisting of n-type Ta3N5 nanorod arrays (NRAs) that grew along the a-axis (light electron effective mass) and p-type Cu2O nanoparticles. This NRA heterojunction shortens the hole diffusion distance, transfers electrons along the a-axis effectively, and enlarges the space charge region. The heterojunction improves the charge separation efficiency of Ta3N5 NRAs significantly, and Ta3N5-Cu2O exhibits a photocurrent density of 9.19 mA cm-2 at 1.6 V vs normal hydrogen electrode (VNHE, pH = 0), an onset potential of 0.326 VNHE, and a maximum incident photon to current efficiency of 60% at 380 nm. Our results demonstrated a potential crystal oriented growth strategy of nanostructured heterojunctions for overcoming the short carrier diffusion distance and fast carrier recombination.