Charged States and Band-Gap Narrowing in Codoped ZnO Nanowires for Enhanced Photoelectrochemical Responses

TL;DR

This study uses first-principles calculations to show how codoping ZnO nanowires with N, P, and Ga can narrow the band gap and enhance photoelectrochemical responses, aiding water splitting applications.

Contribution

It proposes a codoping strategy to further red-shift optical absorption and improve photocurrent in ZnO nanowires, supported by theoretical calculations and experimental consistency.

Findings

Negatively charged nitrogen defects narrow the band gap.

Codoping with N, P, and Ga enhances visible light absorption.

The strategy improves photocurrent for water splitting applications.

Abstract

By means of first-principles calculations within the density functional theory, we study the structural and optical properties of codoped ZnO nanowires and compare them with those of the bulk and film. It is disclosed that the low negatively charged ground states of nitrogen related defects play a key role in the optical absorption spectrum tail that narrows the band-gap and enhances the photoelectrochemical response significantly. A strategy of uncompensated N, P and Ga codoping in ZnO nanowires is proposed to produce a red-shift of the optical absorption spectra further than the exclusive N doping and to get a proper formation energy with a high defect concentration and a suppressed recombination rate. In this way, the absorption of the visible light can be improved and the photocurrent can be raised. These observations are consistent with the existing experiments, which will be helpful to improve the photoelectrochemical responses for the wide-band-gap semiconductors especially in water splitting applications.