GaP/GaNP Heterojunctions for Efficient Solar‐Driven Water Oxidation

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2017-06, Vol.13 (21), p.n/a
• Main Authors: Kargar, Alireza, Sukrittanon, Supanee, Zhou, Chang, Ro, Yun Goo, Pan, Xiaoqing, Dayeh, Shadi A., Tu, Charles W., Jin, Sungho
• Format: Article
• Language: English
• Subjects: Absorption spectra; alkaline electrolytes; Bias; Chemical synthesis; Coating; Current efficiency; Electrode potentials; GaNP; GaP; Heterojunctions; Hydrogen; Molecular beam epitaxy; Nanotechnology; Oxidation; Photoelectric effect; Photoelectric emission; solar‐driven water oxidation; thin film heterojunctions; Thin films; Titanium oxides; Water splitting
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201603574

The growth and characterization of an n‐GaP/i‐GaNP/p+‐GaP thin film heterojunction synthesized using a gas‐source molecular beam epitaxy (MBE) method, and its application for efficient solar‐driven water oxidation is reported. The TiO2/Ni passivated n‐GaP/i‐GaNP/p+‐GaP thin film heterojunction provides much higher photoanodic performance in 1 m KOH solution than the TiO2/Ni‐coated n‐GaP substrate, leading to much lower onset potential and much higher photocurrent. There is a significant photoanodic potential shift of 764 mV at a photocurrent of 0.34 mA cm−2, leading to an onset potential of ≈0.4 V versus reversible hydrogen electrode (RHE) at 0.34 mA cm−2 for the heterojunction. The photocurrent at the water oxidation potential (1.23 V vs RHE) is 1.46 and 7.26 mA cm−2 for the coated n‐GaP and n‐GaP/i‐GaNP/p+‐GaP photoanodes, respectively. The passivated heterojunction offers a maximum applied bias photon‐to‐current efficiency (ABPE) of 1.9% while the ABPE of the coated n‐GaP sample is almost zero. Furthermore, the coated n‐GaP/i‐GaNP/p+‐GaP heterojunction photoanode provides a broad absorption spectrum up to ≈620 nm with incident photon‐to‐current efficiencies (IPCEs) of over 40% from ≈400 to ≈560 nm. The high low‐bias performance and broad absorption of the wide‐bandgap GaP/GaNP heterojunctions render them as a promising photoanode material for tandem photoelectrochemical (PEC) cells to carry out overall solar water splitting. An n‐GaP/i‐GaNP/p+‐GaP thin film heterojunction is synthesized for efficient solar‐driven water oxidation. The TiO2/Ni‐coated n‐GaP/i‐GaNP/p+‐GaP photoanode provides high performance in 1 m KOH solution with an onset potential of ≈0.4 V versus reversible hydrogen electrode (RHE), a photocurrent of 7.26 mA cm−2 at 1.23 V versus RHE, and a broad absorption spectrum up to ≈620 nm.