Research Highlights

• A scalable internal–external synergistic dual-electron extraction strategy overcomes the intrinsically low carrier-extraction efficiency of single-junction p-InGaN nanowire photocathodes.
• An internal electron-blocking layer directs photogenerated electrons toward the nanowire/electrolyte interface while facilitating rapid hole collection.
• Surface sulfurization strengthens band bending, accelerates interfacial electron transfer, and optimizes hydrogen adsorption energetics.
• The optimized photocathode delivers a photocurrent density of −3.40 mA cm⁻² at 0 V versus RHE, an onset potential of 0.82 V versus RHE, and stable hydrogen evolution for more than 300 h without a protective coating.

Introduction

In April 2026, Nano-Micro Letters published online the latest work from researchers at the University of Science and Technology of China in the field of photoelectrochemical hydrogen evolution. The team developed a scalable internal–external synergistic dual-electron extraction strategy that establishes rapid bulk–surface–electrolyte electron transport in single-junction p-InGaN nanowires, thereby markedly enhancing photoelectrochemical hydrogen-evolution performance. Xudong Yang, Yuying Liu, Wei Chen, and Tianle Zhang contributed equally as co-first authors; Haiding Sun and Jiajie Xu are the corresponding authors.

Background

Efficient, durable, and scalable photocathodes are essential for large-scale solar hydrogen production. Single-junction semiconductor photocathodes are particularly attractive because of their simple architecture, low cost, and mature fabrication processes, yet their carrier-extraction efficiency is intrinsically limited.

To address this challenge, the researchers proposed a synergistic dual-electron extraction strategy that unlocks the hydrogen-evolution potential of single-junction p-InGaN nanowires. The optimized p-InGaN photocathode achieved a photocurrent density of −3.40 mA cm⁻² at 0 V versus RHE—37.8 times that of the unmodified device—together with an onset potential of 0.82 V versus RHE and stable hydrogen production for more than 300 h without an additional protective layer.

Internally, an electron-blocking layer was incorporated into the p-InGaN nanowires to suppress electron backflow toward the substrate and promote electron transport to the nanowire/electrolyte interface. Externally, surface anion doping of the InGaN nanowires enhanced band bending, accelerated interfacial electron transfer, and optimized the hydrogen adsorption free energy. This coordinated strategy substantially improves electron utilization in a single-junction photocathode and offers a new route for overcoming the intrinsic limitations of wafer-scale III-nitride photoelectrodes.

Instrumentation Used in the Study

Perfectlight PLS-CS300 Xenon Light Source

The study used a simulated 300 W PLS-CS300 xenon lamp equipped with an AM 1.5G filter for photoelectrochemical measurements under one-sun illumination. Through optimization of the lamp housing and light-guiding architecture, the PLS-CS300 substantially increases optical output power. Tests conducted at different operating currents under otherwise identical geometric conditions show an improvement of more than 30%, supporting faster and broader photocatalytic and photoelectrochemical applications.

Figure-by-Figure Analysis

1. Internal Optimization: Constructing an Electron-Blocking Layer

As shown in Figure 1, the researchers used bottom-up plasma-assisted molecular beam epitaxy under nitrogen-rich conditions to grow highly crystalline single-junction p-InGaN nanowires epitaxially on an n-Si (111) substrate. Precise interface control during epitaxy enabled the incorporation of an electron-blocking layer (EBL) comprising n⁺⁺-GaN, InGaN, and p⁺⁺-GaN into the single-junction p-InGaN nanowires. This architecture promotes electron–hole separation and transport. Multiple electron-microscopy techniques confirmed high-quality epitaxial growth across the silicon wafer and verified the intended EBL structure.

2. Internal Optimization: Performance and Mechanistic Analysis

The InGaN/GaN/Si and InGaN/EBL/GaN/Si photocathodes were systematically evaluated in a three-electrode photoelectrochemical system. The EBL-containing device exhibited substantially enhanced hydrogen-evolution performance: at 0 V versus RHE, its photocurrent density reached −0.79 mA cm⁻², 8.8 times the −0.09 mA cm⁻² obtained with InGaN/GaN/Si.

Experiments and simulations clarified how the EBL improves internal carrier separation and transport. In the single-junction p-InGaN photocathode, p-InGaN serves both as the light absorber and as the active surface for hydrogen evolution, allowing photogenerated electrons to migrate directly to the p-InGaN/electrolyte interface. Without the EBL, however, the internal electric field formed between n-GaN and p-InGaN drives some electrons into the external circuit rather than toward the electrolyte, reducing the number available for hydrogen evolution. At the same time, photogenerated holes in p-InGaN must cross a high barrier associated with the underlying n-GaN segment before entering the circuit. Slow hole transport increases electron–hole recombination and further depletes the surface electron population.

Inserting the EBL between p-InGaN and n-GaN directs more photogenerated electrons toward the p-InGaN/electrolyte interface while enabling holes to enter the external circuit more rapidly. The EBL therefore increases the number of electrons available for surface reactions and simultaneously improves internal hole transport.

3. External Optimization: Sulfurizing the InGaN Surface

Although the internal EBL substantially increased the number of photogenerated electrons reaching the p-InGaN surface, the intrinsically inert surface continued to impede electron transfer to the electrolyte. Wurtzite InGaN offers electronically tunable surface properties that can be modified through metal or nonmetal doping. Here, a straightforward sulfurization treatment introduced sulfur anions into the InGaN surface, forming an InGaSN/InGaN surface structure and creating a more efficient electron-transfer pathway from p-InGaN to the electrolyte.

Electron microscopy confirmed the successful introduction of sulfur at the InGaN surface. Comparative X-ray photoelectron spectroscopy (XPS) and surface-sensitive soft X-ray absorption spectroscopy (sXAS) further revealed the changes in surface chemical states and electronic interactions induced by sulfurization.

4. External Optimization: Performance and Mechanistic Analysis

The influence of the electron-rich sulfurized surface on the photoelectrochemical hydrogen-evolution activity of InGaSN/InGaN/EBL/GaN/Si was evaluated in a standard three-electrode system using 0.5 M H₂SO₄ as the electrolyte. Relative to InGaN/EBL/GaN/Si, the sulfurized photocathode showed a pronounced improvement: the photocurrent density at 0 V versus RHE increased from −0.79 to −3.40 mA cm⁻², while the onset potential rose from 0.63 to 0.82 V versus RHE.

The single-junction InGaSN/InGaN/EBL/GaN/Si photocathode also operated stably for approximately 300 h without any protective layer. Overall, the internal–external synergistic strategy increased the photocurrent density of the single-junction p-InGaN photocathode from −0.09 to −3.40 mA cm⁻² at 0 V versus RHE—a 37.8-fold enhancement. Compared with a range of recently reported advanced photocathodes, the final device combined a favorable onset potential with outstanding operational durability.

Experimental characterization and density functional theory calculations elucidated the role of surface sulfurization. Steady-state and time-resolved photoluminescence measurements showed that sulfurization suppresses photogenerated electron–hole recombination and improves effective carrier separation. Because sulfur contributes one more valence electron than the nitrogen atom it replaces, it acts as an effective n-type dopant, increasing surface electron filling and shifting the Fermi level upward. When the surface InGaSN layer contacts bulk InGaN, electrons redistribute to equalize the Fermi levels, producing pronounced downward band bending in the bulk InGaN and driving photogenerated electrons toward the surface. Surface sulfurization also optimizes the hydrogen adsorption free energy, establishing a rapid electron-transfer pathway from p-InGaN to the electrolyte and thereby accelerating hydrogen-evolution kinetics.

Summary

This study presents a scalable internal–external synergistic dual-electron extraction strategy that fundamentally improves the utilization of photogenerated carriers in single-junction p-InGaN nanowires. Internally, an electron-blocking layer suppresses electron backflow toward the substrate, directs electrons to the nanowire/electrolyte interface, and enables rapid hole collection by the external circuit. Externally, anion-enabled surface sulfurization modifies the InGaN band structure, strengthens the driving force for electron transfer to the electrolyte, and optimizes hydrogen adsorption energetics to accelerate reaction kinetics.

The optimized p-InGaN photocathode achieved a photocurrent density of −3.40 mA cm⁻² at 0 V versus RHE, representing a 37.8-fold increase over the unmodified device, together with an onset potential of 0.82 V versus RHE. Notably, it sustained hydrogen evolution for more than 300 h in an acidic electrolyte without a surface-protection layer. The strategy provides a general and scalable approach to alleviating electron backflow and interfacial transport bottlenecks in single-junction III-nitride photoelectrodes.

Author Profile

Haiding Sun
Corresponding Author; Professor, University of Science and Technology of China

Haiding Sun is a professor and doctoral supervisor in the School of Microelectronics at the University of Science and Technology of China and leads the USTC iGaN Laboratory. He has received support through the National Science Fund for Excellent Young Scholars, the Anhui Provincial Science Fund for Distinguished Young Scholars, and a high-level talent program of the Chinese Academy of Sciences. His research focuses on the epitaxial growth of gallium nitride semiconductor materials and the design and fabrication of optoelectronic and photoelectrochemical devices.

Professor Sun has published more than 180 SCI-indexed papers, including over 10 ESI Highly Cited Papers, with more than 8,500 Google Scholar citations. As a corresponding author, he has published more than 100 papers in major international journals, including Nature Photonics, Nature Electronics, Nature Communications, and Science Advances, as well as four papers at the IEEE International Electron Devices Meeting. He has contributed chapters to four books and holds more than 20 granted patents.

He has served on the organizing or technical program committees of international conferences including IEDM, CLEO, and IEEE IPC. His editorial service includes an associate editorship at IEEE Photonics Technology Letters and early-career editorial-board roles at Journal of Semiconductors, Nano-Micro Letters, and Materials Today Electronics. He has led projects funded through national key research programs and the National Natural Science Foundation of China, was recognized as an Outstanding Supervisor of the Chinese Academy of Sciences for three consecutive years, appeared in the World’s Top 2% Scientists list from 2021 to 2025, and was named an Elsevier Highly Cited Chinese Researcher in 2024 and 2025.

Publication Details

X. Yang, Y. Liu, W. Chen, T. Zhang, et al. “Wafer-Scaled III-Nitrides Nanowire Photocathodes Enabled by Synergistic Dual-Electron Extraction for Efficient Solar-to-Hydrogen Conversion.” Nano-Micro Letters 18 (2026) 337. https://doi.org/10.1007/s40820-026-02186-9