Key Takeaways & Executive Findings
- •• A novel precursor seed layer engineering technique significantly enhances crystal growth and mitigates detrimental defects in CZTS light-absorbing films. • The Mo/CZTS/CdS/TiO2/Pt photocathode achieves a record half-cell solar-to-hydrogen (HC-STH) efficiency of 9.91% and a photocurrent density of 29.44 mA cm−2 at 0 VRHE. • In natural seawater, the photocathode demonstrates a remarkable photocurrent density of 16.54 mA cm−2 and an HC-STH efficiency of 2.56%, with an unbiased STH efficiency of 2.20% in a CZTS-BiVO4 tandem cell. • Successful fabrication of a 4×4 cm2 module underscores the scalability and practical potential for unbiased in situ solar seawater splitting.
Abstract
Despite being an excellent candidate for a photocathode, Cu2ZnSnS4 (CZTS) performance is limited by suboptimal bulk and interfacial charge carrier dynamics. In this work, we introduce a facile and versatile CZTS precursor seed layer engineering technique, which significantly enhances crystal growth and mitigates detrimental defects in the post-sulfurized CZTS light-absorbing films. This effective optimization of defects and charge carrier dynamics results in a highly efficient CZTS/CdS/TiO2/Pt thin-film photocathode, achieving a record half-cell solar-to-hydrogen (HC-STH) conversion efficiency of 9.91%. Additionally, the photocathode exhibits a highest photocurrent density (Jph) of 29.44 mA cm−2 (at 0 VRHE) and favorable onset potential (Von) of 0.73 VRHE. Furthermore, our CTZS photocathode demonstrates a remarkable Jph of 16.54 mA cm−2 and HC-STH efficiency of 2.56% in natural seawater, followed by an impressive unbiased STH efficiency of 2.20% in a CZTS-BiVO4 tandem cell. The scalability of this approach is underscored by the successful fabrication of a 4×4 cm2 module, highlighting its significant potential for practical, unbiased in situ solar seawater splitting applications.
1. Introduction
In the modern world, fossil fuels, which are non-renewable and bad for the environment, are still the most widely used energy source that is required to be replaced to improve the standard of living on our planet. Therefore, future energy shortages are expected to be eased by hydrogen energy, a new environmentally friendly green energy source. Most of the current methods for producing hydrogen use a significant amount of electricity and cause CO2 emissions, highlighting the need for cleaner approaches such as solar-to-hydrogen (STH) conversion via photoelectrochemical (PEC) water splitting [1]. It has been widely believed that PEC water splitting using sunlight irradiation is a clean way to produce hydrogen energy.
Building upon the pioneering work of Honda and Fujishima [2], researchers have explored a wide range of semiconductor materials as a photoelectrode, to enhance their STH conversion efficiency, photocurrent density (Jph), onset potential (Von), and stability [3, 4]. The semiconductor absorber layer and absorber/buffer layer’s heterojunction form the core of PEC water splitting devices (photocathodes), where crucial processes such as charge production, transfer, separation, and recombination occur [5]. For example, the effectiveness of production of charge carriers in the p-type absorber layer and n-type buffer layer, as well as the subsequent transfers and collection of these carriers at the heterojunction interface, directly influences the current density and overall efficiency of the photocathode.
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Muhammad Abbas, Shuo Chen, Zhidong Li, Muhammad Ishaq, Zhuanghao Zheng, Juguang Hu, Zhenghua Su, Yanbo Li, Liming Ding, Guangxing Liang (2025). Highest Solar-to-Hydrogen Conversion Efficiency in Cu2ZnSnS4 Photocathodes and Its Directly Unbiased Solar Seawater Splitting. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01755-8
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Frequently Asked Questions
What is the record HC-STH efficiency achieved in this study?
The record half-cell solar-to-hydrogen (HC-STH) conversion efficiency achieved is 9.91%.
What is the photocurrent density of the CZTS photocathode at 0 VRHE?
The photocurrent density (Jph) is 29.44 mA cm−2 at 0 VRHE in 0.5 M H2SO4 electrolyte.
How does the photocathode perform in natural seawater?
In natural seawater, the photocathode exhibits a Jph of 16.54 mA cm−2 and an HC-STH efficiency of 2.56%.
What is the unbiased STH efficiency in a tandem cell?
The unbiased STH efficiency in a CZTS-BiVO4 tandem cell is 2.20%.
What is the significance of the 4×4 cm2 module?
The successful fabrication of a 4×4 cm2 module demonstrates the scalability of the approach for practical, unbiased in situ solar seawater splitting applications.
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