Researchers from China have developed a groundbreaking method that achieves the highest solar-to-hydrogen conversion efficiency using copper zinc tin sulfide (CZTS) materials. By employing a precursor seed layer engineering (PSLE) technique, they enhanced the optical and electronic properties of CZTS photocathodes, pushing the efficiency to a record 9.91%. This innovation significantly reduces costs and presents a renewable solution for hydrogen production, highlighting the importance of cleaner energy alternatives in the face of climate change.
The finely tuned PSLE strategy led to synthesizing a high-quality CZTS. Researchers explored a versatile CZTS precursor seed layer engineering (PSLE) technique to enhance the material’s performance. They found that the PSLE shatters the performance ceiling of earth-abundant Cu2ZnSnS4 (CZTS) photocathodes, delivering a record half-cell solar-to-hydrogen (HC-STH) efficiency of 9.91%. It also enables the first unbiased CZTS-BiVO4 tandem cell to achieve 2.20% STH in natural seawater. While conventional CZTS devices stall below 8% solar-to-hydrogen efficiency due to bulk Cu_Zn antisites and interface traps affecting carrier dynamics, the use of PSLE has resulted in a significant performance enhancement.
Researchers applied precursor seed layer engineering to prepare Cu2ZnSnS4 (CZTS) light-absorbing films using a solution-processed spin-coating method. They highlighted that this method significantly improves crystal growth and mitigates detrimental defects in the post-sulfurized CZTS light-absorbing films. The effective optimization of defects enhances charge carrier dynamics and results in a highly efficient CZTS/CdS/TiO2/Pt thin-film photocathode. “PSLE-controlled nucleation creates dense, vertically aligned grains, slashes defect density to 9.88 × 10^15 cm^-3, lengthens minority-carrier lifetime to 4.40 ns, and drives photocurrent to an unprecedented 29.44 mA cm^-2 at 0 V vs RHE—within 3% of the theoretical 30.49 mA cm^-2 limit,” said researchers from Shenzhen University.
The new method aims to reduce dependence on fossil fuels, which are non-renewable and environmentally harmful. With future energy shortages anticipated, hydrogen energy presents a clean, sustainable energy source. As governments strive for net-zero goals, most current hydrogen production methods remain energy-intensive and contribute to carbon emissions, underscoring the urgent need for cleaner approaches like solar-to-hydrogen conversion through photoelectrochemical (PEC) water splitting.
Published in Nano-Micro Letters, the study reveals that the finely tuned PSLE strategy led to the synthesis of high-quality CZTS characterized by large, compact, uniform, and vertically aligned grains. Researchers fabricated and examined planar-type photocathodes consisting of Mo/CZTS/CdS/TiO2/Pt. The optimized CZTS films showed reduced passivation of bulk and interfacial defects, resulting in a superior CZTS/CdS heterojunction characterized by a higher built-in voltage (0.66 V) and lower defect density (9.88 × 10^15 cm^-3) at the interface.
Leveraging only earth-abundant materials like Cu, Zn, Sn, and S, the PSLE-enabled CZTS photocathodes cut material costs by over 70% compared to In/Ga-based chalcogenides. The method requires no rare co-catalysts and is compatible with roll-to-roll coating, thereby paving the way for a scalable solution for low-cost green hydrogen production directly from seawater. This positions CZTS as a crucial component for sustainable solar fuels and a circular hydrogen economy.