3.17% efficient Cu2ZnSnS4–BiVO4 integrated tandem cell and a large scale 5 × 5 cm integrated CZTS–BiVO4 tandem device for standalone overall solar water splitting was assembled for the first time.
Surface passivation of the CdS/Cu 2 ZnSnS 4 photocathode by a HfO 2 layer was found to be very effective for enhancing the photoelectrochemical stability. The dependence of the photoelectrochemical performance, especially the stability of the Cu 2 ZnSnS 4 -based photocathode, on the thickness of the HfO 2 film was systematically investigated. The thickness of the HfO 2 layer obviously influenced the PEC stability and efficiency of the Cu 2 ZnSnS 4 -based photocathode. The CdS/Cu 2 ZnSnS 4 photocathode modified with a 6 nm thick HfO 2 layer showed long-term PEC photocurrent stability of over 10 h while still retaining high half-cell solar-to-hydrogen efficiency (HC-STH) of 2.7%. Finally, we fabricated an unbiased solar water splitting device based on the Pt/HfO 2 /CdS/Cu 2 ZnSnS 4 photocathode in tandem with a BiVO 4 photoanode, and this tandem device not only exhibited an unassisted STH conversion efficiency of 1.046% but also showed a high long-term stability of over 10 h.
A highly efficient, low-cost and environmentally friendly photocathode with long-term stability is the goal of practical solar hydrogen evolution applications. Here, we found that the Cu3BiS3 film-based photocathode meets the abovementioned requirements. The Cu3BiS3-based photocathode presents a remarkable onset potential over 0.9 VRHE with excellent photoelectrochemical current densities (~7 mA/cm2 under 0 VRHE) and appreciable 10-hour long-term stability in neutral water solutions. This high onset potential of the Cu3BiS3-based photocathode directly results in a good unbiased operating photocurrent of ~1.6 mA/cm2 assisted by the BiVO4 photoanode. A tandem device of Cu3BiS3-BiVO4 with an unbiased solar-to-hydrogen conversion efficiency of 2.04% is presented. This tandem device also presents high stability over 20 hours. Ultimately, a 5 × 5 cm2 large Cu3BiS3-BiVO4 tandem device module is fabricated for standalone overall solar water splitting with a long-term stability of 60 hours.
Compound semiconductor GeSe nanosheet-based thin films were systematically researched for application in solar water splitting. p-type GeSe films obtained from the rapid thermal sublimation method have a sheetlike grain structure and a homogeneous elemental distribution, which is suitable for application in photocathodes for solar hydrogen production. Deposition of a CdS layer on top of GeSe was found to be effective in enhancing the photoelectrochemical properties due to the p−n junction formed at the interface of CdS/GeSe that enhances the separation rate of photoexcited carriers. Furthermore, the atomic layer deposition of the TiO 2 overlayer under the CdS/GeSe photocathode not only protects the CdS from photocorrosion but also reduces surface recombination, which could generally enhance photocathode performance. The obtained Pt-TiO 2 /CdS/GeSe photocathode generated ∼10.5 mA/cm 2 under 0 V RHE and presented an onset potential of ∼0.45 V RHE . The calculated half-cell solar-to-hydrogen (HC-STH) efficiency of the obtained Pt-TiO 2 /CdS/GeSe photocathode was over 1%, and the stacked photocathode exhibited an appreciable photoelectrochemical stability of more than 8 h. It was found that the relationship between H 2 evolution amount and illumination time is almost linear, with more than 105 μmol of H 2 accompanied by ∼54 μmol of O 2 evolving throughout the detection period of 3 h under sustained solar light illumination.
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