462505 Heterostructured c-Si/BiVO4 Core-Shell Tandem Photoanode for Unassisted Photoelectrochemical Water Splitting
A tandem-junction PEC device offers a high theoretical solar-to-hydrogen (STH) efficiency due to the additive voltages across two photoabsorbers and the better utilization of the solar spectrum. Modeling STH efficiency as a function of band gap for a tandem device shows that over 20% STH can be achieved with band gaps of 1.2 and 1.8 eV.1 One promising photoabsorber material combination is c-Si paired with a metal oxide, especially BiVO4. In addition to the appropriate band structure alignment of both semiconductors, c-Si and BiVO4 are low cost, earth abundant, and industrially scalable. However, the key challenges for these materials are the instability of c-Si in aqueous environment and the poor electronic properties of BiVO4.
In this work, we present the fabrication of a heterostructured c-Si/BiVO4 core-shell tandem based device capable of performing spontaneous water splitting without any precious metal. The wafer scaled device architecture was prepared by (1) nanostructuring of the c-Si substrate to serve as both a bottom absorber and a scaffold to improve the charge separation of BiVO4; (2) tuning the c-Si p-n junction depth to maximize the device photovoltage; (3) engineering the SnO2 interfacial layer to passivate the c-Si/BiVO4 interface and protect the c-Si p-n junction; (4) conformally coating a BiVO4 thin film on the nanostructured Si; and (5) decorating the c-Si and BiVO4 surfaces with both oxygen and a hydrogen evolution catalysts.
(1) Seitz, L. C.; Chen, Z.; Forman, A. J.; Pinaud, B. A.; Benck, J. D.; Jaramillo, T. F. ChemSusChem 2014, 7 (5), 1372-1385.
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