Bifacial Micropyramidal Surface for Achieving High Efficiency of Photoelectrochemical Water Splitting

Photoelectrochemical splitting of water into hydrogen and oxygen are of great interest for the production of clean and storable form of chemical fuels. Silicon, the most investigated material as the photoelectrode has the potential for both the dual-absorber and tandem photoelectrochemical system. However, a major inadequacy in simultaneous achievement of efficiency, electrochemical stability, and the photon management hinders the practical prototype based on Si. Herein, we have successfully addressed the issues in band-structure engineering, light harvesting, and photon management in Si heterojunction (n + p-Si) photocathode for the concurrent improvement in the photon management, efficiency and stability. The resultant state-of-the-art Si heterojunction (n + p-Si) photocathode exhibits the current density of 61.2 mA/cm 2 that yielded the solar-to-hydrogen conversion efficiency of 18.22% for the bifacial design, with the electrochemical stability over 370 h, the highest efficiency and stability reported so far on single junction Si-based photocathodes. Moreover, the surface structured photocathode demonstrates the excellent bifacial and omnidirectional light harvesting capability over a wide angle of about 180°, as compared to conventional single-sided devices that can absorb only <50° over an entire rotation. The high efficiency, chemically stable and bifacial photoelectrochemical cell demonstrated herein can provide a significant advance towards the development of next-generation renewable energy devices.