High Photoelectrochemical Oxygen and Hydrogen Evolution Performance by Using a-Si/c-Si Heterojunction Solar Cells as Photoelectrodes

Si heterojunction (SHJ) solar cells, consisting of ultrathin amorphous Si (a-Si) layers on crystalline Si (c-Si), are designed as a photoanode or a photocathode by simply switching the polarity. Critical to enhance the performance of photoelectrodes is good surface passivation. Good surface passivation reduces photocarriers recombination, directly improving the open-circuit voltage (V_OC). Moreover, the optical losses by catalysts can be solved by separating the PV from the water redox reaction. The low recombination of photoelectrodes is critical to successfully achieve this design to avoid the photogenerated carrier recombination loss during the period of transport through the whole devices to participate in water redox reaction. The thin a-Si:H layers of SHJ solar cells served as not only the power generating layers but also good passivation layers, including chemical passivation and field-effect passivation. In this feature, we demonstrated the operation of an efficient and stable SHJ photoanode and photocathode. The SHJ photocathode displays excellent hydrogen evolution performance with a  of 0.640 mV,  of 33.49 mA/cm², where  is the onset potential measured at water reduction current density of 1 mA/cm⁻²,  is the equilibrium water reduction potential in 1 M H₂SO₄ solution, and  is the current density at , and a solar to hydrogen conversion efficiency (SHCE) of 13.26%, which is the highest ever reported for Si-based photocathode.