Efficient Solar Water Splitting with a Composite n-Si/p-CuI/n-i-p a-Si/n-p GaP/RuO2 Semiconductor Electrode

A composite semiconductor electrode with the structure n-Si/p-CuI/ITO/n-i-p a-Si/n-p GaP/ITO/RuO2 was fabricated for the purpose of achieving efficient solar water splitting. The electrode showed a stable photoanodic current due to oxygen evolution with a large negative photoshift (V-p) of about 2.2 V from an anodic current at a RuO2 electrode. The photoshift was large enough for full water splitting. A photoelectrochemical (PEC) cell, composed of the composite electrode, a Pt counter electrode, and 0.10 M Na2SO4 (pH 6.3), generated a photocurrent density of 1.88 mA cm(-2) under simulated solar illumination (AM 1.5 G, 100 mW cm(-2)), yielding a solar to chemical conversion efficiency of 2.3% as calculated from the photocurrent value. The result has shown that the combination of crystalline Si/a-Si/GaP is suitable for efficient solar water splitting. It is shown that the efficiency can be increased by use of GaP with a well-regulated p-n junction.