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

Abstract

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 (Vp) 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.