Photoelectrolysis of Water in Sunlight with Sensitized Semiconductor Electrodes

In all previous studies of the photoelectrolysis of water, very little attention has been paid to the carrier generation and transport properties of the optically active semiconductor electrode. To gather such information the present work theoretically analyzes the spectral response of photoelectrolysis cells. Comparison with experimental results allows us to determine the diffusion length of minority carriers in for the first time. It is the hole transport that governs the spectral response curve, not the electron transport. The quantum efficiency of carrier generation in electrodes in the photolysis mode can be increased to 80% by doping the crystals with Al. The sunlight conversion efficiency has been raised to 1.3% from 0.4% reported earlier by others. The spectral response of the device has been extended into the visible portion of the spectrum through sensitization of the with Cr dopant impurities, allowing hydrogen generation with visible light. The photoelectrolytic processes associated with the impurity doped crystals are discussed.