NANOCRYSTALLINE PHOTOELECTROCHEMICAL CELLS - A NEW CONCEPT IN PHOTOVOLTAIC CELLS

Semiconductor films with small crystal size normally exhibit prohibitively large recombination losses in photovoltaic cells. We show that porous nanocrystalline films of CdS and CdSe can be used as photoelectrodes in photoelectrochemical cells with relatively low recombination losses. Spectral response measurements show how the recombination losses depend on film thickness. These photoelectrochemical cells operate due to charge separation at the semiconductor-electrolyte interface rather than by a built-in space charge layer as normally occurs in photovoltaic or photoelectrochemical cells. The rapid removal of one charge by the electrolyte explains the low recombination loss. The mechanism of these photoelectrochemical cells regarding the direction of photocurrent flow and the value of photovoltage is discussed.