Studies of photocorrosion and passivation of n-GaAs based semiconductor/liquid junction photoelectrochemical cells

Semiconductor photoelectrochemical cells offer a cheap, easily constructed alternative to all-solid-state solar cells. However, a persistent problem in their development has been photocorrosion of the semiconductor electrode. Photocorrosion degrades the electrode, reducing the device lifetime to unacceptably short times.; Much effort has gone into developing passivation schemes to reduce or eliminate photocorrosion. None has yet provided permanent protection. A better understanding of the basic interfacial chemistry and physics is necessary to achieve this. Toward this end, the studies described in this manuscript have been performed.; n-GaAs has been chosen as the electrode material in these studies due to its strong absorption near a maximum in the solar spectrum. Its photoelectrochemical behavior in Na{dollar}sb2{dollar}S has been examined because of the known ability of Na{dollar}sb2{dollar}S to passivate photocorrosion. Although the protection provided by Na{dollar}sb2{dollar}S is known to be temporary, the focus of these studies is to gain a more complete understanding of the interactions between Na{dollar}sb2{dollar}S and GaAs which lead to passivation and photocorrosion.; Three separate studies are described in this manuscript. In the first, time-resolved photoluminescence experiments were employed to determine whether the minority carrier surface recombination velocity (SRV) is dependent upon electrolyte concentration. The results indicate that, within the concentration range studied, the SRV is independent of Na{dollar}sb2{dollar}S concentration, suggesting that there is no significant change in the degree of semiconductor/electrolyte bond formation.; In the second study, the dependence of photocorrosion and passivation on crystallographic orientation was examined. Results show that the (100) and (110) surfaces of GaAs were passivated equally well by Na{dollar}sb2{dollar}S, although surface states which eventually formed at the two surfaces were separated in energy by 300 meV. The (111)B surface was not passivated by Na{dollar}sb2{dollar}S.; In the third study, the degree of {dollar}rm Assb2Ssb3{dollar} and {dollar}rm Assb2Osb3{dollar} formation on Na{dollar}rmsb2S{dollar} coated electrodes was measured as a function of crystallographic orientation using X-ray Photoelectron Spectroscopy. The (100) and (110) surfaces were found to have significant {dollar}rm Assb2Ssb3{dollar} formation, whereas the (111)B surface forms negligible amounts of {dollar}rm Assb2Ssb3{dollar}, indicating that the formation of interfacial sulfides plays a dominant role in the passivation of photocorrosion of n-GaAs.