Dye-sensitization observed in photoelectrochemically etched n-type gallium nitride

Abstract

The sensitization in visible light region is observed by the adsorption of N3 (bis [(4,4'-dicarboxy-2,2'- bipyridyl)(NCS)] Ru(II)) dye on photoelectrochemically etched n-GaN surface. From the incident photon to current efficiency spectrum, the sensitization in visible light region and its enhancement with the increase of surface roughening is observed, but the sensitization decreases by the excess etching. From the excitation intensity dependence of photocurrent at 546 nm wavelength, the electron transfer from the excited N3 dye to n-GaN occurs via one-photon process, not via intermediate states. The solar cell is fabricated using I2/LiI in acetonitrile as the electrolyte and Pt sputtered fluoride tin oxide glass as the counter electrode. According to the solar simulator measurement at AM1.5G, the short-circuit current density and the conversion efficiency are 0.6 mȦcmTiO-2 and 0.27%, respectively. The low adsorbed dye amount on the etched n-GaN surface is the cause for these small current and efficiency values, but the current per adsorbed N3 dye molecule is comparable with the N3 dye/TiO2 nano-porous layer system by BET surface area measurement and dye dissolution experiment. To reflect wide-bandgap of GaN, the open-circuit voltage of 0.71 V and the fill factor of 0.64 are also comparable with the dye-sensitized solar cells using TiO2 nano-porous layer.