A time-resolved microwave conductivity study of the optoelectronic processes in Ti O2 ∫ In2 S3 ∫ CuIn S2 heterojunctions

Abstract

Photoinduced interfacial charge carrier generation, separation, trapping, and recombination in Ti O2 ∫ In2 S3 ∫ CuIn S2 cells have been studied with time-resolved microwave conductivity (TRMC). Single layer, double layer, and complete triple layer configurations have been studied. Selective electronic excitation in one of the components is accomplished by using monochromatic pulsed laser excitation. In bare CuIn S2 films and in Ti O2 ∫CuIn S2 double layers, photoinduced charge carriers recombine on a subnanosecond time scale. This fast recombination slows down significantly when an In2 S3 buffer layer is applied between Ti O2 and CuIn S2. In that case, the charge separation lifetime increases by more than one order of magnitude. A superlinear dependence of the TRMC signals on the incident laser intensity is observed for the triple layer configuration, which indicates saturation of electron traps in In2 S3 or hole traps in CuIn S2. Furthermore, TRMC signals from Ti O2 ∫ In2 S3 ∫ CuIn S2 triple junctions and those from In2 S3 ∫CuIn S2 double layers are identical, which shows that charge carrier separation exclusively takes place at the In2 S3 ∫CuIn S2 interface. © 2007 American Institute of Physics.