PERSISTENT PHOTOCONDUCTIVITY IN CU(IN,GA)SE-2 HETEROJUNCTIONS AND THIN-FILMS PREPARED BY SEQUENTIAL DEPOSITION

A characteristic, reversible metastability is observed for Cu(In,Ga)Se -2 thin films and ZnO/CdS/Cu(In,Ga)Se-2 heterojunctions. Annealing at 80 degrees C leads to a decrease of the dark conductivity of the thin films by up to a factor of 2 at room temperature and several orders of magnitude when measured at lower temperatures. By exposure to light, the initial state can be re-established. This reenhancement of the dar k conductivity can be looked at as persistent photoconductivity. Admit tance measurements at Cu(In,Ga)Se-2 heterojunction solar cells display a reversible shift of the activation energy of a distinct dielectric loss peak ranging from 70 to about 160 meV upon illumination or anneal ing at 80 degrees C, respectively. We propose that both phenomena as w ell as commonly observed light-soaking effects of Cu(In,Ga)Se, solar c ells have a common origin. (C) 1998 American Institute of Physics. [S0 003-6951(98)01228-5].