Light soaking effects in Cu(In,Ga)Se2 superstrate solar cells

Cu(In,Ga)Se-2 superstrate solar cells with efficiencies of up to 11.2% have been developed. Sodium which is considered beneficial for superstrate solar cells, has not been added to the cells presented in this contribution. The open circuit voltage and fill factor of as-deposited cells increase when light soaked under an illumination of one sun. A large part of the efficiency improvement occurs within 1 h of illumination and the gains are maintained even when the cells are subsequently stored in dark for several days. Measurements of the junction capacitance revealed a low carrier concentration of similar to 1 x 10(14)/cm(3) in the absorber layer of as-deposited cells. After light soaking the carrier density increases by one order of magnitude which causes an increase in the open circuit voltage. Measurements of the quantum efficiency under operating conditions revealed that light soaking also improves the collection of carriers created by long wavelength photons. (C) 2003 Elsevier Science B.V. All rights reserved.