Time constants of open circuit voltage relaxation in Cu(In,Ga)Se2 solar cells

The time constants of metastable defect reactions in Cu(In,Ga)Se-2 solar cells are analyzed in a temperature range of 340 to 390 K. Both, the increase of the open circuit voltage V-oc during illumination as well as the subsequent relaxation of the junction capacitance C follow a stretched exponential behavior. The activation energies are about 0.6 eV for the V-oc increase and 1.0 eV for the capacitance decay, while the time constants exhibit a cross-over at a temperature of 360 K. The exponential factor decreases in both cases with increasing temperature, a behavior that is rather uncommon for systems exhibiting stretched exponential relaxation. (C) 2007 Elsevier B.V. All rights reserved.