Influence of heavy alkali post deposition treatment on wide gap Cu(In,Ga)Se2

The effect of Potassium, Rubidium, and Cesium post deposition treatment (PDT) on wide bandgap Cu(In,Ga)Se-2 (CIGSe) absorbers has been investigated. The results show that the efficiency of the cells can be improved by the alkali treatment and a higher value of the open-circuit-voltage (V-OC) can be achieved. In spite of this improvement, the activation energy (E-A) of the treated samples remained smaller than the bandgap (E-g) and V-OC(t) transients under red light showed a negative slope. Hence, the wide gap CIGSe devices remain limited by recombination at the interface. However, the V-OC(t)-transient of treated and untreated samples with the same E-g show a different slope (d Delta V-OC(t)/dt). CIGSe samples treated with heavy alkalis (RbF-and CsF-PDT) illustrate a smaller slope in comparison to no-PDT and KF-PDT samples. In this contribution, we discuss the V-oc(t) slope, i.e. d Delta V-OC(t)/dt, with reference to the illumination dependent doping density (N-Delta,N-a) and to a possible Sodium exchange mechanisms.