An analysis of the effect of illumination to the reverse and forward bias current transport mechanisms in an efficient n-ZnO/n-CdS/p-Cu(In,Ga)Se2 solar cell

Temperature dependent current–voltage measurements are used to determine the effect of white light illumination on the dominant current transport mechanism in an efficient n-ZnO/n-CdS/p-Cu(In,Ga)Se2 heterojunction solar cell. The forward J–V characteristics are modelled by double exponential expression. In the dark, the forward current transport is mainly dominated by recombination at interfacial regions with pronounced tunnelling effect. Nevertheless, approximately above 200 K, the thermal dependence of the diode parameters in the second junction interface can be explained in terms of properly increasing contribution of pure depletion region recombination mechanism. Under white light illumination, the forward current is still dominated by the tunnelling enhanced interface recombination mechanism with considerably enhanced tunnelling contribution. The presence of a significant distortion observed below 180 K is attributed to the shift of Fermi level at junction interface and recharge distribution in the junction region due to metastable nature of the defect states. Below and above than 230 K, the reverse bias current transport in the dark is described by using space charge limited current and a thermally activated behaviour, respectively. Under illumination the variation of temperature dependent reverse current with voltage suggests that either the SCL current in the velocity saturation regime or tunnelling dominates the current transport.