Open-circuit and doping transients of Cu(In,Ga)Se2 solar cells with varying Ga content

Solar cells based on Cu(In1-x, Ga-x)Se-2 typically show time transient behavior of the open-circuit voltage V-oc under illumination. In this work, we study both the red-light V-oc(t)transient and the red-light capacitance transient at different temperatures of samples with different x. From the capacitance transient, we calculate a transient behavior of the Cu(In1-x,Ga-x)Se-2 doping density N-A,N-a(t). Then, using established models on the N-A,N-a dependence of the dominant recombination mechanisms, we derive from V-oc(t)that Cu(In1-x,Ga-x)Se-2 samples with x = 0, 0.3 are dominated by bulk recombination and a sample with x = 1 is dominated by interface recombination-in agreement with the expectation. Further, the transients of N-A,N-a(t)can be used to recalculate V-oc(t)transients which are then compared with the measured V-oc(t)transients. From the excellent agreement, we conclude that under red-light illumination V-oc(t)indeed is dominated by N-A,N-a(t)and other transient effects are of secondary importance. We further conclude that the sample with x = 1 can be described by an absorber/buffer/window energy band diagram with fully depleted buffer layer which here is CdS. (C) 2015 AIP Publishing LLC.