Electrostatic potential fluctuations and light amp; 8208;soaking effects in Cu In,Ga Se2 solar cells

In Cu In,Ga Se2 CIGS thin amp; 8208;film solar cells, laterally inhomogeneous distributions of point defects may induce electrostatic potential fluctuations and thus reduce the open amp; 8208;circuit voltage Voc . In the present work, we investigate possible origins of fluctuating potentials and estimate the amplitude of fluctuations and Voc losses in solar cells with various [Ga] in the CIGS absorber, with different buffer layers and with different durations of an RbF postdeposition treatment PDT . Electron amp; 8208;beam amp; 8208;induced current measurements were employed to study the local difference in the width of the space amp; 8208;charge region wSCR . It is shown that the amplitude of fluctuations in the wSCR depends significantly on the choice of buffer system and on the duration of the RbF PDT. In addition, energy amp; 8208;dispersive X amp; 8208;ray spectroscopy and cathodoluminescence measurements reveal that band amp; 8208;gap fluctuations do not have substantial impact on the device performance. Finally, some of the investigated cells were exposed to light soaking, which was found to be a means to reduce the detected electrostatic potential fluctuations and also to increase the effective electron diffusion length in the CIGS absorber for a part of the investigated cell