Electrostatic potential fluctuations and light‐soaking effects in Cu(In,Ga)Se 2 solar cells
Résumé
In Cu(In,Ga)Se 2 (CIGS) thin-film solar cells, laterally inhomogeneous distributions of point defects may induce electrostatic potential fluctuations and thus reduce the open-circuit voltage (V oc). In the present work, we investigate possible origins of fluctuating potentials and estimate the amplitude of fluctuations and V oc 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-beam-induced current measurements were employed to study the local difference in the width of the space-charge region (w SCR). It is shown that the amplitude of fluctuations in the w SCR depends significantly on the choice of buffer system and on the duration of the RbF PDT. In addition, energy-dispersive X-ray spectroscopy and cat-hodoluminescence measurements reveal that band-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 cells.