Electroabsorption Measurements on Bifacial CIGS Solar Cell Devices

Abstract

AbstractWe report the first studies of electroabsorption in Cu(InGa)Se2(CIGS) solar cell devices. We utilized a bifacial CIGS device with a Ga/(In+Ga) ratio of 0.8 (bandgap of 1.5 eV) deposited onto semi-transparent (40 nm thick) Mo coated glass as the back contact. By modulating the electric field using a small sinusoidal potential of amplitude δV across the CIGS layer, we were able to detect the modulation ΔT of the transmitted light. This was examined as a function of photon energy, DC bias, temperature, and modulation frequency (100 Hz to 10 kHz) and had a maximum amplitude of ΔT/T ≈ 10−5for δV = 0.3 V. Very different characteristics were obtained for near bandgap light (1.3 eV) compared to photon energies considerable smaller (<0.95 eV). While the latter exhibited a strong temperature and frequency dependence, indicating an important role for deep defects in the effect, the former exhibited very little change with temperature or frequency, indicating the predominance of transitions involving bandtail states. Different metastable states of the CIGS layer produced by prolonged light soaking above the bandgap energy were also examined.