No abstract

Transparent oxide back contact of Cu(In,Ga)Se 2 (CIGS) solar cells is crucial for semitransparent or bifacial CIGS photovoltaics. Parasitic GaO x resistive layer formed at the back junction, however, has been the bottleneck for transparent photovoltaic applications. Here, we show that a complementary control of the back junction enabled a high efficiency, semitransparent CIGS module. By employing a thin Ag precursor layer prior to CIGS evaporation, the back-junction barrier could be eliminated.Atomic probe tomography measurement suggests that an appreciable amount of Ag doping in the GaO x may form hole-tunneling channels at the back junction. We also found that potassium fluoride (KF) post-deposition treatment (PDT) increased the back-junction resistance and the bulk CIGS resistance compared to the case with Na PDT. The KF-induced increased resistances turned out to be beneficial for suppressing the parasitic shunt current along the P1-scribing region in our CIGS solar module. Interestingly, J-V rollover caused by the KF-induced back-junction barrier completely vanished after see-through laser scribing of the module. We attribute the barrier-lowering to a laser-induced local heating at the back junction. The complementary engineering strategy introduced here would allow functional oxide back contact in CIGS photovoltaic modules for both high efficiency and semitransparency.