Cathode luminescence analysis of Cu(In,Ga)Se2 solar cells treated with thiourea solution

Abstract Cross-sectional cathode luminescence (CL) was performed on working Cu(In,Ga)Se 2 (CIGS) solar cells to clarify the mechanism behind the performance improvement of solar cells subjected to a thiourea treatment. The low panchromatic CL intensity at the depletion zone demonstrates that the existent electric field sweeps the carriers nearby, lowering their possibility of non-radiative and radiative recombination. Accordingly, the low CL intensity at grain boundaries are not necessarily caused by high non-radiative recombination rate if band bending is present. The photon energy mapping showed an emission distribution according to the double-graded bandgap profile. A blue shift in photon emission at the minimum bandgap area was observed for the thiourea-treated sample. We presume that S ions provided by the thiourea solution passivate subgap defects such as donor-type Se vacancies, resulting in radiative transitions with higher energies and higher net carrier density that eventually contributed to the higher fill-factor and higher open-circuit voltage.