Defects and recombination kinetics in copper indium gallium sulfide thin films with spatially resolved luminescence in the μm-scale

摘要

Chalcopyrite Cu(In,Ga)S_2 is a promising absorber in thin film solar cells, although the comparable high band gaps so far do not correspond to equivalent high open circuit voltages. We have performed photoluminescence studies on CdS passivated absorber layers deposited on Mo coated soda lime glass. From spectrally and spatially resolved (≤ 1 μm) room temperature photoluminescence measurements we have extracted the local splitting of quasi-Fermi levels (E_(Fn)-E_(Fp)) and local absorption (A(ω)) particularly in the sub bandgap-regime via Planck's generalized law. We observe a substantial negative correlation coefficient between the local sub bandgap/defect absorption and the local (E_(Fn)-E_(Fp)), which we interpret in terms of the recombination ofphotogenerated minority carriers (here electrons) via sub bandgap states/deep defects. Moreover we have correlated local PL yields with corresponding values at neighbor sites versus distance (increment analysis). As we find lateral correlation distances in the vicinity of average grain sizes we conclude grains with PL yield and according different splitting of (E_(Fn)-E_(Fp)) to be independent from one another and be laterally distributed randomly.