Role of planar defects in Cu(In,Ga)Se2 thin-film solar cells

摘要

Thin-film solar cells with polycrystalline Cu(In,Ga)Se2 absorber layers exhibit record power-conversion efficiencies of currently 22.6%. Such performance is impressive in view of the rather small average grain sizes of 0.5-1. μm with Cu(In,Ga)Se2 layer thicknesses of 2–3 μm, The present work gives insight to the chemistry at planar defects (stacking faults and grain boundaries) in Cu(In,Ga)Se2 absorber with and without Na doping by using correlative microscopy approach. Surprisingly, the planar defects in the Na-free absorber show strong In, Se-enrichment and Cu-depletion. This is contrary to what have been observed for the planar defects in Na-containing absorber, i.e. very weak In-enrichment and Cu-depletion accompanied by Na segregation. This work clearly proves that Na does not only act as a dopant, but also as a passivator inside the Cu(In,Ga)Se2 absorber layer, explaining in this way his undoubtful beneficial effect on the cell performance.