Influence of Na on Cu(In,Ga)Se2 solar cells grown on polyimide substrates at low temperature: Impact on the Cu(In,Ga)Se2/Mo interface

Abstract

There are still open questions regarding the nature of the positive effect of the presence of Na on the performance of Cu ( In , Ga ) Se 2 based, chalcopyrite thin filmsolar cells, especially at low processing temperatures. Studying Cu ( In , Ga ) Se 2 thin film devices fabricated from low-temperature coevaporated absorbers on polyimide substrates by admittance and J-V-T measurements, characteristic properties are identified for different amounts of Na present during the growth. A roll-over behavior can be directly correlated with the Na-content. X-ray photoelectron spectroscopy shows the development of a MoSe 2 phase at the back contact of the device. Efficiencies of 15.1% with MgF 2 antireflection coating are demonstrated.