Surface passivation and point-defect control in Cu(In,Ga)Se <sub/>2</sub> films with a Na <sub/>2</sub> S post deposition treatment for higher than 19% CIGS cell performance

摘要： Na2S as a new alkaline source was employed to passivate the surface of CIGS film. Na2S has less formation enthalpy compared to alkali fluoride compounds leading to the more effective dissolution at the surface. An efficiency of 19.2% was obtained by post deposition treatment (PDT) with Na2S source for cell with anti-reflective coating and active area of a 0.43cm2. The remarkable performance enhancement compared to the efficiency of 16.64% of the cell without the PDT was due to the increase of Voc and FF. With the Na2S PDT, Na distribution in CIGS film was much shallower and the valence band lowering was smaller compared to that with NaF PDT. The emission intensity of low-temperature photoluminescence at 1.04 eV, which corresponds to electron transition from In-in-Cu (InCu) antisite to the valence band maximum, was greatly reduced by Na2S PDT compared to NaF PDT. The result suggests that in addition to lowering the Cu vacancy concentration, the concentration of InCu defects significantly decreased at the CIGS surface by Na2S PDT compared to NaF PDT. Our results indicated that the surface passivation by Na2S PDT was more effective than NaF PDT.