The impact of controlled sodium incorporation on rapid thermal processed Cu(InGa)Se2-thin films and devices

The alkali content of Cu(InGa)Se₂ thin films fabricated by RTP on a dense molybdenum backelectrode is below the detection limit of ESCA. Starting from this virtually sodium-free case, alkali impurities are successively added in order to study their impact on film morphology and device performance. Two novel techniques have been developed to add sodium to the chalcopyrite thin film: (1) By shifting the stress of the Mo-backelectrode from compressive to tensile its alkali permeability increases and in consequence so does the alkali content in the CIGS film. (2) Adding sodium compounds directly to the Cu-In-Ga-Se precursor film controls the final alkali content in CIGS independent from the substrate. Along with the addition of sodium a significant increase in performance of CIGS/CdS/ZnO cells (1.85 cm² active area) was found that peaked at 13.2%