The influence of Na on low temperature growth of CIGS thin film solar cells on polyimide substrates

• DOI: 10.1016/j.tsf.2008.10.085
• Publication Date: 2008-11-11T02:36:40Z
• Authors: R. Caballero; C.A. Kaufmann; T. Eisenbarth; M. Cancela; R. Hesse; T. Unold; A. Eicke; R. Klenk; H.W. Schock
• Keywords: 0103 physical sciences; 02 engineering and technology; 0210 nano-technology; 01 natural sciences; 7. Clean energy

Abstract The objective of this work is to study the influence of Na on the properties of Cu(In,Ga)Se 2 (CIGS) absorber layers and finished solar cell devices on polyimide substrates. For this study Na is added to 3-stage grown CIGS thin films by evaporation of a NaF precursor layer prior to the absorber deposition. The precursor layer modifies the CIGS growth kinetics. A stronger Ga-gradient and a decrease of grain size are observed when the Na content increases. An increase in V oc for a higher Na concentration at a nominal growth temperature of T sub,max = 500 °C during CIGS deposition is explained by a higher carrier density, as obtained by DLCP measurements. The higher carrier concentration for the higher Na content could be attributed to the reduction of a compensating donor. However, a low J sc does not allow for an enhanced efficiency possibly due to a shorter depletion region, as observed by admittance spectroscopy, and effective diffusion length.