Substrate influences on CIS device performance

It has been reported that the substrate plays an active role in copper indium diselenide (CIS) devices. The physical properties of the substrate, i.e., thermal expansion coefficient, chemical composition, strain point, surface quality and cleanliness may all play a role in device efficiency and process reproducibility. For example, sodium is known to influence the conductivity of CIS, and that soda lime glass (SLG) introduces sodium into the CIS. In the experiments reported here, the sodium level in the CIS was varied by (a) changing the substrate composition and (b) the use of SiO_xN_y and SiN_x barrier layers. Solar cells were fabricated on the candidate substrate and barrier layer combinations. V_oc was observed to drop with the addition of barrier layers to sodium containing glasses. The films were also analyzed for sodium by SIMS. The cell performance and SIMS analysis are presented and their significance is discussed