Reactively Sputtered Zn(O,S) Buffer Layer Suitable for Roll-to-Roll Fabrication of Cu(In,Ga)Se2 Devices

Abstract

One promising pathway to lower the dollar-per-watt ($/W) cost of CIGS PV is by transitioning the entire device fabrication process to high-throughput roll-to-roll (R2R) or sheet-to-sheet manufacturing. For the full realization of this goal, it is essential that each layer and process in the CIGS stack be optimized for throughput, uniformity, and low-cost operation and maintenance. In this work, Zn(O,S) films are deposited by RF reactive magnetron sputtering for evaluation as an R2R-suitable alternative buffer layer and compared to the industry standard CdS buffer layer deposited by chemical bath. ZnOS films are grown under a range of conditions and characterized by AES, UV-Vis, and XRD. A set of 35 10 cm × 10 cm 3-stage co-evaporated CIGS layers were grown on Mo coated soda lime glass (SLG) and split in half, with one half receiving a sputtered Zn(O,S) buffer layer, and the other half a baseline CdS deposited by chemical bath and a sputtered intrinsic ZnO (i-ZnO) bilayer. The devices were completed with Al:ZnO and Ni/Al grids, with no antireflective coating, then mechanically scribed to isolate 0.43 cm2 area sized cells. Analysis of the completed devices includes IV testing under simulated AM1.5 irradiance. Shunt resistance and series resistance are approximated based on IV curve data. The highest efficiency Zn(O,S) based device measured 10.0% while its control pair measured 12.8% with a CdS/i-ZnO bilayer.