Roll-to-roll Equipment for Atmospheric Atomic Layer Deposition for Solar Applications

Roll-to-roll Equipment for Atmospheric Atomic Layer Deposition for Solar Applications

Raymond Knaapen
VPL

Spatial ALD enables deposition rates exceeding 1 nm/s, which enables increased throughput and decreased cost levels. As part of the EU FP7 project “R2R CIGS”, a second generation R2R ALD tool has been realized, aimed at deposition of zinc oxysulfide (Zn(O,S)) buffer layers in CIGS solar cells as replacement for CdS. The deposition of Zn(O,S) using ALD with premixing of precursors is enabled by spatial processing. The oxygen to sulfur ratio can be manipulated using variation of precursor premixing ratio in the gas supply as well as variation in exposure time. Using only DEZn and H2O it is possible to deposit intrinsic zinc oxide (i:ZnO), and by admixing H2S to H2O it is possible to obtain a Zn(O,S) compound, which is required for the CIGS buffer layer. The described R2R ALD tool has been used to apply buffer layers with various oxygen to sulfur ratios on CIGS stacks. Finalizing the stacks has resulted in functioning CIGS solar cells with promising efficiency values.