Atmospheric spatial atomic layer deposition of ZnOS buffer layers for flexible Cu(In,Ga)Se2 solar cells

Zinc oxysulfide (ZnOS) is synthesized at atmospheric pressure in a laboratory-scale spatial atomic layer deposition setup by sequentially exposing the substrate to diethyl zinc and an H2O/H2S mixture, separated by a nitrogen gas curtain. The co-injection of H2O and H2S vapors in the same deposition zone enables an accurate control of the S/(O + S) ratio, the morphology, and the optoelectronic properties of the films. Next, the ZnOS deposition process is transferred to an industrial roll-to-roll spatial-ALD setup. ZnOS is applied as a buffer layer in flexible Cu(In,Ga)Se2 solar cells, instead of the commonly used CdS, achieving a best efficiency of typically 13% in small area cells (0.57 cm2) and 9.2% in flexible mini-modules (270 cm2). These results show the viability of atmospheric spatial-ALD as a new technique for roll-to-roll manufacturing of flexible photovoltaics modules based on a Cu(In,Ga)Se2 absorber.