Heterojunction interface passivation strategy for Cu(In1-x,Gax)Se2 solar cell with nano-level engineering of Zn-based buffer structure via atomic layer deposition method

Abstract The global needs for ecological friendliness and sustainable development in the photovoltaic (PV) market have led to an increased demand to fabricate solar cells in an environmentally sound manner using nontoxic elements. In response to these requirements, in chalcogenide solar cell technology, researchers are attempting to replace the conventional CdS buffer. A potential replacement buffer material is ZnOS due to its direct, large, and tunable bandgap. Atomic layer deposition (ALD) can be effectively used to deposit ZnOS on Cu(In1-x,Gax)Se2 (CIGSe) absorbers, as this process allows the highly controlled thickness and composition, conformal coverage, inline compatibility, and relatively easier maintenance. However, CIGSe solar cells with an ALD grown ZnOS buffer usually suffer from the deficit of open circuit voltage (Voc), which limits power conversion efficiency (PCE). To overcome the limitation, ZnOS buffer structure with ZnS nanolayer is engineered for heterojunction interface passivation (HIP) and the role of ZnS nanolayer is investigated. The insertion of the ZnS nanolayer between ZnOS and CIGSe exhibits passivation effects at the heterojunction interface, thereby to enhance the solar cell performance owing to the realization of a more refined bandgap structure. Wide bandgap ZnS passivation thus demonstrates considerable potentials for being applied in other material systems.