polycrystalline thin film tandem solar cells cascaded by ZnTe/ZnO interconnects

The present work focuses on the optimization of an interconnect junction for II-VI tandem solar cells. We have used ZnTe:N/ZnO:Al and ZnTe:Cu/ZnO:AI as interconnect junctions between a CdS/CdTe top cell and a CdS/HgCdTe bottom cell. Separate annealing studies of ZnTe:Cu show electrical and optical properties that are stable to 387°C when the ZnTe:Cu is sputter deposited at ∼320°C. J-V measurements show that the V_OC of the tandem cell with ZnTe:Cu is much lower (∼820 mV) than the V_OC of the tandem cell (∼1031 mV) with ZnTe:N. One of the possible reasons is the interdiffusion of Cu into CdS, probably making it intrinsic and changing the junction properties of the top cell. Quantum efficiency measurements of the tandem cell with ZnTe:N show that the current is limited by the bottom cell, while the current seems to be limited by both the top cell and the bottom cell in the case of the tandem cell with ZnTe:Cu/ZnO:AI as the interconnect junction.