Examining the role of ultra-thin atomic layer deposited metal oxide barrier layers on CdTe/ITO interface stability during the fabrication of solution processed nanocrystalline solar cells

• Solution processed CdTe solar cells show diffusion across the CdTe/ITO interface.
• Diffusion across the interface is detrimental for the performance of the solar cells.
• Metal oxide buffer layers at the CdTe/ITO interface eliminate diffusion.
• Metal oxide buffer layers at the CdTe/ITO interface improve performance.

Solution processed CdTe layers are a potentially low-cost alternative for use in thin-film solar cells. We have recently reported the use of such nanocrystalline layers within ITO/CdTe/ZnO/Al device architectures. One key concern with this type of device structure is the possibility of atomic scale interdiffusion between the ITO and CdTe layers, which can result in deleterious n-type doping of the CdTe layer. Rutherford Backscattering has been used to study the chemical composition across the ITO/CdTe interface as a function of thermal annealing temperature. Through these measurements we verify that interdiffusion is observed across the interface for annealing temperatures above 200 °C, and the extent of interdiffusion increases with temperature. Ultra-thin alumina, zirconia and titania layers deposited between the ITO and CdTe layers have been studied for their potential to act as a diffusion barrier. All investigated barriers successfully suppress interdiffusion. The outcomes of these compositional studies are directly compared to solar cells fabricated under analogous processing conditions, demonstrating improved cell performance.

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