Characterisation of thin film CdSeTe/CdTe solar cells

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Thin film CdsSeTe/CdTe photovoltaic (PV) devices are the most successful second-generation technology with over 9GW produced in 2022. The efficiency of thin-film PV is limited by atomic-scale defects in the material (grain boundaries, planar defects, point defects etc). The manufacture of a high efficiency cell typically requires some form of defect passivation treatment. Examples include activation of CdTe by annealing in CdCl2, passivation of grain boundaries by chlorine, passivation of grain interiors by selenium etc.... Recent work at Loughborough using HRTEM has shown that as deposited CdTe contains high densities of stacking faults and that these are removed by the CdCl2 activation process. Work using EBSD has shown that randomisation of the grain structure is important. Cathodoluminescence (CL) is a powerful technique that shows how defects, impurities or microstructure can affect luminescence at the nanoscale. A new capability in CL is being developed at Loughborough with facilities on SEM and on a new dedicated STEM instrument. This project aims to determine how atomic-scale defects degrade cell efficiency and the fundamental mechanisms underpinning their passivation. A variety of techniques will be used including electron microscopy and the new CL capability. Suitable devices will be fabricated in the Photovoltaics Materials and Devices group in the Centre for Renewable Energy Systems Technology (CREST). We will also work with our long-term collaborators at the National Renewable Energy laboratory (NREL), Swansea University and with industrial partners. This project will be part of a special relationship with CTF Solar GmbH who will provide devices fabricated in their R&D facility in Germany.