Characterisation of high-performance photovoltaic materials for space applications using a correlative cathodoluminescence/photoluminescence spectrosc

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In the context of photovoltaics for space applications, the term high-performance encompasses several material properties. A key requirement for the photovoltaic devices and one that ties together many of the desired material properties is that of high efficiency. The power supply to satellites is the limiting factor in the possible mission objectives and usually also determines their lifetime. It is therefore the need for materials that enable the fabrication of high efficiency devices, not only at the beginning of life, but also maintained despite the harsh conditions of space, that drives the research of this project.The project will explore two sides of this high efficiency problem, improvement of both efficiency at beginning of life as well as sustainability of on-mission performance. It will aim to do so through characterization of materials using cathodoluminescence and photoluminescence spectroscopy methods, which will improve our understanding of the optical and electrical properties of materials and give us the information to make vital improvements to materials or device structures.The current industry standard for space power systems is an on-wafer III-V multi-junction technology. In this project we will develop materials for an alternative high efficiency concept: the hot-carrier solar cell. This emerging device concept could enable high efficiency in a thin, comparatively simple and thermodynamically elegant design. We will use luminescence techniques to study hot carriers in semiconductors and quantum confined structures, including their thermalization and extraction. Advances in retardation of thermalization mechanisms coupled with improved efficiency of extraction of hot carriers could lead to a new, fundamentally different class of photovoltaics, with efficiencies beyond the Shockley-Queisser limit.We will also address the challenge of radiation damage in these materials which is the main cause of performance deterioration for space photovoltaics. Impinging radiation introduces defects in the absorber, which act as non-radiative recombination sites for photogenerated carriers and therefore lead to a decrease in device-efficiency and therefore performance. The experimental techniques identified above can be used to effectively study defect sites. The planned correlative approach, together with capacity for time-resolved measurements in both cathodoluminescence and photoluminescence spectroscopy may provide new insight on defects and their effects in novel device structures.