Abstract
AbstractThis paper details 3 years of cadmium telluride (CdTe) photovoltaic performance onboard the AlSat‐1N CubeSat in low earth orbit. These are the first CdTe solar cells to yield I–V measurements from space and help to strengthen the argument for further development of this technology for space application. The data have been collected over some 17 000 orbits by the CubeSat with the cells showing no signs of delamination, no deterioration in short circuit current or series resistance. The latter indicating that the aluminium‐doped zinc oxide transparent front electrode performance remained stable over the duration. Effects of temperature on open circuit voltage (Voc) were observed with a calculated temperature coefficient for Voc of −0.19%/°C. Light soaking effects were also observed to increase the Voc. The fill factor decreased over the duration of the mission with a major contribution being a decrease in shunt resistance of all four of the cells. The decrease in shunt resistance is speculated to result from gold diffusion from the rear contacts into the absorber and through to the front interface. This has likely resulted in the formation of a deep trap state within the CdTe and micro shunts formed between the rear and front contact. Further development of this technology should therefore utilise more stable back contacting methodologies more commonly employed for terrestrial CdTe modules.
Highlights
Thin film cadmium telluride (CdTe) photovoltaics (PVs) are a welldeveloped technology for terrestrial applications but have previously been untested in space
This paper reports on 3 years in a low earth orbit (LEO) of the first operational CdTe solar cell to be deployed in space
Thin film flexible PVs for space applications are receiving an increasing amount of attention from both the research and industrial communities, and it is timely that we report on the 3-year inorbit performance of the CdTe on cover glass technology
Summary
Thin film cadmium telluride (CdTe) photovoltaics (PVs) are a welldeveloped technology for terrestrial applications but have previously been untested in space. Delamination, of thin film PV for space applications, has been considered to be of particular concern to the research community since a research programme, conducted by Dutch Space B.V., investigating thin film copper indium gallium diselenide (CIGS), on titanium foil, suffered delamination from the substrate at the interconnects when subject to the thermal cycling that might be encountered in space.[7] after these results, new interconnects were developed and a flight experiment conducted on the Delfi-C3, 3-unit CubeSat in a LEO.[8] The CIGS cells, on titanium foil, showed no signs of degradation over the initial 3-month monitoring period during which time they were subject to temperature changes of 70C twice a minute due to the quick rotation of the CubeSat and the cells' low heat capacity This demonstrated that the revised interconnect method had resolved the delamination issue.[8] More recently (2018), Ascent Solar Technologies, Inc. have developed a prototype flexible CIGS module, which has been delivered to the International Space Station for a 1 year in-orbit assessment of the technology.[9]. This paper sets out to evaluate the durability of the CdTe payload in the space environment, over the duration of the CubeSat mission, through analysis of the relative changes of the in-orbit cell performance
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