Identifying Suitable Front Contacts for Cd(Se, Te) Solar Cells on Space-Qualified Cover Glass

To employ solar cells in space, achieving high specific power (W/kg) and radiation hardness is crucial. CdTe thin-film solar cells are expected to demonstrate the capability of achieving high specific power and radiation hardness comparable to Si and III-V solar technologies, which currently dominate in space applications. Although CdS/CdTe solar cells have been studied extensively for performance degradation, and somewhat for radiation tolerance, the more modern, higher efficiency architecture based on Cd(Se, Te) (CST) remains relatively unexplored for space application. The maximum efficiency achieved by CdTe-based solar cells under standard terrestrial test conditions is 23.1% at the laboratory scale. However, for terrestrial applications, CdTe is generally deposited on commercially available fluorine-doped tin oxide (FTO)-coated ~3 mm thick glass substrates. Because ultra-thin and lightweight glass substrates do not come with a transparent conducting oxide (TCO) layer, the TCO and emitter choice becomes crucial. Here, we report the fabrication of CST solar cells, based on multi-source evaporation, on space-qualified cover glass, with a matrix of different front TCOs and emitters to determine the optimum working combination for high-efficiency superstrate-configured CST solar cells on thin glass substrates. The aim is to monitor the effects on UV transmission, while balancing it with the sheet resistance, determine their stability to high temperature and reactive ambients in the processing, and then calculate figure of merit to determine the quality of TCOs. The device structure will then be optimized to achieve maximum device performance under AM0 atmospheric conditions with minimal losses compared to that under the AM1.5G condition.