Environmental assessment of thin silicon solar cells from pilot production

Following the earlier demonstration of the performance capabilities of 4-mil silicon solar cells and the feasibility of using these cells on large flexible arrays of space vehicles, more than a thousand 4-mil cells have been fabricated in pilot production by four routes. The various types of cells that have been evaluated had solderless evaporated titanium-silver contacts in both a conventional and wraparound configuration, solderless evaporated titanium-silver contacts "overplated" with a layer of copper-gold, and solderless plated mickel-copper-gold contacts in a conventional and wraparound configuration. Both 1-by-2-cm and 2-by-2-cm, n on p cells have been manufactured from 1 and 10 Ω . cm boron-doped silicon. In every case, satisfactory production yields have been achieved. The above cells have been subjected to environmental conditions aimed at studying the effects of high-ambient humidity on the cell contacts during "shelf life" prior to launch and the degradation in performance from electron and proton irradiation encountered during long-term spiral transfer orbits to synchronous altitude. Specifically the problem of low-energy "synchronous altitude" proton irradiation of exposed bar and back contacts and the protection afforded by various forms of coatings has been investigated.