Alexandre Michel Mayolet

Record Voc-Values for Thin-Film Polysilicon Solar Cells on Foreign Substrates using a Heterojunction Emitter

Thin-film polysilicon solar cells on foreign substrates are often considered as a promising low cost alternative to bulk silicon solar cells. Until now however, the obtained efficiencies and open-circuit voltages are far below those of other technologies. In this paper, we show how the open-circuit voltage can be enhanced significantly using an amorphous silicon-crystalline silicon heterojunction emitter instead of a diffused homojunction emitter. Open-circuit voltages up to 536 mV were obtained for polysilicon layers with a heterojunction emitter. This is the highest open-circuit voltage obtained for polysilicon solar cells with a p-n structure on foreign substrates

Thin-film monocrystalline-silicon solar cells on transparent high-temperature glass-ceramic substrates

Solar modules made from thin-film crystalline-silicon layers of high quality on glass substrates could lower the price of photovoltaic electricity substantially. One possibility is to use polycrystalline-silicon thin films, but the difficulty of this approach is to obtain a sufficiently high material quality and to achieve an effective passivation of the numerous grain boundaries. However, the utilization of a monocrystalline-silicon thin film instead of a polycrystalline-silicon layer should enable simpler device processes, higher process yield and a single-crystal-like efficiency due to the intrinsic higher quality of the material. In this paper, 10-micron thick monocrystalline-silicon layers on transparent glass-ceramic substrates were made by epitaxial thickening of thin monocrystalline-silicon seed layers. By using a very simple cell structure that does not incorporate any light trapping features, silicon single-crystal solar cells on glass-ceramics presented efficiencies of up to 7.5%. However, efficiencies above 9% should be realizable by simply improving the contacting scheme. In addition, by integrating an efficient light trapping scheme and by optimizing the minority carrier diffusion length, the efficiency potential could be as high as 15% for films with a thickness between five to ten microns on glass-ceramics.