Regensburg 2004 – scientific programme

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DS: Dünne Schichten

DS 19: FV-internes Symposium „Dünne Schichten für die Photovoltaik I“

DS 19.1: Invited Talk

Thursday, March 11, 2004, 09:30–10:10, HS 32

Thin-film photovoltaics with crystalline Si using porous Si for layer transfer (PSI process) — •Rolf Brendel, Heiko Plagwitz, and Richard Auer — Bavarian Center for Applied Energy Research (ZAE Bayern), Am Weichselgarten 7, D-91058 Erlangen, Germany

Thin-film photovoltaics aims at replacing 300 micron thick wire-connected crystalline Si wafers by at least 10 times thinner modules that have an integrated series connection. This talk reviews a largely unexplored approach to fabricate thin-film modules by using layer transfer with porous Si (PSI process).

We porosify the surface of a Si substrate by anodic etching. The porous Si layer is monocrystalline and permits the homoepitaxial growth of a Si film. The porous surface layer becomes mechanically weak during annealing and thus a transfer of the epitaxial film to a glass carrier is possible. The growth substrate is re-used to fabricate further cells. We achieve an independently confirmed power conversion efficiency of 15.4 percent with a 25 micron thick cell that is processed without using photolithography.

Layer transfer enables novel technologies for implementing an integrated series connection, since both sides of the epitaxial film are freely accessible for processing. We introduce a module design that interconnects adjacent cells by a single metallization step. A first implementation of this scheme yields a module efficiency of 10.0 percent.

Good surface passivation is vital for thin cells. We demonstrate a novel low-temperature process to passivate and locally contact thin-film solar cells. The average surface recombination velocity of the contacted rear side is 100 cm/s.