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2009
Conference Paper
Titel
18.8% EWT-cells with screen-printed metallization and single step side selective emitter formation
Abstract
A fabrication process for EWT-cells on monocrystalline material with high quality gap passivation by wet thermal silicon dioxide is investigated. Masking steps are performed by screen-printing and via-holes are created by highspeed laser drilling. The screen-printed aluminum paste is found to penetrate the underlying thermal dioxide layer at appropriate contact firing conditions leading to a zone of high recombination in the overlap region of aluminum and silicon dioxide. It is shown that conventional PECVD-anti-reflection silicon nitride acts as effective protection layer reducing the recombination in this region. A selective doping structure fabricated in a single high temperature step allowing for a high via-hole conductivity, the use of silver paste to establish the contact on the rear side and a high quantum efficiency in the low wave-length range is introduced. Therefore either doped or undoped PECVD silicon dioxide layers are deposited on the front side, and it is shown that advantageous doping profiles can be achieved. Conversion efficiencies up to 18.8% on FZ material are obtained applying the single step side selective emitter fabrication technique.
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