Current status of the thermo-catalytic (hot-wire) CVD of thin silicon films for photovoltaic applications

Thermo-catalytic (TC) or hot-wire (HW) chemical vapor deposition (CVD) is a promising technique for growing amorphous and microcrystalline silicon fil ms with improved stability and high rates. In this paper we report an the p hotovoltaic (PV) applications of thin silicon films deposited by this metho d. After a short review of the history of PV applications of TCCVD, from th e be.-inning in 1993, the main part of the paper deals with our research an d development of films and interfaces needed for the fabrication of differe nt solar cell structures entirely by TCCVD. So far, our highest conversion efficiency is eta = 10.2% for a pin structure, containing only an intrinsic a-Si:H film deposited by TCCVD. Depositing the whole pin structure entirel y by TCCVD, we have obtained eta = 8.8% until now. After development of a t unnel junction, the first tandem solar cell device, a stacked pin-pin struc ture has been recently produced showing eta = 7%. First attempts have been made for large-area deposition. In a 30X30 cm(2) batch system, a-Si:H films with device grade photoelectronical properties and high thickness uniformi ty can be produced at a high rate of 6 Angstrom /s. When incorporating i-la yers from this system into pin solar cells, a conversion efficiency of eta = (6.4 +/-0.8)% was obtained on an area of 20X20 cm(2). Finally, we report on silicon wafer-based solar cells, where a-Si, Lc-Si and epi-Si film emitt ers were deposited by TCCVD showing conversion efficiencies up to eta = 15. 2%. (C) 2001 Elsevier Science B.V. All rights reserved.