Growth of device quality p-type mu c-Si : H films by hot-wire CVD for a-Sipin and c-Si heterojunction solar cells

We report on the growth of highly conducting p-pc-Si:H films by hot-wire CV D. A systematic variation of the doping gas (trimethylboron) ratio was firs t carried out. High dark conductivity, sigma (D) approximate to 1.0 Ohm (-1 ) cm(-1) and low activation energy of dark conductivity, E(a)approximate to 62 meV have been achieved for thick films. For thin films (d approximate t o 20 nm), sigma (D)approximate to4.7X10(-2) Ohm (-1) cm(-1) and E(a)approxi mate to 80 meV were obtained. The annealing characteristics of thick films show thermally assisted dopant activation. Microcrystalline growth in these films was verified by XRD. A very thin p-a-Si:H seed layer (d approximate to2 nm) was grown for preparation on TCO-coated substrates prior to the dep osition of the p-muc-Si:H layer. The incorporation of a p-muc-Si:H layer in to a-Si:H p-i-n solar cells has improved the open circuit voltage (870-900 mV) relative to the use of a p-a-SiC:H layers. At present the best I-V para meters for p-i-n and muc-Si/c-Si heterjunction solar cells are J(sc)=12.3 m A cm(-2), V-oc=873 mV, FF=72%, eta =7.8% and J(sc=)26.6 mA cm(-2), V-oc=532 mV, FF=74%, and eta =10.6%, respectively. To the best of our knowledge, th ese are the first heterojunction solar cells with the p-muc-Si:H emitter gr own by HWCVD. The necessity of a seed layer has been found to be very much important in both types of solar cells. Two different types of seed layers, and their thickness variation, were also investigated. (C) 2001 Elsevier S cience B.V. All rights reserved.