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

Abstract We report on the growth of highly conducting p-μc-Si:H films by hot-wire CVD. A systematic variation of the doping gas (trimethylboron) ratio was first carried out. High dark conductivity, σ D ≈1.0 Ω −1 cm −1 and low activation energy of dark conductivity, E a ≈62 meV have been achieved for thick films. For thin films ( d ≈20 nm), σ D ≈4.7×10 −2 Ω −1 cm −1 and E a ≈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 ≈2 nm) was grown for preparation on TCO-coated substrates prior to the deposition of the p-μc-Si:H layer. The incorporation of a p-μc-Si:H layer into 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 parameters for p-i-n and μc-Si/c-Si heterjunction solar cells are J sc =12.3 mA cm −2 , V oc =873 mV, FF=72%, η=7.8% and J sc =26.6 mA cm −2 , V oc =532 mV, FF=74%, and η=10.6%, respectively. To the best of our knowledge, these are the first heterojunction solar cells with the p-μc-Si:H emitter grown 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.