Fabrication,Structure Characterization And Photoelectric Properties Of Si-based Nanometer Thin Film Photovoltaic Materials

The intrinsic nc-Si:H films are deposited on glass, quartz and c-Si substrates by radio frequency plasma enhanced chemical vapor deposition(RF-PECVD), using H2 diluted Si H4 as reactive gas sources. The influences of substrate temperature, radio frequency power and Si H4 concentration on the structure and optoelectrical properties of the films are studied. The results show that nc-Si:H films with suitable crystallinity have higher optical absorption coefficients, good light stability and photosensitivity.High quality doped nc-Si:H films have been fabricated and the effects of dopant concentration on their structures, electrical and optical properties are studied. The experimental results show that high electrical conductivity can be obtained under appropriate P-doping content. When the ratio of [PH3] to [Si H4] is 1.0%, the conductivity of nc-Si(P):H film is ~5.4 S/cm. The lower B-doped nc-Si:H thin film have wider optical gap and lower resistivity. When the ratio between [B2H6] and [ Si H4] is 0.1%, the conductivity is ~1.2×10-3 S/cm and the optical band gap is ~2.05 e V.The α-Si:H/α-Si C:H multilayer films are prepared on c-Si and quartz substrates by PECVD system, using H2 diluted CH4 and Si H4 as reaction gas sources. The nc-Si:H/α-Si C:H multilayer films with controlled crystallite size are achieved by annealing α-Si:H/α-Si C:H multilayer films at high temperatures. As the longitudinal dimensions of the Si nanocrystallites are reduced from 10 nm to 2 nm, the optical absorption edge of nc-Si:H/α-Si C:H multilayer films occurs blueshift and the corresponding optical band gaps of multilayer films are increased from ~1.2e V to ~2.05 e V. At room temperature, the obvious negative differential conductivity phenomena are observed in the α-Si:H/α-Si C:H multilayer films, which is attributed to the sequence resonant tunneling occurred in the multilayer films. And as the electric field strength is greater than 0.38MV/cm, the Fowler-Nordheim tunneling processes are measured in the nc-Si:H/α-Si C:H multilayer films.A set of p-i-n type nc-Si:H thin film solar cells with different i-layer thickenss are fabricated by adopting optimized process conditions. Experimental results show that relatively good photovoltaic properties can be obtained at suitable i-layer thickness.