Optimisation of microcrystalline silicon deposited by expanding thermal plasma chemical vapor deposition for solar-cell application

The causes for the porosity of the microcrystalline material deposited by the expanding thermal plasma (ETP) chemical vapor deposition (CVD) technique have been investigated through IR-absorption measurements. The role of impinging ions on the structure of the material is discussed in relation to the hydrogen bounding configuration (microcrystalline factor). The ion energy is controlled through external RF biasing. Correlation between biasing and reduction of porosity is presented. The influence of high deposition pressure is as well studied, related with changes in a-Si structure

Manipulating the hydrogen-bonding configuration in ETP-CVD a-Si: H

The effect of ion bombardment on the relationship between the critical hydrogen concentration ccrit and the reactor pressure has been investigated for hydrogenated amorphous silicon (a-Si:H) deposited with the expanding thermal plasma-CVD (ETP-CVD) method. By increasing the reactor pressure, in particular above 0.24 mbar, the ionic cluster formation in the plasma can be increased, resulting in a decrease of ccrit. It is observed that this decrease of ccrit with increasing reactor pressure can not be compensated by ion bombardment at 14V biasing. Biasing with 20V however increases ccrit nearly up to the value obtained at low pressures. This observation indicates that the incorporation of ionic clusters formed at elevated reactor pressures can be reduced by substrate biasing, possibly due to break-up upon impact on the substrate surface or due to processes occurring in the secondary plasma close to the substrate. The onset of void formation in the film is found to depend on reactor pressure and substrate biasing, indicating that the maximum hydrogen solubility for ETP material might be affected by these deposition parameters

Polymeric amorphous carbon as p-type window within amorphous silicon solar cells

Amorphous carbon (a-C) has been shown to be intrinsically p-type, and polymeric a-C (PAC) possesses a wide Tauc band gap of 2.6 eV. We have replaced the p-type amorphous silicon carbide layer of a standard amorphous silicon solar cell with an intrinsic ultrathin layer of PAC. The thickness of the p layer had to be reduced from 9 to 2.5 nm in order to ensure sufficient conduction through the PAC film. Although the resulting external parameters suggest a decrease in the device efficiency from 9.2% to 3.8% due to a reduced value of open-circuit voltage, the spectral response shows an improvement in the 400–500-nm wavelength range, as a consequence of the wider band gap of the PAC layer.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc

New insights in microcrystalline silicon deposition with expanding thermal plasma chemical vapor deposition

We report on further insights in the microcrystalline silicon (µc-Si:H) deposition using expanding thermal plasma chemical vapor deposition. We have shown before that the refractive index at 2 eV of µc-Si:H layers increased if the silane (SiH4) was injected close to the substrate, while the deposition rate remained the same. We argued that at high injection-ring position, the SiH4 travels a long way to the substrate and therefore has a long interaction time with the plasma, in particular atomic hydrogen. In this way, the SiH4 injection position influences the number of hydrogen atoms stripped from the SiH4 as well as the consumption of atomic hydrogen. In this paper, we present an analysis of the growth flux of depositing particles as function of the radical production rate. The data suggest that there is no dependence on the SiH4 injection position, implying that the mix of depositing radicals is not changed. However, the data also show the microcrystalline-to-amorphous transition shifts to higher SiH4 flows for lower injection positions. We therefore now think that it is not the interaction time between the SiH4 and the arc plasma determining the material properties, but the interaction of excess atomic hydrogen with the µc-Si:H growth surface

A method for texturing a glass surface

The present invention relates to a new method of texturing a glass surface. In further aspects, the present invention relates to the resulting textured glass surface; to a photovoltaic device comprising the textured glass surface; and, to use of the textured glass surface for scattering light.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc

Effect of buffer layers on p-i-n a-Si:H solar cells deposited at high rate utilising an expanding thermal plasma

With a cascaded arc expanding thermal plasma intrinsic amorphous silicon can be deposited at growth rates varying from 0.2 to 10 nm/s. With increasing growth rate good material is obtained at higher deposition temperatures. At higher deposition temperatures the p-layer is deteriorated when the cell is deposited in a p-i-n sequence. A buffer layer can be used as a 'soft start' for the ETP layer and as protection of the p-layer from high deposition temperatures. In this paper we will discuss the effect on p-i-n solar cells when a buffer layer is incorporated