Integration of Expanding Thermal Plasma deposited Hydrogenated Amorphous Silicon in Solar Cells

Abstract

A cascaded arc expanding thermal plasma is used to deposit intrinsic hydrogenated amorphous silicon at growth rates between 0.2 and 3 nm/s. Incorporation into a single junction p-i-n solar cell resulted in an initial efficiency of 6.7%, whereas all the optical and initial electrical properties of the individual layers are comparable with RF-PECVD deposited films. In this cell the intrinsic layer was deposited at 0.85 nm/s and at a deposition temperature of 250°C, which is the temperature limit for growing the p-i-n sequence. The cell efficiency is limited by the fill factor and using a buffer layer at the p-i interface deposited with RF-PECVD at low growth rate can increase this. The increase in fill factor is a result of a lower initial defect density near the p-i interface then obtained with the expanding thermal plasma, resulting in better charge carrier collection. To use larger growth rates, while maintaining the material properties, higher deposition temperatures are required. Higher deposition temperatures result in a smaller optical bandgap for the intrinsic layer and deterioration of the p-type layer, resulting in a lower opencircuit voltage. First results on applying a buffer layer will also be presented.

A path towards a better characterisation of silicon thin‐film solar cells: depth profile analysis by pulsed radiofrequency glow discharge optical emission spectrometry

“…Infrared absorption measurements between 2800 and 400 cm À1 wavenumbers obtained using a Fourier transform infrared Nicolet 6700 spectrometer (Thermo Scientific, Waltham, MA) in transmittance mode were performed under inert atmosphere. As can be seen in Figure 2, hydrogen contents achieved for the different laboratory standards were found to be in the range between 5% and 13% (atomic), these being values in agreement with those reported by Korevaar et al [24].…”

“…As can be seen in Figure , hydrogen contents achieved for the different laboratory standards were found to be in the range between 5% and 13% (atomic), these being values in agreement with those reported by Korevaar et al . .…”

High-rate a-Si:H and μc-Si:H Film Growth Studied by Advanced Plasma and in situ Film Diagnostics

“…The fact that low-defect density a-Si:H can be obtained by the ETP at deposition rates up to 100 Å/s has already been addressed extensively in previous publications [1]. At the moment, the efforts concerning a-Si:H are mainly focused on the integration of the material in solar cells [2]. A very important issue in this respect seems to be the relatively high substrate temperature (~400 ºC) that is required to obtain good quality a-Si:H at the highest rates.…”

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

“…The short-circuit current density decreases slightly from -15 mA/cm2 for a cell without a buffer layer to -14 mAlcm2 for a cell with a buffer layer of 50 nm (not shown). This decrease is expected [3,6] because the bandgap of the buffer layer is -0.07 eV larger than the bandgap of the ETP layer. The fill factor increases by more than 10% and the open-circuit voltage increases by almost 25% up to a value of -0.7 V. We believe that by improving the buffer layer properties it should be possible to obtain a V, of 0.75V.…”

“…Furthermore, it is found that the fill factor of cells with the intrinsic layer deposited with the ETP method is lower than that obtained with cells deposited completely with RF-PECVD. This difference is attributed to a larger defect density near the p-i interface for the ETP cell [6]. We will present results of solar cells in which a buffer layer deposited at 0.2 nm/s with RF-PECVD is applied on top of the player before intrinsic layer deposition.…”