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In this work, we present a technology for a high precision nanostructure replication process based on ultraviolet nanoimprint lithography for the application in the field of thin-film photovoltaics. The potential of the technology is demonstrated by the fabrication of microcrystalline silicon thin-film prototype solar cells. The high accuracy replication of random microstructures made from sputtered and etched ZnO:Al, used to scatter the incident light in thin solar cells, is shown by local topography investigations of the same 7.5 × 7.5 µm2 area on the master and the replica. Different types of imprint resists and imprint moulds were investigated to find the optimal, high precision replication technology. Two types of thin-film silicon solar cells, in p-i-n and n-i-p configuration, were fabricated to study the potential of the imprint technology for different applications. It is shown that solar cells deposited on an imprinted glass hold similar performances compared with reference solar cells fabricated with a standard process on textured ZnO:Al. Thus, it is demonstrated that the replication of light scattering structures by using an imprint process is an attractive method to decouple the scattering properties from the layer forming the electrical front contact. Because a simple and cheap high throughput process is used, this study additionally proves the relevance for the industrial mass production in the field of photovoltaics. Copyright © 2013 John Wiley & Sons, Ltd.

Hydrogenated amorphous silicon (a-Si:H) is conventionally deposited using static plasma-enhanced chemical vapor deposition (PECVD) processes. In this work, a very high frequency (VHF) dynamic deposition technique is presented, on the basis of linear plasma sources. This configuration deploys a simple reactor design and enables continuous deposition processes, leading to a high throughput. Hence, this technique may facilitate the use of flexible substrates. As a result, the production costs of thin-film silicon solar cells could be reduced significantly. We found a suitable regime for the homogeneous deposition of a-Si:H layers for growth rates from 0.35–1.1 nm/s. The single layer properties as well as the performance of corresponding a-Si:H solar cells are investigated and compared with a state-of-the-art radio frequency (RF) PECVD regime. By analyzing the Fourier transform infrared spectroscopy spectra of single layers, we found an increasing hydrogen concentration with deposition rate for both techniques, which is in agreement with earlier findings. At a given growth rate, the hydrogen concentration was at the same level for intrinsic layers deposited by RF-PECVD and VHF-PECVD. The initial efficiency of the corresponding p–i–n solar cells ranged from 9.6% at a deposition rate of 0.2 nm/s (RF regime) to 8.9% at 1.1 nm/s (VHF regime). After degradation, the solar cell efficiency stabilized between 7.8% and 5.9%, respectively. The solar cells incorporating intrinsic layers grown dynamically using the linear plasma sources and very high frequencies showed a higher stabilized efficiency and lower degradation loss than solar cells with intrinsic layers grown statically by RF-PECVD at the same deposition rate. Copyright © 2012 John Wiley & Sons, Ltd.

Silicon based thin tandem solar cells were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a 30 × 30 cm2 reactor. The layer thicknesses of the amorphous top cells and the microcrystalline bottom cells were significantly reduced compared to standard tandem cells that are optimized for high efficiency (typically with a total absorber layer thickness from 1.5 to 3 µm). The individual absorber layer thicknesses of the top and bottom cells were chosen so that the generated current densities are similar to each other. With such thin cells, having a total absorber layer thickness varying from 0.5 to 1.5 µm, initial efficiencies of 8.6–10.7% were achieved. The effects of thickness variations of both absorber layers on the device properties have been separately investigated. With the help of quantum efficiency (QE) measurements, we could demonstrate that by reducing the bottom cell thickness the top cell current density increased which is addressed to back-reflected light. Due to a very thin a-Si:H top cell, the thin tandem cells show a much lower degradation rate under continuous illumination at open circuit conditions compared to standard tandem and a-Si:H single junction cells. We demonstrate that thin tandem cells of around 550 nm show better stabilized efficiencies than a-Si:H and µc-Si:H single junction cells of comparable thickness. The results show the high potential of thin a-Si/µc-Si tandem cells for cost-effective photovoltaics. Copyright © 2010 John Wiley & Sons, Ltd.