A program that started at the beginning of the year and headed by Energy Research Centre of the Netherlands (ECN), hopes to develop a new amorphous and microcrystalline silicon thin film cell using plastics as the substrate foil. The three-year ‘Silicon-Light’ programme is subsidized by the European Commission in the framework of the thematic research programme Energy in FP7. The R&D consortium includes EPFL, University of Copenhagen, University of Valencia, JiaoTong University of Shanghai, Umicore and VHF Technologies (Flexcell), the hopeful commercial end-user of the programme. Flexcell is a subsidiary of Q-Cells.
To be able to use low-cost materials such as plastics, the Silicon-Light’ programme will develop low process temperatures (typically below 200ºC), using plasma enhanced chemical vapour deposition (PECVD) processes.
TCO (transparent conductive oxide) layers are needed to collect the generated current at the front side of the solar cell, however instead of using indium tin oxide (ITO) the team plan to evaluate whether zinc-oxide is a possible alternative. Zinc-oxide has certain disadvantages related to its stability in humid environments so the plan is to have new TCO materials that should combine the advantages of ITO with that of ZnO.
The consortium will also investigate methods to create light-scattering textures at the rear side of the cell. For the fabrication of these nanometre-scale textures, methods from the semiconductor industry like e-beam lithography will be applied. The e-beam lithography technology would use for developing the ‘master’ cell structures only. To demonstrate that these textures can be manufactured on large scale, these methods will be combined with large-scale production methods which are used in the holographic industry.
ECN Solar Energy’s project coordinator Wim Soppe told PV-Tech that the programme aims at conversion efficiencies of >11% (stable) at the cell level and >7.5% (stable) on modules of 60 x 30 cm2.
Soppe noted that the best produced cells on foil substrates so far obtained where achieved by project partner EPFL, having a stable efficiency of 9.8% (n-i-p cell).