Thin film silicon modules on plastic superstrates

Abstract

The aim of this research is to fabricate high efficiency a-Si/μc-Si tandem solar cell modules on flexible (polymer) superstrates using the Helianthos concept. As a first step we began by depositing the top cell which contains an amorphous silicon (a-Si:H) i-layer of ∼350nm made by VHF PECVD at 50MHz in a high vacuum multichamber system called ASTER, with hydrogen to silane gas flow ratio of 1:1. Such amorphous cells on-foil showed an initial active area (0.912cm2) efficiency of 7.69% (Voc=0.834V, FF=0.71). These cells were light soaked with white light at a controlled temperature of 50°C. The efficiency degradation was predominantly due to degradation of FF that amounted to only 11% after 1000h of light soaking. The cell-on-foil data prove that thin film silicon modules of high stability on cheap plastics can be made at a reasonable efficiency within 30min of deposition time. A minimodule of 8×7.5cm2 area (consisting of 8 cells interconnected in series) with the same single junction a-Si:H p–i–n structure had an initial efficiency of 6.7% (Voc=6.32V, FF=0.65).