Development of micromorph tandem solar cells on foil deposited by VHF-PECVD

Abstract

Micromorph silicon tandem solar cells on Asahi U-type SnO 2:F coated glass substrates have been fabricated by very high frequency plasma enhanced chemical vapour deposition (VHF-PECVD) in an ultra high vacuum multichamber system called ASTER. The hydrogenated microcrystalline silicon (μc-Si:H) intrinsic layer (i-layer) was deposited using a capacitively coupled reactor with a shower head cathode at high pressure depletion (HPD) conditions. We made bottom cell current limited tandem cells on Asahi U-type substrates, and they showed an initial efficiency of 10.2% ( V oc = 1.34 V, FF = 0.69). To develop the fabrication process of such tandem cells as flexible solar cells, we began as a first step the deposition of hydrogenated amorphous silicon (a-Si:H) p-i-n single junction cells on aluminium foil (provide by Helianthos b.v.) which was then transferred to plastic substrate at Helianthos b.v. Such a-Si:H cells showed an initial active area efficiency of 7.69% ( V oc = 0.834 V, FF = 0.70) and FF degraded by only 11% after 1000 h of light soaking, showing a high stability of these single junction cells. A minimodule (consisting of 8 cells) on foil delivered an initial aperture area efficiency of 6.7% ( V oc = 6.32 V, FF = 0.65).