Tandem and triple junction silicon thin film solar cells with intrinsic layers prepared by hot-wire CVD

Abstract

Hot-wire CVD (HWCVD) can be applied for the deposition of various types of silicon films. At Utrecht University intrinsic layers of high optoelectronic quality have been successfully used as the absorber layers in thin film solar cells. This paper presents results for a proto-Si/μc-Si cell and a proto-Si/μc-Si/μc-Si triple junction cell with its μc–μc middle-bottom tandem cell, all deposited in nip configuration onto plain stainless steel. The proto-Si/μc-Si tandem had a good V oc of 1.38 V and a high FF of 0.75. Its efficiency of 7.3% was, considering the absence of a back reflector, adequate. The μc–μc tandem cell had a good V oc of 1.04 V and a very high FF of 0.77. Since both tandem cells were current-limited by the bottom cell, the high FF-values indicate that our μc-Si material is of very high quality. The triple cell had a lower FF of 0.69 and its V oc of 1.77 V was lower than the sum of the middle–bottom tandem and the top cell. Filtered light-IV measurements on the μc–μc tandem cell indicated that the losses in FF and V oc observed for the triple cell are, at least partly, a result of the optical absorption by the proto-Si top cell.