p-doped μc-Si:H window layers prepared by hot-wire CVD for amorphous solar cell application

We report on boron-doped pc-Si:H films prepared by hot-wire chemical vapor deposition (HWCVD) using silane as a source gas and trimethylboron (TMB) as a dopant gas and their incorporation into all-HW amorphous silicon solar cells. The dark conductivity of these films was in the range of 1-10 (Omega cm)(-1). The open circuit voltage V-oc of the solar cells was found to decrease from 840 mV at low hydrogen dilution H-dil = 91 % to 770 mV at high H-dil = 97% during p-layer deposition which can be attributed to the increased crystallinity at higher H-dil and to subsequent band edge discontinuity between mu c-Si:H p- and amorphous i-layer. The short circuit current density J(sc) and the fill factor FF show an optimum at an intermediate H-dil and decrease for the highest H-dil. To improve the conversion efficiency and the reproducibility of the solar cells, an amorphous-like seed layer was incorporated between TCO and the bulk p-layer. The results obtained until now for amorphous solar cells with and without the seed layer are presented. The I-V parameters for the best p-i-n solar cell obtained so far are J(SC) = 13.95 mA/cm(2), V-OC = 834 mV, FF = 65% and eta = 7.6%, where the p-layers were prepared with 2% TMB. High open circuit voltages up to 847 mV could be achieved at higher TMB concentrations. (c) 2006 Elsevier B.V. All rights reserved.