Modelling on c-Si/a-Si:H wire solar cells: some key parameters to optimize the photovoltaic performance

I. Ngo, M.E. Gueunier-Farret^a, J. Alvarez and J.P. Kleider

LGEP, UMR 8507 CNRS, SUPELEC, UPMC, Université Paris-Sud 11, 11 rue Joliot-Curie, Plateau de Moulon, 91192 Gif-sur-Yvette Cedex, France

^a e-mail: farret@lgep.supelec.fr

Received: 21 November 2011
Accepted: 23 April 2012
Published online: 18 July 2012

Abstract

Solar cells based on silicon nano- or micro-wires have attracted much attention as a promising path for low cost photovoltaic technology. The key point of this structure is the decoupling of the light absorption from the carriers collection. In order to predict and optimize the performance potential of p- (or n-) doped c-Si/ n-(or p-) doped a-Si:H nanowire-based solar cells, we have used the Silvaco-Atlas software to model a single-wire device. In particular, we have noticed a drastic decrease of the open-circuit voltage (V_oc) when increasing the doping density of the silicon core beyond an optimum value. We present here a detailed study of the parameters that can alter the V_oc of c-Si(p)/a-Si:H (n) wires according to the doping density in c-Si. A comparison with simulation results obtained on planar c-Si/a-Si:H heterojunctions shows that the drop in V_oc, linked to an increase of the dark current in both structures, is more pronounced for radial junctions due to geometric criteria. These numerical modelling results have lead to a better understanding of transport phenomena within the wire.