Effects of nanowire size and geometry on silicon nanowire array thin film solar cells

Abstract

Here, the authors demonstrate the fabrication of silicon nanowire array based solar cells consisting of crystalline Si cores and amorphous a-Si:H layers using a single pump-down plasma-enhanced chemical vapor deposition (PECVD) process. The authors investigate the influence of geometry, physical dimensions, and doping of the nanowire arrays on the solar cell performance. The authors show that the length and thickness of the nanowire radial NIP junction have a significant influence on the current density–voltage characteristics and external quantum efficiency of the cells. The efficiency of radial solar cells is found to be mainly driven by the photogenerated current which is the largest when the thickness of the absorber film is approximately one half of the NIP nanowire length. Doping of the nanowires done by adding phosphine gas in situ in the PECVD growth has affected both the axial and radial nanowire growth rate, leading to the nanowire growth reduction in both directions at higher doping concentrations. The mechanism of light absorption, the ratio of crystalline and amorphous Si phases, and bulk and interface electrical losses for varying nanowire dimensions and amorphous layer thicknesses in the solar cells are discussed.