Properties of n-type polycrystalline silicon solar cells formed by aluminium induced crystallization and CVD thickening

Abstract

Large-grained, n(+)n-type polycrystalline silicon (poly-Si) films were obtained on alumina substrates by combining the aluminium induced crystallization (AlC) process of amorphous silicon and chemical vapour deposition (LPCVD) at high temperature (1000 degrees C) for the epitaxial thickening. The n(+) seed layer was obtained by phosphorus doping of the AlC layer. The electron backscattering diffraction (EBSD) technique was used for the crystallographic analysis of the poly-Si thin films. Seed layers with an average grain size of 7.6 mu m were obtained on alumina substrates by exchange annealing at 475 degrees C for 6 h. Heterojunction emitter (HJE) solar cells were fabricated on such layers and their characteristics were monitored. IQE measurements show that n-type material based solar cells led to a much higher current collection over a large part of the spectrum compared to p-type cells. Accordingly a high effective diffusion length of about 2 mu m for n-type heterojunction solar cells was obtained while it is about 0.9 mu m for the p-type cell. As a result, the first n-type solar cells showed efficiencies above 5%, which is a very promising result considering that no optimization nor texturing have been applied so far. (C) 2010 Elsevier B.V. All rights reserved.