The Investagation Of Al-BSF Passivation Quality

In the forecast of international energy framework, coal all over the world will be exhausted in 220 year and oil will be exhausted in 30—60 year with the exploitation peak in 2012. Solar energy is invariable in 10 billion years. According to the forecast, solar energy will take a 20% share in the whole energy consumption in 2050 and increase to 70% share in 2100. Apparently, the energy framework will be changed at all in this century and solar energy will become the primary source of energy.In order to increase the cost-effective, there is a strong trend to reduce the wafer thickness. So the back surface recombination velocity S b begins to strongly influence solar cell performance when the ratio of minority carrier diffusion length to device thickness approached or exceeds unity. To improve the surface passivation quality and decrease S b have become more important. The screen-printed Al-back surface field (Al-BSF) is widely used now to reduce the back surface recombination velocity ( S b) and improve the efficiency of silicon solar cells. This paper is to investigate the Al-BSF passivation quality.Primary work and innovations of this thesis include: 1. According to the relationship between S b and the effective lifetimeτe, we calculated the S b byτe which was measured by WT2000. The lower of S b, the better of Al-BSF. For the calculating, we designed a special structure to investigate Al-BSF passivation quality. It was to prepare Al-BSF on both front and back surface, respectively. We also compared our result with the result of IQE measurement. Both the two results were match quite well in lone-wave length, which validates the feasibility of the new method.2. We also did some other experiments as assistance.. For example: we investigated the stability of WT2000 with error±2﹪. And, we tried different Al pastes and firing conditions. The result was that B paste could get the best efficiency at a peak firing temperature of 865℃, it indicated the best electronic performance and best passivation qulity of BSF. The method we introduced to calculate the surface recombination velocity is more direct and efficitive, comparing with IQE. And it can be used together with IQE method, as a reference each other.