Characterization Of Electrical Properties On Crystal Silicon

Except for the impurity demand, the electrical property is one of the most important parameters for solar cell. As well known, the impurities and defects will affect the stability of electrical properties and the parameter of device. Silicon solar cells are divided into three types: single crystalline silicon solar cells, multi-crystalline silicon solar cells and amorphous silicon solar cells. Without the influence of grain boundary, the electrical properties of single crystalline silicon solar cells are much steady and the conversion efficiency is higher than multi-crystalline silicon solar cells. But high cost limits its application. For the multi-crystalline silicon films, although the cost is lower, it has a variety of defects, such as grain boundaries (GB), dislocation, micro-defects and impurities in materials (especially the transition-metal impurities); these are all the important factors impacting on the conversion efficiency of multi-crystalline solar cell Due to the diversity types of impurities and defects, the multi-crystalline silicon is lack of systematic research.So far, impurities and defects in electronic grade silicon material have been clear studied, influence of impurities and defects on the electrical properties in relatively low purity (4N-6N) of the silicon material is not clear. Therefore, study on defects and impurities in crystal silicon, and their influence on the electrical properties has great significance.In this paper, using the four point resistivity test system and WT-2000μ-PCD lifetime test machine to character the electrical properties of the single crystal silicon and the multicrystalline silicon. On the other hand, we evaluated the distribution of impurities and morphology of defects in crystalline silicon ingot by inductively coupled plasma emission spectrometry (ICP-MS), optical microscope, scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and other experimental methods. In the fifth chapter of the paper, we discussed the influence of heat treatment on the electrical properties.The conclusions as followed:(1) In single crystalline silicon, impurities and defects have a significant influence on the distribution of minority carrier lifetime. In the top part, less impurities and defects make the lifetime higher than other parts, about 0.674μs; the lifetime of middle part is lowest, about 0.368μs.the resistivity is too low to be used, about 0.05Ω·cm (2) The lifetime of the multi-crystalline silicon is 1.286μs,the resistivity is between 0.2 and 0.4Ω·cm. The electrical prosperity is relevant to grain boundaries, inclusions, impurities.(3) Results of heat treatment: (a) After the heat treatment of 200℃and 450℃, minority carrier lifetime and resistivity increased, uniformity is observed. (b) For the 800℃heat treatment of multi-crystalline and single crystalline silicon, the lifetime reach the highest when the time is 2h, because of the existence of high density of grain boundary and dislocation, the lifetime of multi-crystalline has larger margin of increase than single crystalline silicon (c) After the heat treatment 1150℃2h+800℃8h+1050℃8h,the single crystal has the highest lifetime, indicate that the best nucleated time is 8h;for the multi-crystalline silicon, the time is 16h.