| Summary: | 碩士 === 明道大學 === 材料科學與工程學系碩士班 === 99 === Photovoltaic industrials have already attracted worldwide attention. Single crystalline solar cells play most important roles due to their high conversion efficiency especially passivated-emitter rear locally diffused (PERL) cells fabricated at university of New South Wales in Australia. In this study lots of parameters that influenced the devices performances were analyzed by Technology Computer Aided Design (TCAD) especially the different materials of back passivation layers (SiO2, Al2O3) and different ratios of rear diffused areas to whole device areas.
Some physical models including Shockley-Read-Hall and Auger recombination mechanisms model, concentration dependant lifetimes and low field mobility model that could solve the Poisson, the continuity, and the current density equations were used. We set some parameters of Al2O3 such as energy band gap, refractive index (N), extinction coefficient (K), electron affinity, and dielectric constant replacing those of SiO2 for investigating the variation of performances. It was found that devices with Al2O3 performed better especially in short-circuit current density (Jsc) and fill factor (FF). The characteristic of charge carriers effect for Al2O3 successfully reduced the recombination at the interface of c-Si and metal, and shielded minority carriers back to p-n junction. Furthermore, in order to research the influence of the rear locally diffused ranges on cell’s performance, we tried to vary the ratios of rear diffused areas to whole device areas containing 10%, 8%, 6%, 4%, 2%, 0.5%, respectively. From the result J-V curve, it was obtained that as the ratio decreased, open-circuit voltage (Voc) and Jsc almost maintained a constant, and the FF increased gradually. And the optimum efficiency reached 21.51%. In real process, the sizes of rear locally diffused areas fabricated by laser technology or lithography process technology are restricted to reduce endlessly. Generally the performances of PERL devices get better as the size of areas reduces.
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