| Description |
In recent years, n-type silicon is getting popular in the photovoltaic industry because of its advantages over p-type silicon. However, the solar cell industry has not been fully established for n-type solar cells. This is mainly due to the difficulties in emitter formation with p-type dopants, its passivation and contact formation with the existing industrial techniques. The commonly used liquid dopant BBr3 results in higher yield, but its hazardous nature increases the safety requirements and hence increases the cost of production associated with its diffusion. Other dopant sources, which are not hazardous have also been studied to lower the cost of fabrication of the emitter. Commercially available Boron spin on dopant (BSoD) is one of them and it yields uniform doping due to its diffusion. But, during the process of BSoD diffusion, the formation of boron-rich layer (BRL) is an unavoidable phenomenon. For performance analysis of a BSoD diffused solar cell, it is important to understand the impact of the BRL on different parameters of the device.
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n this work, different structural behaviours of a BRL with respect to process step conditions are discussed in terms of its morphology, optical and electrical properties. The characterization processes show that the BRL properties are dependent on its thickness and its Boron concentration. The carrier lifetime degradation is proportional to the BRL thicknesses. Controlled diffusion processes and different oxidation techniques used in this work can partially remove the BRL from the emitter surface and can improve the carrier lifetimes by more than 10%. But for thicknesses higher than 50 nm, the improvement is not seen. The observed Jsc and Voc values become zero for the BRL thicknesses higher than 40 nm and the recovery of the device is not possible with oxidation nor with HNA etching.
There are many issues associated with the BRL formed during the diffusion of BSoD source. The impact of the BRL is the main reason because of which BSoD is not that popular as BBr3 dopant.
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