A comprehensive study for emitter formation, with spin-on dopant source, on solar grade silicon solar cells, suitable for ablated laser emitter contact formation

摘要

Low cost and high efficiency are the keys to reducing the cost of photovoltaic electricity. To realize high efficiency, the quality of emitter is critical. In this paper we report on the study of different emitter formation, fabricated on solar grade silicon, suitable for new solar cells manufacturing process. Laser ablation of a passivation layer is a key factor to preserve the quality of the emitter before the contact formation. Emitter formation is settled in order to produce lower cost high efficiency solar cells processed on large area using techniques scalable to industry. The work has been focused on the combination of different emitter formation. Starting from standard POCL3 emitter formation considered as reference, a spin-on dopant (SOD) with different phosphorous concentration has been used to obtain the most suitable configuration for the emitter in conjunction with a good front ohmic contact formation, using NI-Cu (ablating, by laser, a passivation layer) and back contact collection realized via laser fired contact. All the different diffused profiles has been analyzed and characterized to assure the right choice. Starting from phosphorous spin-on sources an appropriate doping profile, in an open tube, has been identified in such a way to have both: a good contac formation, realized via laser ablation of an antireflection coating and passivation layer realized on emitter side, and an effective light absorption. The obtained diffusion profile coupled with an antireflection and passivation layer, formed by a combination of silicon nitride and amorphous silicon at low temperature, has given a value of Voc over 620 mV.