6″ crystalline silicon solar cell with electron-beam melting-based metallurgical route

Abstract

This paper presents a metallurgical route that consumes much less energy than the gasification route such as Siemens process-based photovoltaic (PV) value chain including metallurgical-grade silicon (MG-Si), solar-grade silicon (SoG-Si) purified by the metallurgical route, Czochralski (Cz) ingot growth, 6″ wafer fabrication, solar cell fabrication, and PV performance evaluation. Mono-like crystalline silicon ingot for achieving high purity was continuously cast with MG-Si for the fabrication of feedstock for Cz ingot growth through the advanced electron beam melting (EBM) system. The system was developed with the combination of vacuum refining part and directional solidification (DS) part for the purification of large amounts of MG-Si, where the two parts are connected by an overflow of Si melts to undergo continuous refining and casting processes in a chamber. To grow the mono-like crystalline Si ingot in our EBM system, a single crystalline seed was placed on the graphite dummy cylinder with DS zone. The mono-like crystalline Si ingot with high purity of >99.999% (above 5N) was blended 50–50 with undoped SoG-Si chunk for the compensation of boron dopant concentration in a crucible of Cz grower. The 156×156mm2 wafers were cut from Cz ingot grown with purity of >99.99999% (above 7N) by slurry-based multi-wire sawing and were fabricated by the conventional solar cell process. The measured photovoltaic performance recorded cell efficiency of 17.1%; hence its higher potential for application to the PV industry.