Progress in the Industrial Evaluation of the mc-Si PERCT Technology Based on Boron Diffusion

In this paper, we present the recent progress of the evaluation of the multi Si PERCT technology in an industrial pilot production of the Chinese cell manufacturer Lu’an. Our technology is an alternative to the AlOx based PERC technology for improving multi-crystalline solar cell efficiencies above 18.5% and it is based on standard mass production equipment and wafer quality. An additional unique feature of this technology is the manufacture of bifacial multi-crystalline solar cells with screen-printed finger grid on the rear side instead of a full area Al-BSF.The PERCT cell architecture is based on a “passivated emitter rear totally diffused (PERT)” cell design for p-type wafers. The totally diffused BSF is realized by a cost effective and short BBr3 boron diffusion step in a standard diffusion tube furnace - prior to the back side passivation and protection by a PECVD SiNx.RCT's multi PERCT technology upgrade is currently evaluated in an industrial pilot line of a Chinese cell manufacturer. Using the equipment available on site, an average efficiency of 18.4% could be achieved (without front side optimization). Accordingly an efficiency gain of 0.52% absolute was demonstrated on standard multi-crystalline wafer material.A unique feature of the PERCT technology is the opportunity to prepare bifacial cells on multi-crystalline wafer material. The world's first bifacial multi-crystalline solar cell with a screen printed Al-grid and a front side efficiency of 18% was realized. Up to 15% cost savings can be achieved by using the bifacial multi PERCT technology.