Si paste technology for high-efficiency solar cells

Abstract

This study demonstrates the successful implementation of industrially feasible local B doping as a local back surface field via the Si paste technology to fabricate high-efficiency solar cells. Si paste formed by 25wt% p-type Si nanoparticles and 75wt% organic solvent is used as the B source. Si paste is fully screen-printed on the preprocessed p-type Si rear surface, and then a homogenous Si cladding layer is formed by picosecond laser cladding. During this process, B diffuses into the Si substrate. The Si cladding layer itself is a heavily doped layer and forms a metallurgical bond between Si substrate. After co-firing with Al paste, cells obviously avoid Kirkendall void formation at contact regions. The heavily doped Si cladding layer and localized B doping can decrease the contact resistance and reduce the minority carrier recombination at the local metal contacts. This optimized rear surface design finally contributes to push the overall average cell efficiency over 20.3% on p-type CZ wafers.