Front Side Optimization on Boron- and Gallium-Doped Cz-Si PERC Solar Cells Exceeding 22% Conversion Efficiency

This work reviews on our industrial-oriented passivated emitter and rear cell (PERC) baseline process for Czochralski-grown silicon (Cz-Si) wafers at the Fraunhofer ISE PV-TEC pilot-line. We perform several front side optimizations based on homogeneous emitter doping: finger width reduction of the screen-printed silver fingers, improved silver paste, and implementation of low-temperature thermal oxidation. This yields peak energy conversion efficiencies of 22.1% for boron-doped Cz-Si from LONGi and 22.2% for gallium-doped Cz-Si from Fraunhofer CSP. We show that gallium-doped Cz-Si wafers offer an industrially feasible option to further improve PERC-type but also other solar cell concepts on p-type Cz-Si. We also demonstrate the possibility to omit regeneration procedures that are needed to suppress the boron-oxygen-related light-induced degradation effects as known for conventional borondoped Cz-Si.