23% rear side poly-Si/SiO2 passivated silicon solar cell with optimized ion-implanted boron emitter and screen-printed contacts

We report on the understanding and optimization of ion-implanted boron emitters in combination with screen-printed contacts to produce very low recombination current density and high-efficiency cells with rear poly-Si/SiO2 passivated contact. Due to high bulk lifetime in n-base Si and very low recombination in the rear-side n+ passivated contact, recombination in the emitter limits the efficiency potential of manufacturable single-side passivated contact cells. Emitter recombination is governed by recombination under metal contacts (J0e,metal) and in the passivated regions in between (J0e,pass). Emitter profile engineering and dielectric passivation can lower the J0e,pass while paste chemistry and firing conditions can reduce J0e,metal by altering the extent of screen-printing induced emitter surface etching and the percentage of unetched dielectric islands under the metal contacts. We optimized implanted boron profiles, surface concentration and passivation, and junction depth in the sheet resistance range of 48-200 Ω/□ and achieved very low J0e,pass ( 140 Ω/□.•Recombination under metal contact is reduced by less surface etching and more unetched area under metal contacts.•Optimum boron sheet resistance is from 120–170 Ω/□ with rear poly-Si/SiO2 passivated contact by device modeling.•Simulated results were validated by fabricating fully screen-printed ~22.9% efficient bifacial n-TOPCon cells.