Surface passivation of high efficiency silicon solar cells

Theoretically and experimentally determined design guides for significantly reduced recombination at the emitter and rear surfaces of full-area Al-BSF (back-surface region) and oxide-passivated bifacial cells are given. The impact of emitter thickness and surface dopant concentration on emitter saturation current and solar cell efficiency is outlined. A modified emitter structure (locally deep diffused below the metal contacts) is predicted to have superior performance. Measured V_oc values reveal the potential of deep emitter cells to achieve efficiencies above 20% in spite of high metallization factors. Experimentally, a strong dependence of passivation quality on oxide thickness and base doping concentration is found. The BSF quality of a diffused aluminium layer decreases strongly with increasing drive-in time. For SiO₂-passivated rear surfaces of bifacial cells, measurements of the dependence of the surface recombination velocity on the excess carrier concentration are presented