Silicon solar cells with screen-printed front side metallization exceeding 19% efficiency
Thermal oxides are commonly used for the surface passivation of high-efficiency crystalline silicon solar cells and have led to the highest conversion efficiencies of mono- and multicrystalline silicon reported so far. In contrast to the laboratory fabrication of solar cell structures with lithographically defined and evaporated front contacts, in this study we combine several technologies ready for industrial implementation. On the front side, surface passivation of the lowly doped emitters up to 90 ?/sq is achieved with sputtered SiNx:H, the contact grid is created with screen-printing of a hotmelt silver paste, the electrical properties of the grid are improved by lightinduced silver plating. Since contact formation on the front requires a short high-temperature firing process, the rear surface passivation layer needs to be thermally stable. A wet thermal oxidation is applied on the rear and the surface recombination velocity of the fired oxide is experimentally determined to be below S <= 38 cm/s at the end of the process sequence. This includes evaporation of aluminium on the rear, the formation of laser-fired contacts and a short annealing process under air ambience. Monocrystalline solar cells were produced and 19.3% efficiency were obtained as best value on 4 cm2 cell area.