Self-aligned metallization and reactive ion etched buried base contact solar cells

Damage-free reactive ion etch processes hare been developed that allow the formation of grooves with intentional under-etching of the mask, e.g. photo resist. In a succeeding metal evaporation step this very same mask obstruc ts the deposition of metal such that the metal is only deposited on the bot tom of the groove. In a lift-off process the surplus metal is removed from the wafer surface. This metallization technique allows simple fabrication o f single-side contacted solar cells. It has been used to form a buried base contact through the homogeneous emitter of a ram contact solar cell. Only one mask was used to define emitter and base areas and to contact the base. After depositing the metal on the bottom of the groove, it was electroplat ed. No significant shunts, i.e. no short circuits between emitter and base, are observed even though during electroplating the metal has gr own out of the grooves. This rear contact solar cell with buried-base contacts achiev es an efficiency of 16.3% under front side illumination (neither n(++) nor p(++) doping under the contact fingers). The cell still lacks open-circuit voltage (595 mV) and fill factor (70.9%), probably due to the lack of side- wall passivation in the grooves and of a sealing of the open pn-junction. C opyright (C) 1999 John Wiley & Sons, Ltd.