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

摘要

Damage-free reactive ion etch processes havebeen developed that allow the formation of grooves withintentional under-etching of the mask, e.g. photo resist. In asucceeding metal evaporation step this very same maskobstructs the deposition of metal such that the metal is onlydeposited on the bottom of the groove. In a lift-off process thesurplus metal is removed from the wafer surface. Thismetallization technique allows simple fabrication of single-sidecontacted solar cells. It has been used to form a buried basecontact through the homogeneous emitter of a rear contactsolar cell. Only one mask was used to define emitter and baseareas and to contact the base. After depositing the metal onthe bottom of the groove, it was electroplated. No significantshunts, i.e. no short circuits between emitter and base, areobserved even though during electroplating the metal hasgrown out of the grooves. This rear contact solar cell withburied-base contacts achieves an efficiency of 16.3% underfront side illumination (neither n++ nor p++ doping under thecontact fingers). The cell still lacks open-circuit voltage(595mV) and fill factor (70.9%), probably due to the lack ofside-wall passivation in the grooves and of a sealing of the open pn-junction.