Silicon bottom subcell fabrication, loss analysis and shunt identification for two-terminal multijunction solar cells

Abstract

Two-terminal multijunction solar cells are a promising technology to surpass the energy-conversion efficiency of commercial single junction devices. Multijunction solar cells that integrate silicon bottom subcells could allow cost-effective efficiency enhancements and further growth in the worldwide installed photovoltaic capacity. However, the fabrication and characterization of multijunction devices is more complex than the standard single junction case, due to optical, electrical and architecture constraints. In this context, this thesis proposes and tests methods for fabrication and characterization of two-terminal multijunction devices, with special emphasis in the bottom silicon subcells. A low-capex, local area back-surface field, silicon cell is adapted for operation in a two-terminal perovskite-silicon tandem device. A contactless voltage loss analysis methodology is developed, and used to optimize the tunnel junction of the device. Finally, a general methodology to identify the shunted cells in two-terminal tandem devices is developed and validated in GaAs/GaAs tandem device. These characterization methodologies allow an adequate diagnosis of quality issues in multijunction solar cells, and provide useful tools for future efficiency improvements.