High efficiency solar cells grown on spalled germanium without polishing

Implementing device removal and substrate reuse provides an opportunity for substrate cost reduction. Controlled spalling allows removal of devices; however, the fracture-based process generates surfaces with significant morphological changes compared to polished wafers. We create small single junction devices across full 2″ spalled germanium wafers without polishing before epitaxial growth. We identify device defects related to surface morphology and their impact on cell performance using physical and functional characterization techniques. A single junction efficiency above 23% and VOC of 1.01 V is achieved, demonstrating that spalled germanium does not need to be returned to a pristine, polished state to achieve high quality device performance.