Dry-epitaxial lift-off, integration, interconnect and encapsulation of foldable/rollable high efficiency solar cell modules

Abstract

OptiCOMP Networks is developing a new method for manufacturing thin, lightweight, flexible, portable high efficiency III-V PV modules that can be folded and rolled for space and terrestrial applications. Multi-junction inverted (IMM3J) and non-inverted cells are lifted off the Ge or GaAs growth wafer and transferred to inexpensive flexible polyimide permanent carrier substrate. The lift-off happens in fraction of a second. OptiCOMP uses proprietary materials and bonding techniques. No expensive ion implantation or slow chemical etching of a sacrificial layer is needed. Several cells are integrated on a common blanket polymeric sheet and interconnected by soldering copper ribbons. Both sides of the epi-layer can be contacted from the top side of the wafer. This eliminates the need for copper cladded polymeric substrates and reduces weight. The cells were fully encapsulated using transparent spray-on polyimide layer which replaces the cover glass. The thickness and CTE of the blanket polyimide layer were chosen to stress-balance the structure so that it remains flat in spite of 300°C temperature variations in orbit. The entire solar cell structure is less than 250 μm thick and achieves a specific power ratio of 340 W/kg. The base wafer is reused to grow another epi-layer and the cycle repeated. The cost of substrate materials is about 40% of the cost of the finished cell. OptiCOMP's process will result in savings in raw materials up to 30% of the cost of the cell and will enable terrestrial applications.