Transfer printing of fully formed thin-film microscale GalnP/GaAs solar cell on silicon with interfacial material of HfO2

To bypass the requirements of epitaxial and current matching in monolithic stacks, we propose a promising strategy by releasing and transfer printing fully formed, thin-film microscale double-junction (2J) solar cells with band gaps of 1.9/1.37 eV onto Si substrates to demonstrate four-terminal triple junction architecture with band gaps of 1.9/137/1.1 eV. Meanwhile, the 20 nm-thick HfO2 film, based on numerical calculation, serves as an optically-transparent and electrically-insulating interface material. NIR optical images, together with cross sectional view SEM image and spatially-resolved reflectance confirm the interface bonding of high uniformity and quality. About 20% averaged reflection in the wavelength range of 900 nm-1100 nm, which falls in the absorption range of bottom silicon cell, is almost entirely introduced by the top 2J cell without antireflective coating (ARC). With perfect top ARC, simulated reflectance spectra, comparable to direct bonding case, has presented about 5% averaged over 900 nm-1250 nm, bringing bottom silicon similar to 15% boost of photon flux. (C) 2016 Elsevier Ltd. All rights reserved.