Thermophotovoltaic (TPV) cells utilize locally emitted thermal radiation to generate electricity. To reach high efficiencies, the unusable spectrum (the below bandgap, or out-of-band spectrum) of the thermal source must be recycled to the source. Current approaches for photon recycling use back-surface reflectors or front surface filters, however, these have not exceeded 95 % out-of-band reflectance. In this work, we demonstrate an out-of-band reflectance of ~99% in a thin-film In0.53Ga0.47As TPV using an air-bridge as photon reflector, which effectively eliminates out-of-band absorption losses. The nearly perfect photon utilization enables a record high TPV power conversion efficiency of over 31% measured with a 1500K blackbody emitter.
The retina employs a unique hemispherical architecture that provides a low-aberration image with wide field of view. However, owing to established optoelectronic fabrication technologies, conventional imagers are limited to a planar architecture. Despite that limitation, intensive endeavors have been made on mimicking the hemispherical detector geometry. The most critical limitation of the existing approaches is the increased spacing between adjacent detectors on deformation to form non-developable three-dimensional array surfaces. Here, we demonstrate retina-like imagers that do not suffer from pixel spacing enlargement upon transforming into the desired three-dimensional hemispherical shape. The approach employs fabrication processes that are generally employed for optoelectronics on planar flexible plastic foils followed by the unique elongation-free conformal deformation on an elastomeric transfer handle. Using these methods, we demonstrate hemispherical imagers with high optical performance, high yield, and, importantly, unchanged pixel density upon deformation and transformation from a developable two-dimensional to a non-developable three-dimensional surface. This approach is compatible with batch fabrication of imagers with many high performance crystalline materials including but not limited to Si, GaAs, InGaAs, and etc. The demonstrated methods provide a practical path of making high pixel density imaging system on non-developable surfaces.