Integrated Multi-Color Light Emitting Device Made With Hybrid Crystal Structure

III-nitride devices are commonly made on sapphire substrates today for various commercial electronic and optoelectronic applications. Thus, this innovation relates directly to the combination of devices on opposite sides of the sapphire substrate. One possible device combination is to have LEDs one side and solar cells on the other, such as for displays.

NASA researchers have developed the PAPA technology to increase the efficiency of the thin-film solar array assembly process, significantly decreasing assembly time and labor costs associated with manufacturing large scale solar arrays. Traditional solar cell assembly is a labor intensive, multi-step, time-consuming process. This manual assembly will not be possible in a space environment. To enable solar array assembly in space, PAPA leverages robotic automation to distill the traditional assembly method into four fully automated steps: applying adhesive to block substrate, placing the solar cells using a vacuum tool attached to a universal robotic arm, printing the interconnects and buses to connect the cells, and applying a protective cover. The PAPA technology is compatible with a variety of thin-film solar cells, including 3D printed cells (essential for future in-space manufacturing of arrays) and terrestrial manufacturing methods. As solar cell technologies mature, PAPA will be able to incorporate advancements into the paneling process. NASA researchers have begun to employ PAPA solar array fabrication and estimate savings of $300-$400/watt. For extraterrestrial assembly of solar panels the size of a football field or larger, PAPA could result in savings of approximately $500 million; a substantial cost savings driven by standardization and efficiency in the solar array assembly process. By demonstrating increases in assembly efficiency, time and cost savings, and passing multiple environmental exposure tests, the PAPA lab protype has completed the final phases of technology development and is ready for scale-up and commercialization.

This NASA Glenn innovation is a novel multi-junction photovoltaic cell constructed using selenium as a bonding material sandwiched between a thin film multi-junction wafer and a silicon substrate wafer, enabling higher efficiencies. A multi-junction photovoltaic cell differs from a single junction cell in that it has multiple sub-cells (p-n junctions) and can convert more of the sun's energy into electricity as the light passes through each layer. To further improve the efficiencies, this cell has three junctions, where the top wafer is made from high solar energy absorbing materials that form a two-junction cell made from the III-V semiconductor family, and the bottom substrate remains as a simple silicon wafer. The selenium interlayer is applied between the top and bottom wafers, then pressure annealed at 221°C (the melting temperature of selenium), then cooled. The selenium interlayer acts as a connective layer between the top cell that absorbs the short-wavelength light and the bottom silicon-based cell that absorbs the longer wavelengths. The three-junction solar cell manufactured using selenium as the transparent interlayer has a higher efficiency, converting more than twice the energy into electricity than traditional cells. To obtain even higher efficiencies of over 40%, both the top and bottom layers can be multi-junction solar cells with the selenium layer sandwiched in between. The resultant high performance multi-junction photovoltaic cell with the selenium interlayer provides more power per unit area while utilizing a low-cost silicon-based substrate. This unprecedented combination of increased efficiency and cost savings has considerable commercial potential. This is an early-stage technology requiring additional development. Glenn welcomes co-development opportunities.

Several of the patented methods included in this suite of technologies enable super-hetero-epitaxy of rhombohedral/cubic compound semiconductors on specially oriented trigonal (e.g. sapphire) or hexagonal (e.g. quartz) crystal wafer substrates. This includes alignment of the growth crystal lattice with the underlying substrate lattice to minimize misfit strain-induced dislocation defects in the growing crystal. Thus thicker, defect-free crystal layers can be made. Rhombohedral/Cubic crystal twin defects which is 60 degree rotated on [111] orientation in a rhombohedral/cubic SiGe layer structure can be reduced to well less than 1% by volume, essentially providing a defect-free semiconductor material. Alternately, engineered lattice structures with a high degree of twinning can provide SiGe with improved thermoelectric properties due to the phonon scattering that inhibits thermal conduction without compromising electrical conductivity. Additional patented technologies in this suite provide for physical vapor deposition (PVD) growth methods utilizing molten sputtering targets and thermal control of heated substrates, including electron beam heating, in order to give the atoms in the sputtered vapor or on the substrate surface the energy needed for the desired crystal growth. The remaining patented technologies enable x-ray diffraction methods for detecting and mapping crystal twin defects across the entire as-grown semiconductor layer. These defects are critical to the performance of any semiconductor device manufactured from such compound semiconductor materials.

Modeling additive manufacturing processes can be difficult due to the scale difference between the active processing point (e.g., a sub-millimeter melt pool) and the part itself. Typically, the tools used to model these processes are either too computationally intensive (due to high physical fidelity or inefficient computations) or are focused solely on either the microscale (e.g., microstructure) or macroscale (e.g., cracks). These pitfalls make the tools unsuitable for fast and efficient evaluations of additive manufacturing build files and parts. Failures in parts made by laser powder bed fusion (L-PBF) often come when there is a lack of fusion or overheating of the metal powder that causes areas of high porosity. AM-PM uses a point field-based method to model L-PBF process conditions from either the build instructions (pre-build) or in situ measurements (during the build). The AM-PM modeling technique has been tested in several builds including a Ti-6Al-4V test article that was divided into 16 parts, each with different build conditions. With AM-PM, calculations are performed faster than similar methods and the technique can be generalized to other additive manufacturing processes. The AM-PM method is at technology readiness level (TRL) 6 (system/subsystem model or prototype demonstration in a relevant environment) and is available for patent licensing.