This Small Business Innovation Research Phase I project will focus on development of novel optoelectronic nanomaterials with long photocarrier lifetimes, low recombination losses, and enhanced coupling to infrared (IR) radiation. The innovation which will enable this is the employment of quantum dots (QDs) with built-in charge to create specified three-dimensional potential profiles, where the areas of IR absorption (QDs, QD rows, and QD clusters) are separated from the conducting channels by potential barriers. The charging of dots is realized by selective doping of the interdot space. The resulting long photoelectron lifetime will increase the photoconductive gain and responsivity of sensors based on this innovation. This structure will also decrease the generation-recombination noise and improve the sensitivity of photodetectors. Low recombination losses and enhanced coupling to IR radiation will improve the photovoltaic efficiency of quantum dot solar cells. The Phase I research includes nanoscale design, development of growth and processing technologies, and comprehensive analyses of the test structures and prototype devices. By providing the needed fundamental and technological basis, this program will develop advanced nanomaterials with a number of optoelectronic applications.
The broader impact/commercial potential of this project will be development of novel optoelectronic nanomaterials, which will lead to potential breakthroughs in IR sensing and photovoltaics. With appropriate modifications, the technology is applicable to practically all QD materials and structures fabricated by any method. Optoelectronic nanomaterials that combine strong coupling to radiation with long and manageable photocarrier lifetime are crucial for the development of next generation IR sensors. Sensitive detectors operating at room temperature will significantly increase the commercial market of IR technologies, which have applications including industrial and environmental monitoring, chemical sensing, medical diagnostics, and detection of explosives. The high scalability of these structures provides a wide opportunity for imaging applications. When integrated into in p-i-n junctions for solar energy harvesting, these structures will provide an additional ~20% improvement in the conversion efficiency (allowing 45-50% total efficiency without concentrators). In the Phase I project, we will demonstrate that harvesting and conversion of IR radiation in this way adds at least an additional 7% to the total conversion efficiency. The potential high efficiency and relatively low cost (as compared with efficient multi-junction cells) make this technology commercially viable for various photovoltaic applications.
This Small Business Innovation Research (SBIR) Phase I project aims at the development of novel optoelectronic and photovoltaic nanomaterials with strong harvesting of infrared radiation, long photocarier lifetime, and enhanced photoresponse. The principal component of such nanomaterials is a medium which consists of quantum dots with built-in charge (Q-BIC). Charged quantum dots provide strong absorption of the infrared radiation and prevent trapping of photocarriers by dots. During Phase I R&D the technological route for growing Q-BIC media with controllable parameters was created and dozens of Q-BIC infrared photodetectors and photovoltaic devices were fabricated. After several design-growth-characterization cycles the technological processes, parameters of Q-BIC media, and the device designs were optimized to further suppress recombination processes via quantum dots. The complex characterization of Q-BIC media includes the structural characterization (scanning electron microscopy and transmission electron microscopy), spectral characterization (photoluminescence measurements), electrical characterization (dark- and photo- current-voltage measurements), and thermal characterization (temperature dependences of spectral and electrical parameters). The Phase I results demonstrate feasibility and strong potential of Q-BIC technology for advanced infrared sensing and high-efficiency, broadband photovoltaic conversion. The data obtained show that charging of quantum dots increases the responsivity of infrared photodetectors. This technology may successfully compete with quantum-well infrared photodetectors which are currently used in cooled multi-element focal plane arrays. The room temperature Q-BIC photodetectors may significantly increase both commercial and defense markets. Numerous applications include industrial and environmental monitoring, chemical sensing, medical diagnostics, and detection of explosives. Harvesting and conversion of infrared radiation by charged quantum dots placed in a single-junction solar cell substantially increase conversion efficiency of solar cells. The Q-BIC photovoltaic devices fabricated in this research show that the conversion of infrared radiation by charged quantum dots adds ~6% to absolute value of the efficiency. The Q-BIC technology is expected to compete successfully with the multi-junction solar cells. Potential high efficiency, relatively low cost (compared with the efficient multi-junction cells), and tolerance to the temperature variations make this technology marketable for concentrating photovoltaics. The methodology and principles developed during this research are universal and may lead to potential breakthroughs in infrared/terahertz sensing and photovoltaics. With corresponding modifications, the technology is applicable to practically all quantum-dot materials and structures, such as grown by molecular beam epitaxy quantum-dot structures, solvents of nanoparticles, nanomaterials obtained by solvent evaporation, etc.
