In thermophotovoltaics, photovoltaic cells convert heat from a thermal emitter to electricity. One way to obtain high-efficiency devices is to tailor the emitted spectrum to a specific solar cell. Here, we propose to use ultra-thin films to tailor the emission of hot bodies, where we can control the emission spectrum through material choice and film thickness. We predict power conversion efficiencies >50%, and suggest new material systems for exploration with potential efficiencies >60%. Our concept is universal and can be expanded to other high-temperature photonic applications for spectral control of thermal emission.
KEYWORDS: Thin films, Solar cells, Coating, Temperature metrology, Thin film coatings, Solar energy, Silicon, Refractive index, Photonics, Optical properties
The field of thermophotovoltaics offers a direct method to translate the heat generated as a byproduct of other standard energy generation techniques into usable electricity. This requires an emitted spectrum tailored to produce the maximum possible amount of light in a wavelength regime which is utilizable by a given photovoltaic cell. In this work, we investigate the efficiency of coating/substrate emitters using ~50 materials with melting points >2000C. We show combinations including oxide/refractory metal coating/substrate pairs which result in an FOM of >40% at 1800C, demonstrating their potential to greatly outperform currently available thermophotovoltaic devices.
Low-cost, high-efficiency metal halide perovskite solar cells (PSC) are a promising alternative to Si photovoltaics, but poor stability currently precludes commercialization. We present a framework for accelerated PSC design using machine learning (ML) to identify optimal compositions, fabrication parameters, and device operating conditions. We present four examples showcasing our ML roadmap using various types of neural networks, applied to diverse problems such as forecasting time-series photoluminescence (PL) from perovskite thin films, projecting PSC power output and degradation over time, and predicting figures of merit from simple, high-throughput experimental procedures. Our paradigm informs the rational development of perovskite devices, providing an accelerated pathway to commercialization.
Traditional metal nanostructures and thin-films are the fundamental building blocks for photonic devices, yet they are intrinsically limited by the pre-defined dielectric function, i.e. permittivity. Alternatively, the permittivity of alloyed structures can be engineered by tuning their chemical compositions, which allows for customization of the optical responses. Here we present several alloy-based systems (including Ag-Au, Al-Cu, Pd-Au, among others) and demonstrate how their optical properties are tailored with varying chemical compositions. Examples of their applications in super-absorbing, hydrogen sensing and hot carrier devices are also introduced.
Semiconductor materials are well suited for power conversion when the incident photon energy is slightly larger than the bandgap energy of the semiconductor. However, for photons with energy significantly greater than the bandgap energy, power conversion efficiencies are low. Further, for photons with energy below the bandgap energy, the absence of absorption results in no power generation. Here, we describe photon detection and power conversion of both high- and low-energy photons using hot carrier effects. For the absorption of high-energy photons, excited electrons and holes have excess kinetic energy that is typically lost through thermalization processes between the carriers and the lattice. However, collection of hot carriers before thermalization allows for reduced power loss. Devices utilizing plasmonic nanostructures or simple three-layer stacks (transparent conductor–insulator–metal) can be used to generate and collect these hot carriers. Alternatively, hot carrier collection from sub-bandgap photons can be possible by forming a Schottky junction with an absorbing metal so that hot carriers generated in the metal can be injected across the semiconductor–metal interface. Such structures enable near-IR detection based on sub-bandgap photon absorption. Further, utilization and optimization of localized surface plasmon resonances can increase optical absorption and hot carrier generation (through plasmon decay). Combining these concepts, hot carrier generation and collection can be exploited over a large range of incident wavelengths spanning the UV, visible, and IR.
Semiconductor materials are well suited for power conversion when the incident photon energy is slightly larger than the bandgap energy of the semiconductor. However, for photons with energy significantly greater than the bandgap energy, power conversion efficiencies are low. Further, for photons with energy below the bandgap energy, the absence of absorption results in no power conversion. Here we describe photon detection and power conversion of both high energy and sub-bandgap photons using hot carrier effects. For the absorption of high-energy photons, excited electrons and holes have excess kinetic energy, which results in the generation of hot electrons and holes. Energy is typically lost through a thermalization process between the carriers and the lattice. However, collection of carriers before thermalization allows for reduced power loss. Devices consisting of a three-layer stack (transparent conductor – insulator – metal) can be used to generate and collect these hot carriers. Alternatively, when a semiconductor is used, photons with energy below the semiconductor bandgap energy generally do not generate electrons and holes; however, hot carrier collection is still possible in semiconductor devices with a metal layer when a Schottky junction is formed at the semiconductor-metal interface. Such structures enable IR detection based on sub-bandgap photon absorption. Combining these concepts, hot carrier generation and collection and be exploited over a large range of incident wavelengths spanning the UV, visible, and IR.
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