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Waste heat is a free and abundant energy source, with 15% of global total energy use existing as waste heat above 600 K. For 600–900 K temperature range, near-field thermophotovoltaics (NFTPVs) are theorized to be the most effective technology to recycle waste heat into electrical power. However, to date, experimental efficiencies have not exceeded 1.5%. In this work, we optimize the efficiency of three modeled InAs/InAsSbP-based room-temperature NFTPV devices positioned 0.1 μm from a 750 K p-doped Si radiator. We couple a one-dimensional fluctuational electrodynamics model for the near field optics to a two-dimensional drift-diffusion model, which we validated by reproducing measured dark current–voltage curves of two previously published InAs and InAsSbP devices. The optimized devices show four to six times higher above-bandgap energy transfer compared to the blackbody radiative limit, yielding enhanced power density, while simultaneously lowering parasitic sub-bandgap energy transfer by factors of 0.68–0.85. Substituting InAs front- and back-surface field layers with InAsSbP show 1.5- and 1.4-times higher efficiency and power output, respectively, from lowered parasitic diffusion currents. Of our three optimized designs, the best performing device has a double heterostructure with an n–i–p doping order from front to back. For radiator-thermophotovoltaic gaps of 0.01–10 μm and radiators within 600–900 K, this device has a maximum efficiency of 14.2% and a maximum power output of 1.55 W/cm2, both at 900 K. Within 600–900 K, the efficiency is always higher with near- vs far-field illumination; we calculate up to 3.7- and 107-times higher efficiency and power output, respectively, using near-field heat transfer.

We present a scheme for achieving thermal bistability based on the selective coupling of three optical resonances. This approach requires one of the resonant frequencies to be temperature dependent, which can occur in materials exhibiting strong thermo-optic effects. For illustration, we explore thermal bistability in two different passive systems, involving either a periodic array of Si ring resonators or parallel GaAs thin films separated by vacuum and exchanging heat in the near field. Such a scheme could prove useful for thermal memory devices operating with transition times $\lesssim$ hundreds of milliseconds.

We study thermal radiation from nonlinear ($\chi^{(3)}$) photonic cavities coupled to external channels and subject to incident monochromatic light. Our work extends related work on nonlinear mechanical oscillators [Phys. Rev. Lett. 97, 110602 (2006)] to the problem of thermal radiation, demonstrating that bistability can enhance thermal radiation by orders of magnitude and result in strong lineshape alternations, including "super-narrow spectral peaks" occurring at the onset of kinetic phase transitions. We show that when the cavities are designed so as to have perfect linear absorptivity (rate matching), such thermally activated transitions can be exploited to dramatically tune the output power and radiative properties of the cavity, leading to a kind of Kerr-mediated thermo-optic effect. Finally, we demonstrate that in certain parameter regimes, the output radiation exhibits Stokes and anti-Stokes side peaks whose relative magnitudes can be altered by tuning the internal temperature of the cavity relative to its surroundings, a consequence of strong correlations and interference between the emitted and reflected radiation.

We demonstrate actuation of a silicon photonic crystal membrane with a repulsive optical gradient force. The extent of the static actuation is extracted by examining the optical bistability as a combination of the optomechanical, thermo-optic, and photo-thermo-mechanical effects using coupled-mode theory. Device behavior is dominated by a repulsive optical force which results in displacements of ≈ 1 nm/mW. By employing an extended guided resonance which effectively eliminates multi-photon thermal and electronic nonlinearities, our silicon-based device provides a simple, non-intrusive solution to extending the actuation range of micro-electromechanical devices., United States. Defense Advanced Research Projects Agency. (Contract N66001-09-1-2070-DOD)

We propose an optomechanical structure consisting of a photonic-crystal (holey) membrane suspended above a layered silicon-on-insulator substrate in which resonant bonding/antibonding optical forces created by externally incident light from above enable all-optical control and actuation of stiction effects induced by the Casimir force. In this way, one can control how the Casimir force is expressed in the mechanical dynamics of the membrane, not by changing the Casimir force directly but by optically modifying the geometry and counteracting the mechanical spring constant to bring the system in or out of regimes where Casimir physics dominate. The same optical response (reflection spectrum) of the membrane to the incident light can be exploited to accurately measure the effects of the Casimir force on the equilibrium separation of the membrane.

Efficient charge transport is demonstrated in TiO2/PbS quantum dot solar cells where the PbS absorber (∼1.1 eV band gap) is deposited by dip coating and ethanedithiol ligand exchange, with power efficiencies above 3% at AM1.5. An increase in power efficiency occurs as the device temperature is lowered to 170 K, with a open-circuit voltage of 0.66 V, short-circuit current density of 28.6 mA/cm2 and fill factor of 42.4%. This remarkable temperature dependence is due to a large increase in charge transport between the PbS quantum dots with decreasing temperature.

We have fabricated ultrathin photovoltaic cadmium telluride (CdTe) film solar cells from colloidal nanorod solutions with a power conversion efficiency of 5.0% and internal quantum efficiency approaching unity near the band edge. Sintering of the CdTe nanorod films was necessary to facilitate grain growth and enhanced optical absorption. By analyzing electrode dependence, capacitance-voltage, temperature dependence, and current-voltage characteristics, the device performance is shown to be dominated by the formation of a p-CdTe/Al Schottky junction. The reduced need for material and cheaper processing make this an attractive technology for solar power generation.