Professional Education

  • Doctor of Philosophy, Georgia Institute of Technology (2016)

Stanford Advisors

All Publications

  • Self-sustaining thermophotonic circuits. Proceedings of the National Academy of Sciences of the United States of America Zhao, B., Buddhiraju, S., Santhanam, P., Chen, K., Fan, S. 2019


    Photons represent one of the most important heat carriers. The ability to convert photon heat flow to electricity is therefore of substantial importance for renewable energy applications. However, photon-based systems that convert heat to electricity, including thermophotovoltaic systems where photons are generated from passive thermal emitters, have long been limited by low power density. This limitation persists even with near-field enhancement techniques. Thermophotonic systems, which utilize active photon emitters such as light-emitting diodes, have the potential to significantly further enhance the power density. However, this potential has not been realized in practice, due in part to the fundamental difficulty in thermodynamics of designing a self-sustaining circuit that enables steady-state power generation. Here, we overcome such difficulty by introducing a configuration where the light-emitting diodes are connected in series, and thus multiple photons can be generated from a single injected electron. As a result we propose a self-sustaining thermophotonic circuit where the steady-state power density can exceed thermophotovoltaic systems by many orders of magnitude. This work points to possibilities for constructing heat engines with light as the working medium. The flexibility of controlling the relations between electron and photon flux, as we show in our design, may also be of general importance for optoelectronics-based energy technology.

    View details for DOI 10.1073/pnas.1904938116

    View details for PubMedID 31118287

  • Experimental demonstration of energy harvesting from the sky using the negative illumination effect of a semiconductor photodiode APPLIED PHYSICS LETTERS Ono, M., Santhanam, P., Li, W., Zhao, B., Fan, S. 2019; 114 (16)

    View details for DOI 10.1063/1.5089783

    View details for Web of Science ID 000466264600002

  • Gate-Tunable Near-Field Heat Transfer ACS PHOTONICS Papadakis, G. T., Zhao, B., Buddhiraju, S., Fan, S. 2019; 6 (3): 709–19
  • High Reflection from a One-Dimensional Array of Graphene Nanoribbons ACS PHOTONICS Zhao, N., Zhao, Z., Williamson, I. D., Boutami, S., Zhao, B., Fan, S. 2019; 6 (2): 339–44
  • MESH: A free electromagnetic solver for far-field and near-field radiative heat transfer for layered periodic structures COMPUTER PHYSICS COMMUNICATIONS Chen, K., Zhao, B., Fan, S. 2018; 231: 163–72
  • Near-Field Thermophotonic Systems for Low-Grade Waste-Heat Recovery NANO LETTERS Zhao, B., Santhanam, P., Chen, K., Buddhiraju, S., Fan, S. 2018; 18 (8): 5224–30


    Low-grade waste heat contains an enormous amount of exergy that can be recovered for renewable-energy generation. Current solid-state techniques for recovering low-grade waste heat, such as thermoelectric generators and thermophotovoltaics, however, are limited by low conversion efficiencies or power densities. In this work, we propose a solid-state near-field thermophotonic system. The system consists of a light-emitting diode (LED) on the hot side and a photovoltaic (PV) cell on the cold side. Part of the generated power by the PV cell is used to positively bias the LED. When operating in the near-field regime, the system can have power density and conversion efficiency significantly exceeding the performance of current solid-state approaches for low-grade waste-heat recovery. For example, when the gap spacing is 10 nm and the hot side and cold side are, respectively, 600 and 300 K, we show that the generated electric power density and thermal-to-electrical conversion efficiency can reach 9.6 W/cm2 and 9.8%, respectively, significantly outperforming the current record-setting thermoelectric generators. We identify the alignment of the band gaps of the LED and the PV cell, the appropriate choice of thickness of the LED and PV cell to mitigate the effect of non-radiative recombination, and the use of highly reflective back mirrors as key factors that affect the performance of the system. Our work points to the significant potential of photonic systems for the recovery of low-grade waste heat.

    View details for DOI 10.1021/acs.nanolett.8b02184

    View details for Web of Science ID 000441478300084

    View details for PubMedID 30016115

  • High-performance near-field thermophotovoltaics for waste heat recovery NANO ENERGY Zhao, B., Chen, K., Buddhiraju, S., Bhatt, G., Lipson, M., Fan, S. 2017; 41: 344–50
  • Resonance perfect absorption by exciting hyperbolic phonon polaritons in 1D hBN gratings OPTICS EXPRESS Zhao, B., Zhang, Z. M. 2017; 25 (7): 7791-7796


    Natural materials with hyperbolic responses can confine light with well-defined propagation directions inside the micro/nanostructure. Here we theoretically demonstrate that strong resonance absorption can be achieved in one-dimensional gratings made of hexagonal boron nitride (hBN) due to hyperbolic phonon polaritons. The radiative properties of both trapezoidal and square resonators are calculated using anisotropic rigorous coupled-wave analysis. The resonance wavelengths can be theoretically predicted and are shown to follow the anomalous or traditional scaling laws depending on the hyperbolicity. These findings may benefit the applications including photodetection, color filters, and optomechanics.

    View details for DOI 10.1364/OE.25.007791

    View details for Web of Science ID 000398536000057

    View details for PubMedID 28380897