Tianjun Liao

Effects of nanoscale vacuum gap on photon-enhanced thermionic emission devices

A new model of the photon-enhanced thermionic emission (PETE) device with a nanoscale vacuum gap is established by introducing the quantum tunneling effect and the image force correction. Analytic expressions for both the thermionic emission and tunneling currents are derived. The electron concentration and the temperature of the cathode are determined by the particle conservation and energy balance equations. The effects of the operating voltage on the maximum potential barrier, cathode temperature, electron concentration and equilibrium electron concentration of the conduction band, and efficiency of the PETE device are discussed in detail for different given values of the vacuum gap length. The influence of the band gap of the cathode and flux concentration on the efficiency is further analyzed. The maximum efficiency of the PETE and the corresponding optimum values of the band gap and the operating voltage are determined. The results obtained here show that the efficiency of the PETE device can be sig...

Negative illumination thermoradiative solar cell

The negative illumination thermoradiative solar cell (NITSC) consisting of a concentrator, an absorber, and a thermoradiative cell (TRC) is established, where the radiation and reflection losses from the absorber to the environment and the radiation loss from the TRC to the environment are taken into consideration. The power output and overall efficiency of the NITSC are analytically derived. The operating temperature of the TRC is determined through the thermal equilibrium equations, and the efficiency of the NITSC is calculated through the optimization of the output voltage of the TRC and the concentrating factor for a given value of the bandgap. Moreover, the maximum efficiencies of the NITSC at different conditions and the optimal values of the bandgap are determined, and consequently, the corresponding optimum operating conditions are obtained. The results obtained here will be helpful for the optimum design and operation of TRCs.

Graphene-Based Thermionic Solar Cells

A model of the graphene-based thermionic solar cell (TSC) consisting of a concentrator, an absorber, and a thermionic emission device configured with graphene-based cathode is proposed, where the radiation and reflection losses from the absorber to the environment, the thermal radiation between the cathode and the anode electrodes, and the heat losses from the anode to the environment are considered. The performance characteristics of the TSC are analyzed by numerical calculations. It is found that the maximum efficiency can reach 21% when the area ratio is 0.24 and the voltage output is 2.01 V. In addition, the maximum efficiencies of the TSC under different concentrations and the optimal values of some key parameters are determined, and consequently, the corresponding optimally operating conditions are obtained. The results obtained here may provide guidance for the appropriate selection of electrode materials and the optimum design of practical TSC devices.

Spin-Seebeck Temperature Sensors

The conceptual designs of two nanoscale spin-Seebeck temperature sensors are proposed based on the longitudinal spin-Seebeck effect (LSSE) in bilayers made of a ferromagnetic insulator Y3Fe5O12 and a Pt, and the transverse spin-Seebeck effect) in Ni81Fe19/Pt structure. The working principles of two sensors are presented. The direct conversion of the temperature information into the electric voltage is described in detail. Moreover, the effect of the spin Hall angle on the performance of sensors is discussed. The results obtained here reveal that the LSSE and TSSE have the potential to realize practical temperature sensors.

Performance Evaluation and Parametric Optimum Choice Criteria of a Near-Field Thermophotovoltaic Cell

Based on the near-field (NF) model of a thermophotovoltaic cell (TPVC) consisting of an emitter and a photovoltaic (PV) cell separated by a vacuum gap, two important formulas for the power output and efficiency are analytically derived by using fluctuation electrodynamics theory. The general performance characteristics of the NF-TPVC are evaluated. The optimum choice criteria of several key parameters, such as the power output density, efficiency, and distance of the vacuum gap of the TPVC, the current density and voltage output of the PV cell, and the band-gap of semiconductor materials in the PV cell, are supplied. Moreover, the maximum power output densities and efficiencies of three NF-TPVCs made of InSb, InAs, and InGaAsSb are calculated and the corresponding optimum values of other parameters are determined. The results obtained may provide some theoretical guidance for engineers to optimally design NF-TPVCs.