Experimental and theoretical study on hybrid thermionic-photovoltaic energy converters with graphene/semiconductor Schottky junction

Both thermionic and thermophotovoltaic solid-state energy converters are being actively explored due to high output potential. Recently, hybrid thermionic-photovoltaic (TIPV) approaches was proposed to utilize both electrons and photons emitted by a high temperature cathode, whereas conventional two-terminal configuration is constrained by current-match. In this work, we develop a four-terminal TIPV converter with a dispenser cathode, a transparent indium-tin-oxide anode and tandem graphene/GaAs Schottky junction photovoltaics. The TI and PV sub-devices can operate independently without meeting the current-match constraint. The TIPV prototype yields a power density of 962 W/m(2) at the cathode temperature of 1373 K. In addition, a threeterminal TIPV converter with Nano-scale electrode gap size is modelled with advantages of surface plasmon and evanescent wave tunnelling. Results demonstrate that Super-Planckian near-field enhancement guarantees a > 4 MW/m(2) output power density for the converter. We also discuss the effects of electrode gap size and the cathode temperature. This work validates the TIPV converters with graphene/semiconductor Schottky junction and also paves a way to promising developments for the Super-Planckian near-field configuration.