Thermodynamic Analysis And Optimization Of Photon Enhanced Thermionic Emission

Solar energy is considered an inexhaustible clean and renewable energy.Photovoltaic solar cell and solar thermal converters are currently the main solar energy utilization methods.Photon-enhanced thermionic emission(PETE)is a new concept of solar photoelectric conversion technology,which can effectively utilize the fullspectrum of solar energy and achieve higher energy conversion efficiency.The theoretical model and thermodynamic analysis for PETE energy conversion were completed.The design of a PETE performance test system and the experiments under different working conditions were carried out.The effects of space charge were optimized.The thermal-electronic-thermodynamic coupling model of the PETE conversion was established,and the energy flows and irreversible losses were evaluated.The exergy distributions under different output voltage,electron affinity,anode temperature and concentration ratio are analyzed.The surface affinity lower than 0.702 eV and the anode temperature of 645 K were the optimal parameters.By analyzing the performance of PETE devices,photovoltaic devices and thermionic devices under different working parameters,the role of photon-thermal synergistic enhancement effect in PETE energy conversion was verified.A vacuum PETE performance test system was designed.The amorphous silicon was used as the cathode and the I-V characteristic curves were obtained to analyze the performance of PETE system under different temperatures,luminous intensities,and spectrum.The effect of ion current on the output characteristic was considered.The ion current had a significant effect when the output voltage is larger than 1V or smaller than-1V.At 350℃,2.2W light increased the output power by 0.467μW,4 times that under no light condition.The cathode had different spectral response capabilities to different monochromatic light.The quantum efficiency cased by carrier excitation reached the highest at 300 nm,and the increase in temperature can improve the conversion efficiency of the cathode.The influence of different spacing and cesium vapor concentration on the space charge effect was studied experimentally.As the distance between the electrodes was shortened from 120μm to 30μm,the short-circuit current was increased from 0.76 mA to 5.67 mA,which is equivalent to a reduction of the space charge barrier by 0.1eV.In terms of output power,the maximum power was increased from 184μW to 907μW,and the corresponding output voltage was reduced from 0.5V to 0.35 V.As the temperature of cesium was increased from 200℃ to 350℃,the short-circuit current increased from9.76 mA to 23.3mA,and the maximum output power increased from 1.41 mW to 3.19 mW.