Based On The Mechanism Of Photon-enhanced Electron Emission For Solar Energy Converters

A novel concept for solar electricity generation, Photon Enhanced ThermionicEmission (PETE), was recently proposed for harvesting solar photonic andthermionic energy simultaneously. The relative investigations show that theconversion efficiency of PETE can exceed40%theoretically. Currently, research onPETE solar devices is not thorough, previous PETE studies on the use of solarenergy are stuck in theoretical research. Report for PETE device design andpreparation are yet seen. In this paper, based on the establishment of an improvedPETE theoretical model, optimization parameters of PETE device and an efficientintegration of PETE hybrid system are obtain. A PETE device based ontransmission-type GaAs cathode is prepared. It is demonstrated that PETE integratedsystem synthesize solar photovoltaic/solar thermal effect, which is instructive for thedepth research on PETE solar utilization. The specific contents are as following:Firstly, based on the establishment of theoretical model for PETE device, theeffect of PETE device anode and cathode material on conversion efficiency isinvestigate and the key parameters of PETE convertor are optimized. Comparing avariety of high-temperature photoemission material, The GaAs material is select asthe efficient PETE cathode. It is propose that a gradient doped structure can improveelectron transport in PETE cathode and emission efficiency. Based on the analysis ofPETE hybrid system energy transfer, at200sun concentration and cathodetemperature with1000K, the overall system efficiency can reach25%, where theefficiency PETE convertor is20%.Secondly, a PETE convertor is developed based on the design of structure andthe production process of transmission PETE device. High quality GaAs PETEcathode with exponential doping structure is prepared by MOCVD technology. It isdemonstrated the epitaxial GaAs material has a good PETE characteristics by theexperiment of electric field induced GaAs PETE. A diamond thin film material withwork function of1.1eV is achieved by hot filament CVD method, which can play therole of anode for the PETE convertor. Through ohmic contact processing andvacuum packaging technology, the vacuum of the PETE device is obtained. Csactivation treatment is carried out in high vacuum, and sensitivity of200mA/W ismeasured at temperature of400for the visible light, which conversion efficiencyis about10%.Thirdly, integration of PETE hybrid system is designed for PETE solarphotovoltaic/solar thermal combined experimental. The results show that the PETE device cathode temperature is600K and PETE device system conversion efficiencyis1.5%at64times sunlight concentrating. Through heat insulation treatment for thedevice surface, the experimental results can be significantly improved. It is inferredfrom the experimental results that if the combined system under standard daylightconditions, namely with200suns concentrating, the PETE cathode operatingtemperature will be close to1000K and the device conversion efficiency can reach15%.Lastly, the feasibility of a reflective PETE device is analysis, and usingfemtosecond laser processing of solar cell materials technology,“light trapping”microstructure is prepared on the surface of reflective GaAs cathode with purpose ofreinforcement sunlight absorption. Comparative study abroad PETE studies,innovations of this thesis are as follows:The PETE electron diffusion-emission model is established and the gradientdoped structure proposed to improve the PETE conversion efficiency.A transmission PETE device is achieved using vacuum packaging technology,which effectively overcome the pn junction failure of PV with the increase ofoperating temperature.A combination of concentrator technology, the principle of photon enhancedthermionic emission (PETE) and based on the Seebeck effect thermoelectric powergeneration technology is carried out.