| The radioisotope thermophotovoltaic（RTPV）system is a system that converts the thermal energy generated by the decay of the isotope heat source into the electrical energy of the photovoltaic cell through the photovoltaic effect.Compared with other static isotope batteries,they have higher mass specific power and energy conversion efficiency,and have great potential for application.The RTPV system consists of components such as isotope heat sources,emitters,filters,anti reflection films,photovoltaic cells,and heat dissipation devices.The emitter can convert heat from a heat source into radiant energy,and its radiation spectrum directly affects system performance.By designing the microstructure of a selective emitter,its radiation spectrum can be regulated,effectively improving emission characteristics,reducing battery parasitic heat,optimizing energy flow,and improving system performance.In this paper,selective emitters matching the band gap of InGaAsSb cell are designed.The influence of different structural parameters on emissivity is studied by using the Finite Difference Time Domain（FDTD）method,and the radiation enhancement mechanism is discussed.The reliability of simulation results is verified by using LC equivalent circuit model.The particle swarm optimization（PSO）algorithm is used to optimize the 2D single size,multi size and 3D emitters,and the optimization schemes of the two dimensions are proposed.The results indicate that,based on existing system theoretical efficiency calculation models,the designed emitters can effectively improve spectral performance and system performance compared to flat emitters under specific conditions.In terms of two-dimensional micro structure emitter,for W-Al2O3-W wavelength selective emitter,the influence of structural parameters such as micro structure period a,surface unit width w,surface unit height h and dielectric layer thickness d on emissivity is studied,and the optimization design is carried out,and a preliminary optimization scheme of single size emitter is proposed.For the existing equivalent LC circuit model theory,the influence of equivalent components on the prediction results is analyzed,and the simulation results of the single size emitter scheme are verified using this theory.Based on the single size emitter scheme and the analysis of radiation enhancement mechanism,the possibility and limitation of the multi size emitter scheme to further improve the system performance are discussed.Further more,the optimization design of the multi size emitter was carried out,and the structural parameters of the four size emitter matching the best scheme of the battery band gap width were determined,specifically,h=d=80nm;a=515nm;w1=354nm;w2=281nm;w3=242nm;w4=220nm.The radiation characteristics of the scheme are analyzed,including polarization and polarity insensitivity.When the emitter is substituted into a specific system with a emitter temperature of 1300K and a battery temperature of 300K,the electrical output power density of the system can reach 1.4313W/cm2,which is23.38%higher than that of the single size emitter scheme;The system efficiency can reach 25.13%,39.61%higher than that of the plane emitter and 135.96%higher than that of the Si C emitter.Similarly,in terms of three-dimensional core-shell micro structure emitter,the influence of structural parameters such as core radius r and shell thickness h of W-Al2O3-W wavelength selective emitter on emissivity was studied,and the scheme was optimized.Explored the similarities and differences in the radiation enhancement mechanism of three-dimensional emitter structures compared to two-dimensional emitters.Preliminary optimization schemes were proposed for both single-layer and multi-layer situations,and the optimal two-layer scheme was determined through comparison,its structural parameters are:h=150nm;r=451nm.By substituting it into a specific system with a emitter temperature of 1300K and a cell temperature of 300K,the electrical output power density reaches 1.2043W/cm2,which is 7.27%higher than that of a single layer;The system efficiency reaches 24.23%,which is 34.61%higher than the flat emitter and 127.51%higher than the Si C emitter.The radiation characteristics of the scheme are analyzed,including polarization and polarity insensitivity.And it was compared with the two-dimensional multi-size emitter scheme.Both have their own characteristics from different angles,but both have good spectral selectivity,which can significantly improve spectral efficiency and cell efficiency compared to non-selective emitters.From the perspective of electrical output power density,the two-dimensional four size emitter is determined as the final solution.Compared to the flat structure emitter,it has an increase in electrical power density of611.38%and a cell efficiency improvement of 39.61%.Compared to the non-selective Si C emitter,it has an increase in electrical power density of 11.59%and cell efficiency of 135.96%. |
