Thermophotovoltaic Energy Conversion With Ga_xIn_1-xAs_ySb_1-y/InAs_0.91Sb_0.09 Dual-junction Cell

Thermophotovoltaic cell is the key component of thermophotovoltaic system to convert thermal radiation energy into electric energy,limiting the final power output and energy conversion efficiency of the whole thermophotovoltaic system.Given that the large mismatch between the spectral response of traditional single-junction thermophotovoltaic cells and the broad thermal radiation of generally economical radiators,in this thesis,taking experimentally-accessible yet Ga Sb lattice-matched Ga_xIn_1-xAs_ySb_1-y and InAs_0.91Sb_0.09 alloys,a new type of Ga_xIn_1-xAs_ySb_1-y/InAs_0.91-Sb_0.09 dual-junction thermophotovoltaic cell are theoretically proposed and systematically investigated to achieve better thermophotovoltaic energy conversion.By applying classical drift-diffusion theory,the influence of the thermal spectrum of radiator,the bandgap of top subcell,and cell temperature on thermophotovoltaic energy conversion of dual-junction cell are detailedly examined,obtaining some meaningful results to guide the experiments,which are briefly summarized as follows:1 Ga_0.84In_0.16As_0.14Sb_0.86/InAs_0.91Sb_0.09 dual-junction cell.With Ga Sb lattice-matched Ga_0.84In_0.16As_0.14Sb_0.86 and InAs_0.91Sb_0.09alloys,a new Ga_0.84In_0.16As_0.14-Sb_0.86/InAs_0.91Sb_0.09 dual-junction cell is theoretically studied to uncover the fundamental role of dual-junction cell in boosting the thermophotovotlaic energy conversion.It is shown that the optimal doping profile of top subcell as N_d,t=12×10¹⁷cm³ and N_a,t=6×10¹⁷cm³,while the optimal doping profile of bottom subcell as N_d,b=10×10¹⁷cm³ and N_a,b=1×10¹⁷cm³.Without any spectral management,efficiency beyond 13%for blackbody radiator operating at the temperature ranging from 1700to 2000 K.Comparing to that for Ga_0.84In_0.16As_0.14Sb_0.86 single-junction cell,the net improvement in efficiency can be larger than 3%,fully demonstrating the important role of dual-junction cell in enhancing thermophotovoltaic energy conversion.2 The influence of top subcell bandgap(E_g,t)on thermophotovoltaic energy conversion of Ga_xIn_1-xAs_ySb_1-y/InAs_0.91Sb_0.09 dual-junction cell.Based on the experimentally-available yet Ga Sb lattice-matched Ga_xIn_1-xAs_ySb_1-y alloy,the effect of top subcell bandgap on thermophotovoltaic energy conversion achieved by Ga_xIn_1-xAs_ySb_1-y/InAs_0.91Sb_0.09 dual-junction cell is systematically investigated with a two-step method.It is demonstrated that the effect of radiator temperature and top subcell bandgap on the optimum structure of dual-junction cell as well as its performance outputs can be quantitatively described by a pair of phenomenological equations,which provides some useful theoretical guidelines to design and fabricate proper dual-junction cell for the specific environment.Secondly,free of any spectral management,with the increase of the top subcell bandgap,the maximum conversion efficiency of the dual-junction cell increases from 12.928%at E_g,t=0.50 e V to13.924%at E_g,t=0.60 e V,showing a net efficiency increase of about 1%.3 The effect of cell temperature（T_C）on thermophotovoltaic energy conversion of Ga_xIn_1-xAs_ySb_1-y/InAs_0.91Sb_0.09 dual-junction cell.To examine the effect of high density thermal shock on the structure and performance of dual-junction thermo-photovoltaic cell,the influence of cell temperature on the structure and performance of Ga_xIn_1-xAs_ySb_1-y/InAs_0.91Sb_0.09 dual-junction cell is further investigated.It is shown that with the increase of cell temperature,the structure and performance of the dual-junction cell show significant nonlinear evolution behavior,and the conventional temperature coefficients are valid only at near room temperature.Secondly,based on the calculated data,a phenomenological method to describe the evolution of temperature-dependent properties in a broader temperature range is formulated by fitting the received bandgap and spectrum-dependent evolutions.