Preparation And Thermoelectric Properties Of Perovskite Cs₃Bi₂I₉ Single Crystal

Thermoelectric materials can realize the conversion of thermal energy to electrical energy,and have huge application prospects in the energy industry.Perovskite Cs₃Bi₂I₉ has a large atomic number,which can cause vibrational anharmonicity;it has a low thermal conductivity,and the layered structure is beneficial to reduce heat conduction;at the same time as a semiconductor material,it can adjust electrical properties and theoretically have a certain thermoelectricity performance.In this paper,Cs₃Bi₂I₉ crystal was grown by electric control gradient solidification method and reverse temperature evaporation crystallization method,and the thermoelectric properties of Cs₃Bi₂I₉ crystal were studied.Firstly,the solid-phase grinding method is used to prepare the Cs₃Bi₂I₉ raw material polycrystalline powder,and the crystal is prepared by an improved dual-temperature zone electronically controlled gradient solidification method.The effect of convection temperature,growth rate,and cooling rate on the quality of Cs₃Bi₂I₉ crystals was systematically studied,and it was found that the upper temperature zone of convection temperature was 628?,the lower temperature zone was 682?,the growth rate was 0.5mm/h,and the cooling rate was 6?/h.The surface of the obtained crystal is smooth and flat.The XRD test shows that the crystal can grow along the(l00)and(00l)directions,which proves the layered structure of the material;the EDS test shows that the atomic ratio of each element in the crystal growth process is Cs:Bi:I=2.76:2:8.22,there is in the absence of I element;rough calculation by the Tauc curve of Cs3Bi₂I₉ perovskite single crystal,the forbidden band width of the crystal is about 1.98 e V.The I-V curve test calculates that the resistivity of the crystal is on the order of 10¹⁰?·cm.Through the test,it is found that the Seebeck coefficients are all negative values.The Cs₃Bi₂I₉ crystal is an n-type semiconductor material,and the maximum Seebeck coefficient is about-310.12?V/K.Secondly,the Cs₃Bi₂I₉ crystal was prepared by the reverse temperature-evaporative crystallization method.The effect of the crystal growth temperature,the number of openings,and the presence or absence of seeds on the quality of the crystal was systematically studied.It was found that the growth temperature was 80?94?,the number of openings was 1,and the bottom of the container was put into 2 seed crystals in a short time.For large-size crystals,Cs₃Bi₂I₉ wafers can be cleaned more cleanly with DMF solution at 60?.The XRD test proves that the crystal can grow along the(l00)and(00l)directions with a hexagonal structure(spatial structure P6₃/mmc);The EDS test shows that the atomic ratio of each element in the crystal growth process is close to Cs:Bi:I=3.11:2:9.35;It is roughly calculated that the band gap of Cs₃Bi₂I₉ crystal is about 1.97 e V.Through the I-V curve test,it is calculated that the resistivity of the crystal is?=1.49×10¹⁰?·cm,and the Seebeck coefficient is negative.The Cs₃Bi₂I₉ crystal is an n-type semiconductor material,and the maximum Seebeck coefficient is about-698.46?V/K.