The Defect Regulation Of FASnI₃ Perovskite Films And The Research On Their Thermoelectric Properties

Realizing direct conversion from thermal energy to electrical energy,thermoelectric materials have been widely used in the fields of aerospace and portable electronic equipment with the advantages of noiselessness and no serious pollution.Organic-inorganic hybrid perovskites（OHPs）have been considered as potential high-quality thermoelectric materials with high mobility and low thermal conductivity,originating from the alternating arrangement structure of the organic and inorganic skeleton,which is beneficial to carrier transport and phonon scattering.As a lead-free environment-friendly material,tin-based perovskite with oxidation self-doping of tin（II）can greatly improve the concentration of carriers and conductivity to increase the thermoelectric conversion efficiency.Meanwhile,the defects resulting from the oxidation of tin（II）and the rapid crystallization rate of tin-based perovskite have been an enormous challenge for further improving thermoelectric properties.Further promoting the enhancement of thermoelectric properties for tin-based perovskite,the crystallization growth process and defect density of tin-based perovskite could be well regulated by doping with external metal ions and simple component engineering,thus realizing the simultaneous improvement of thermoelectric properties and stability.The specific work is as follows:Firstly,in the FASnI₃ tin-based perovskite,the Bi³⁺doping is used to regulate the chemical structure,lattice formation,and defect density,beneficial to improving the film morphology,which could reduce the ion migration at the grain boundary,and modifying the carrier transport,eventually improving thermoelectric properties.The different proportions of Bi I₃（0 mol%,1 mol%,3 mol%,5 mol%）were doped in FASnI₃ thin films,then optical and physical properties were characterized.It shows that Bi³⁺doping can effectively improve the crystallization process of perovskite,optimize the morphology of the thin films,reduce the defect density,and delay the oxidation of the thin films.The thermoelectric test shows that the conductivity,Seebeck coefficient,and power factor of FASnI₃ thin films are improved in different proportions.With 3 mol%Bi I₃ doping,the FASnI₃ perovskite achieved the highest electrical conductivity(18.3 S·cm^-1)and the best power factor(41.2μW·m^-1·K^-2)with about 20 times power factor higher than that of the undoped initial one.This work shows that doping of Bi I₃ can reduce the defects of tin-based perovskite and improve its.However,such a Bi³⁺doping strategy could limitedly improve the thermoelectric performance,which shows a significant gap with the current high-performance thermoelectric materials.Secondly,the tin-rich strategy is applied to reduce the tin vacancy defects and improve the carrier transport performance and stability in tin-based perovskite.We studied the effect of simple component adjustment engineering on the thermoelectric properties of tin-based perovskite for the first time.By directly amplifying the proportion of SnI₂,with excess SnI₂ of 0 mol%,10 mol%,20 mol%,and 30 mol%,various FASnI₃ films were prepared,and their related properties were investigated.It has been found that different from conventional Sn F₂ to provide a tin-rich environment,and this simple strategy can effectively reduce the density of defective states in thin films and improve mobility while maintaining high carrier concentration to improve conductivity.The thermoelectric performance test results show that this strategy can greatly improve the conductivity and power factor.Finally,under 20 mol%-SnI₂,the optimal power factor of 124μW·m^-1·K^-2 and the conductivity of 52.4 S·cm^-1 are obtained,which is the highest level of organic-inorganic hybrid perovskite thermoelectric materials at present.Meanwhile,the excess SnI₂ deposited on the surface of the film greatly improves the stability of the film.After 90 minutes of oxidation in the air,the thermoelectric property remains at 5%for the 20 mol%-SnI₂-based FASnI₃ film,while the pure FASnI₃ film degrades after half an hour.These results indicate that it is an efficient strategy to improve the thermoelectric properties and stability of tin-based perovskite films by modestly increasing the proportion of tin components through simple component engineering.