Theoretical Research On Thermoelectric Properties Of Metal Organic Coordination Polymers(MOCPs): Computational Design And Predictions

There is an abundance of heat that is rejected to the surroundings because of performance limitations of current heat engines.Thermoelectric materials,comprising p-and n-type semiconductors,can recover the waste heat and convert into electricity.Given that over 60%of usable heat is at temperatures below 250°C,low cost and large scale thermoelectric devices are required to economically utilize the waste heat.In this regard,conducting polymers constitute a suitable class of materials for low cost thermal power generation as they can be synthesized from abundant elements and can be processed with solution by using economic fabrication techniques.Furthermore,their low thermal conductivity and flexible nature permit new device architectures and applications.Despite these advantages,polymer-based thermoelectric devices have not made an impact.This is largely attributed to two factors:(i)the lack of high performance n-type polymers(power factor>10μW/m-K~2),and(ii)low power outputs(n W-μW)owing to impractical device design.Recently,benefiting from the rapid development of organic electronics,the research of organic thermoelectric(OTE)materials is receiving particular interest.Cooperation and complementation between organic and inorganic thermoelectric materials could promote the broader application of thermoelectric effect.To realize high conversion efficiency of thermoelectric device,high-performance p-and n-type OTE materials are both necessary.However,the instability of most n-type organic materials in air impedes their application for high-performance thermoelectric conversion.Therefore,more efforts should be made to promote relevant research and applications.Motivated by the recent experiments,we actually have investigated metal organic coordination polymer(MOCPs),i.e.(poly-nickel-ethylenetetrathiolate)poly(Ni-ett)through first principles band structure calculations and Boltzmann transport theory,as an efficient class of n-type polymers which are electrically conducting and stable in air,reported in recent experiments.MOCPs provide an intriguing platform to design functional thermoelectric materials through modifying metal atoms,organic ligands etc.Based on density functional theory(DFT)coupled with Boltzmann Transport theory,the thermoelectric properties of several MOCPs,which is designed by intercalating organic linkers ranging from benzene to pentacene between two inorganic units,have been investigated.We found that the interplay of d orbital of Ni atom andπorbitals of the organic linkers play an important role in band engineering and then in thermoelectric efficiency enhancement.Combining the high conductivity forπorbitals of organic ligands and large Seebeck coefficient of the d orbital of Ni atom,we have achieved the largest n-type power factor for one dimensional MOCPs.By using such intercalated MOCPs we have designed and predicted several high performance MOCPs through first principles calculations.Our calculations propose that this one dimensional conducting TE materials class have a unique feature to owe high electrical conductivity and large Seebeck coefficient at the same,due to unique band structure,can be very promising for potential applications in optothermoelectric devices and thermoelectric cooling devices at low temperature range.