Power Factor of One Molecule Thick Films and Length Dependence

Abstract

There is a rapidly increasing interest in organic thin film thermoelectrics. However, the power factor of one molecule thick organic film, the self-assembled monolayer (SAM), has not yet been determined. This study describes the experimental determination of the power factor in SAMs and its length dependence at an atomic level. As a proof-of-concept, SAMs composed of n-alkanethiolates and oligophenylenethiolates of different lengths are focused. These SAMs were electrically and thermoelectrically characterized on an identical junction platform using a liquid metal top-electrode, allowing the straightforward estimation of the power factor of the monolayers. The results show that the power factor of the alkyl SAMs ranged from 2.0 × 10–8 to 8.0 × 10–12 μW m–1 K–2 and exhibited significant negative length dependence, whereas the conductivity and thermopower of the conjugated SAMs are the two opposing factors that balance the power factor upon an increase in molecular length, exhibiting a maximum power factor of 3.6 × 10–8 μW m–1 K–2. Once correction factors about the ratio of effective contact area to geometrical contact area are considered, the values of power factors can be increased by several orders of magnitude. With a newly derived parametric semiempirical model describing the length dependence of the power factor, it is investigated that one molecule thick films thinner than 10 nm composed of thiophene units can yield power factors rivaling those of famed organic thermoelectric materials based on poly(3,4-ethylenedioxythiophene)/polystyrenesulfonate (PEDOT/PSS) and polyaniline/graphene/double-walled carbon nanotube. Furthermore, how the transition of the transport regime from tunneling to hopping as molecules become long affects power factors is examined.

Enhanced Thermopower of Saturated Molecules by Noncovalent Anchor‐Induced Electron Doping of Single‐Layer Graphene Electrode

“…i) Unsaturated hydrocarbons yield higher S values than saturated ones in the backbone of molecules. [ 1,20,22 ] ii) The S value increases with increasing π‐conjugation length of the backbone. iii) The electronic structural tuning in aryl molecules via substitution affects S .…”

Thermal Transport in Graphene Oxide Films: Theoretical Analysis and Molecular Dynamics Simulation

“…Although the thermal conductivity of GO films is inferior to that of graphene films, due to the influence of functional groups [16], the GO films still attract significant attention mainly because of the due to the influence of functional groups [16], the GO films still attract significant attention mainly because of the facile fabrication and low-cost features, which easily obtained in experiments and practical application. The thermal conductivity of GO films is much higher than that of polymerbased composites [17,18], the current materials for dissipating heat in electronics [19][20][21][22], thermoelectric technology, and heat managements [23][24][25][26][27][28][29]. Therefore, it is necessary to study the thermal properties of GO films to create high-quality heat applications for micro-electronic devices.…”

Complete mapping of the thermoelectric properties of a single molecule

“…

Theoretical studies suggest that mastering the thermocurrent through single molecules can lead to thermoelectric energy harvesters with unprecedentedly high efficiencies. [1,2,3,4,5,6] This can be achieved by optimizing molecule length, [7] optimizing the tunnel coupling strength of molecules via chemical anchor groups [8] or by creating localized states in the backbone with resulting quantum interference features. [4] Empirical verification of these predictions, however, faces considerable experimental challenges and is still awaited.

…”

“…Due to these difficulties, previous schemes typically relied on sequential measurements of the conductance G and the Seebeck coefficient S (refs. [2,7,8,9,10]) which can cause large errors in evaluating the power factor S G, because of molecular reconfiguration and drift in the measurement electronics. [10,11] Methods that provide G and S simultaneously fundamentally prevent applying gate and bias voltages.…”