TY - JOUR

T1 - Thermoelectric properties of organic thin films enhanced by π-π stacking

AU - Wang, Xintai

AU - Sangtarash, Sara

AU - Lamantia, Angelo

AU - Dekkiche, Hervé

AU - Forcieri, Leonardo

AU - Kolosov, Oleg

AU - Jarvis, Samuel

AU - Bryce, Martin R.

AU - Lambert, Colin

AU - Sadeghi, Hatef

AU - Robinson, Benjamin

PY - 2022/4/30

Y1 - 2022/4/30

N2 - Thin films comprising synthetically robust, scalable molecules have been shown to have major potential for thermoelectric en-ergy harvesting. Previous studies of molecular thin-films have tended to focus on massively parallel arrays of discrete but iden-tical conjugated molecular wires assembled as a monolayer perpendicular to the electrode surface and anchored via a covalent bond, know as self-assembled monolayers. In these studies, to optimise the thermoelectric properties of the thin-film there has been a trade-off between synthetic complexity of the molecular components and the film performance, limiting the opportuni-ties for materials integration into practical thermoelectric devices. In this work, we demonstrate an alternative strategy for en-hancing the thermoelectric performance of molecular thin-films. We have built up a series of films, of controlled thickness, where the basic units – here zinc tetraphenylporphyrin – lie parallel to the electrodes and are linked via π-π stacking. We have compared three commonly used fabrications routes and characterised the resulting films with scanning probe and computation-al techniques. Using a Langmuir-Blodgett fabrication technique, we successfully enhanced the thermopower perpendicular to the plane of the ZnTPP multilayer film by a factor of 10, relative to the monolayer, achieving a Seebeck coefficient of -65 μV/K. Furthermore, the electronic transport of the system, perpendicular to the plane of the films, was observed to follow the tunnel-ling regime for multi-layered films, and the transport efficiency was comparable with most conjugated systems. Furthermore, scanning thermal microscopy characterisation shows a factor of 7 decrease in thermal conductance with increasing film thick-ness from monolayer to multilayer, indicating enhanced thermoelectric performance in a π-π stacked junction.

AB - Thin films comprising synthetically robust, scalable molecules have been shown to have major potential for thermoelectric en-ergy harvesting. Previous studies of molecular thin-films have tended to focus on massively parallel arrays of discrete but iden-tical conjugated molecular wires assembled as a monolayer perpendicular to the electrode surface and anchored via a covalent bond, know as self-assembled monolayers. In these studies, to optimise the thermoelectric properties of the thin-film there has been a trade-off between synthetic complexity of the molecular components and the film performance, limiting the opportuni-ties for materials integration into practical thermoelectric devices. In this work, we demonstrate an alternative strategy for en-hancing the thermoelectric performance of molecular thin-films. We have built up a series of films, of controlled thickness, where the basic units – here zinc tetraphenylporphyrin – lie parallel to the electrodes and are linked via π-π stacking. We have compared three commonly used fabrications routes and characterised the resulting films with scanning probe and computation-al techniques. Using a Langmuir-Blodgett fabrication technique, we successfully enhanced the thermopower perpendicular to the plane of the ZnTPP multilayer film by a factor of 10, relative to the monolayer, achieving a Seebeck coefficient of -65 μV/K. Furthermore, the electronic transport of the system, perpendicular to the plane of the films, was observed to follow the tunnel-ling regime for multi-layered films, and the transport efficiency was comparable with most conjugated systems. Furthermore, scanning thermal microscopy characterisation shows a factor of 7 decrease in thermal conductance with increasing film thick-ness from monolayer to multilayer, indicating enhanced thermoelectric performance in a π-π stacked junction.

U2 - 10.1088/2515-7655/ac55a3

DO - 10.1088/2515-7655/ac55a3

M3 - Journal article

VL - 4

JO - J. Phy. Energy

JF - J. Phy. Energy

SN - 2515-7655

IS - 2

M1 - 024002

ER -