Thermal resistances of thin films of small molecule organic semiconductors

Abstract

Abstract:We have measured the thermal resistances of thin films of the small molecule organic semiconductors bis(triisopropylsilylethynyl) pentacene (TIPS-pn), bis(triethylsilylethynyl) anthradithiophene (TES-ADT) and difluoro bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT). For each material, several films of different thicknesses have been measured to separate the effects of intrinsic thermal conductivity from interface thermal resistance. For sublimed films of TIPS-pn and diF-TES-ADT, with thicknesses ranging from < 100 nm to > 4 µm, the thermal conductivities are similar to that of polymers and over an order of magnitude smaller than that of single crystals, presumably reflecting the large reduction in phonon mean-free path in the films. For thin (≤ 205 nm) crystalline films of TES-ADT, prepared by vapor-annealing spin-cast films, the thermal resistances are dominated by interface scattering.

Frequency-dependent photothermal measurement of thermal diffusivity for opaque and non-opaque materials: Application to crystals of TIPS-pentacene

“…This assumption led us to a very large value of the interlayer diffusivity and thermal conductivity, values an order of magnitude larger than generally found in organic materials, which we tentatively associated with interactions between rotations of the TIPS sidegroups which extend between the layers of the crystal. However, subsequent measurements on sublimed thin films of TIPS-pentacene deposited on substrates 14 gave a value for the interlayer thermal conductivity two orders of magnitude smaller than the value we calculated for crystals in Ref. [6].…”

“…measurements 14 and values expected for a layered organic crystal; for example, this value is much smaller than the needle-axis diffusivity, 5 as expected.…”

“…5 This value of κ c is 65% larger than the value found for sublimed films, 14 and the difference can be readily associated with disorder in the films: from the analysis of Ref. [14], if one assumes that the heat is carried by acoustic phonons only, the value of κ c implies a phonon mean-free path of 3-4 c (the interlayer spacing) in the crystal and ~ 2c in the film. The value of κ c in the crystal is also about twice that found for crystals of rubrene, 9 another layered small molecule organic semiconductor.…”

Thermal conductivity of benzothieno-benzothiophene derivatives at the nanoscale

“…The in-plane κ of various molecular thin films ( pentacene, TPD, Alq3, C 60 , PCBM, rubrene, DNTT, ….) 4, [18][19][20][21][22][23][24][25][26] has been measured in the range 0.1-0.8 W m −1 K −1 at the macroscale (ac-calorimetry, 3ω Joule heating, time domain thermo-reflec-tance….). Only a very few reports have been published on the out-of-plane κ of these organic materials at the nanoscale, e.g.…”

Strong Suppression of Thermal Conductivity in the Presence of Long Terminal Alkyl Chains in Low‐Disorder Molecular Semiconductors

“…[ 27 ] More recently, very low values of thermal conductivity were also found in layered WSe 2 crystals – which was speculated to be caused by phonon localization induced by random stacking of 2D crystalline thin sheets [ 28 ] —and in the fullerene derivatives PCBM and PCBNB [ 29,30 ] —which was explained, similarly to C 60 /C 70 , by localization of vibrational modes of the rigid buckyball molecules. The in‐plane and out‐of‐plane thermal conductivities of various systems (pentacene, Alq 3 , C 60 , rubrene, TIPS‐pentacene, CuPc) [ 31–36 ] with sample ranging from polycrystals to single crystals, have been measured macroscopically using techniques such as ac‐calorimetry, the 3ω method or time domain thermoreflectance measurements and have been found to be in the range 0.1–0.8 W m –1 K –1 . However, a detailed understanding of structure–property relationships remains elusive.…”