The impact of film deposition and annealing on the nanostructure and dielectric constant of organic semiconductor thin films.

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dc.contributor.authorPackman, L.
dc.contributor.authorMallo, N.
dc.contributor.authorRaynor, A.
dc.contributor.authorGao, M.
dc.contributor.authorBabazadeh, M.
dc.contributor.authorJin, H.
dc.contributor.authorHuang, D.M.
dc.contributor.authorBurn, P.L.
dc.contributor.authorGentle, I.R.
dc.contributor.authorShaw, P.E.
dc.date.issued2023
dc.description.abstractThe strategy of using a bulk-heterojunction light-absorbing layer has led to the most efficient organic solar cells. However, optimising the blend morphology to maximise light absorption, charge generation and extraction can be challenging. Homojunction devices containing a single component have the potential to overcome the challenges associated with bulk heterojunction films. A strategy towards this goal is to increase the dielectric constant of the organic semiconductor to ≈10, which in principle would lead to free charge carrier generation upon photoexcitation. However, the factors that affect the thin film dielectric constants are still not well understood. In this work we report an organic semiconductor material that can be solution processed or vacuum evaporated to form good quality thin films to explore the effect of chromophore structure and film morphology on the dielectric constant and other optoelectronic properties. 2,2'-[(4,4,4',4'-Tetrakis{2-[2-methoxyethoxy]ethyl}-4H,4'H-{2,2'-bi[cyclo-penta[2,1-b:3,4-b']dithiophene]}-6,6'-diyl)bis(methaneylylidene)]dimalononitrile [D(CPDT-DCV)] was designed to have high electron-affinity end groups and low ionisation-potential central moieties. It can be processed from solution or be thermally evaporated, with the film morphology changing from face-on to a herringbone arrangement upon solvent or thermal annealing. The glycol solubilising groups led to the static dielectric constant (taken from capacitance measurements) of the films to be between 6 and 7 (independent of processing conditions), while the optical frequency dielectric constant depended on the processing conditions. The less ordered solution processed film was found to have the lowest optical frequency dielectric constant of 3.6 at 2.0 × 10¹⁴ Hz, which did not change upon annealing. In contrast, the more ordered evaporated film had an optical frequency dielectric constant 20% higher at 4.2 and thermal annealing further increased it to 4.5, which is amongst the highest reported for an organic semiconductor at that frequency. Finally, the more ordered evaporated films had more balanced charge transport, which did not change upon annealing.
dc.description.statementofresponsibilityLachlan Packman, Neil Mallo, Aaron Raynor, Mile Gao, Mohammad Babazadeh, Hui Jin, David M. Huang, Paul L. Burn, Ian R. Gentle, and Paul E. Shaw
dc.identifier.citationPhysical Chemistry, Chemical Physics - PCCP, 2023; 25(35):23867-23878
dc.identifier.doi10.1039/d3cp03038e
dc.identifier.issn1463-9076
dc.identifier.issn1463-9084
dc.identifier.orcidHuang, D.M. [0000-0003-2048-4500]
dc.identifier.urihttps://hdl.handle.net/2440/139623
dc.language.isoen
dc.publisherRoyal Society of Chemistry
dc.relation.granthttp://purl.org/au-research/grants/arc/LE170100144
dc.rights© the Owner Societies 2023
dc.source.urihttps://doi.org/10.1039/d3cp03038e
dc.titleThe impact of film deposition and annealing on the nanostructure and dielectric constant of organic semiconductor thin films.
dc.typeJournal article
pubs.publication-statusPublished

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