Abstract
It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. We here isolate the intrinsic factors affecting either electron or hole transport within the same film microstructure of a model copolymer semiconductor. Relatively, holes predominantly bleach inter-chain interactions with H-type electronic coupling character, while electrons’ relaxation more strongly involves intra-chain interactions with J-type character. Holes and electrons mobility correlates with the presence of a charge transfer state, while their ratio is a function of the relative content of intra- and inter-molecular interactions. Such fundamental observation, revealing the specific role of the ground-state intra- and inter-molecular coupling in selectively assisting charge transport, allows predicting a more favorable hole or electron transport already from screening the polymer film ground state optical properties.
Highlights
It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture
Though interfacial phenomena can play a major role in unbalancing the charge transport of the two carriers, the tickling question regards the influence of polymer chain chemical composition and solid-state microstructure on a preferential hole or electron transport
While no absolute mobility values can be extracted from absorption spectra due to the lack of a universal quantitative model, we show that the spectral variations observed on different polymer films, including the ones reported here and in the previous literature, contain the necessary information for predicting the expected mobility trend in the investigated polymer films
Summary
It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. Bredas et al investigated, from a theoretical point of view, the role played by parameters such as chemical composition, backbone planarity, and extension of intramolecular and intermolecular π–π conjugation, in selectively affecting hole and electron-hopping transport[25] They gathered attention on the strong impact played by the relative distance and orientation of neighboring chromophores, and on the superposition of their outer molecular orbitals. Of the order of a fraction of an angstrom, can determine a wide variation in the chromophores’ electronic coupling, having an impact on holes and/or electrons charge transfer (CT) probability Such information is clearly embedded in the semiconductor ground-state spectra at the solid state, but until now, no keys have been provided to obtain hole and/or electron mobility insights from such spectra, a clear limitation to their predictive power. Such predictability would be fundamental for identifying those design principles that can boost further the desired unipolar or ambipolar transport properties of new polymers
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