Molecular Packing of High-Mobility Diketo Pyrrolo-Pyrrole Polymer Semiconductors with Branched Alkyl Side Chains

Abstract

We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm(2) V(-1) s(-1), with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases. Thermal annealing generally reduces both the face-on population and the misoriented edge-on domains. The highest hole mobilities of this series were obtained from edge-on molecular packing and in-plane liquid-crystalline texture, but films with a bimodal orientation distribution and no discernible in-plane texture exhibited surprisingly comparable mobilities. The high hole mobility may therefore arise from the molecular packing feature common to the entire polymer series: backbones that are strictly oriented parallel to the substrate plane and coplanar with other backbones in the same layer.

Structure and Morphology Control in Thin Films of Conjugated Polymers for an Improved Charge Transport

“…All these improvements could be reflected by the red-shifted absorption spectra and/or the increased value of A 0-0 /A 0-1 . Fortunately, the J-aggregation has been found in poly(3-hexylthiophene) (P3HT) [36] and many donor-acceptor copolymers with extended intra-chain conjugation and a good planarity in their backbones [37][38][39]. By strategies such as choosing processing solvent with a high boiling point [31], dispersing the nanofibrils [40] and thermal annealing [38,39], etc., the more ordered aggregation in films is strengthened corresponding to the red-shifted absorption, enhanced A 0-0 /A 0-1 value, more ordered fibrillar morphology and improved mobility.…”

“…Meanwhile, slow evaporation of solution in CS 2 [60], CS 2 vapor annealing [61], vapor-assisted imprinting [57] and thermal nano-imprinting [62] have been employed to acquire flat-on molecular orientations in P3AT films. For FETs, although some donor-acceptor copolymers such as poly(diketo pyrrolo-pyrrole-co-thiophene) (PDPP-T) and poly{[N,N9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)} [P(NDI2OD-T2)] display high mobility in spite of a mainly face-on orientation [37,63], the edge-on molecular orientation of chains respect to substrates is favored for most conjugated polymers because of the in-plane π-π pathways wanted by device architecture. The devices with edge-on orientations have a better mobility than those with face-on orientations in examples like P3HT and pBTTT et al [59,64,65].…”

“…Firstly, extending the conjugation system and strengthening intra-chain and inter-chain interaction is a direct way to improve electronic properties. Based on the classic conjugated polymers such as P3ATs (P1), a straight strategy is inserting more conjugated moieties [3,82] such as carbon double bond (-HC=CH-, P2) [83][84][85], unsubstituted multiple or fused aromatic rings (i.e., thiophenes and thieno[3,2-b]thiophene, etc., P3-P7) [13,14,16,37,82,[86][87][88][89][90][91], other heterocyclic rings containing nitrogen(and sulfur) (P8 and P9) or selenium atoms (P10) [13,15,81,[92][93][94][95][96][97] and their combination (P11) [98]. Thus, the intra-chain conjugation is extended and strengthened by coupling with the more conjugated moieties, and the conjugation length is elongated due to the improved planarity.…”

“…Many high-mobility copolymers based on dithienyl-DPPs have been synthesized through coupling with intensely conjugated p-type moieties such as thieno [3,2-b]thiophene, unsubstituted dithiophene, diselenophene, benzothiadiazole, etc. (P12-P16) [11,37,[104][105][106]. The conjugated polymer with extremely high carrier mobilities so far has been synthesized by combining dithienyl-DPP and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene moieties (P15b) [106] and [1,2-bis(5-(thiophen-2-yl)selenophen-2-yl]ethene (P16) [17], which are intense conjugated n-type [11] and p-type moieties [83,94], respectively.…”

Modified structure of two-dimensional polythiophene derivatives by incorporating electron-deficient units into terthiophene-vinylene conjugated side chains and the polymer backbone: synthesis, optoelectronic and self-assembly properties, and photovoltaic application

“…3, P1 thin lm possesses a visible (100) diffraction peak at 2q ¼ 3.01 (corresponding to an interlayer d-spacing of 2.54 nm with an average crystallite size of 16.5 nm), indicating lamellar packing parallel to the surface normal with an edge-on (100) orientation of the conjugated plane. 40 As two hydrogen atoms were replaced by two heptanoyl substituents at 5 and 5 00 positions of the terthiophene side chain of P1, polymer P2 thinlm displayed amorphous nature that indicating the more bulky side groups in P2 hinder the molecular stacking. Therefore, although the additional two heptanoyl groups in TTV side chains could enhance the solubility and red-shi absorption in UV-vis region, it is destructive for polymer self-assembly and backbone coplanarity by larger side chains.…”