Further Examination of Interconnection in Conjugated Polymers for Organic Field‐Effect Transistors

Abstract

the source-drain electrodes. [4] Since the in-plane π-stacking is in line with the source and drain electrodes, likely further boosting the intermolecular charge transport along the two electrodes, the design principles toward conjugated polymers targeting at high OFET mobilities are thus directed to the establishment of extensive edge-on π-order. [5] Nevertheless, the longstanding principles have been challenged by several studies, in which decent hole or electron mobilities were achieved in the absence of the requirements. [6] Another emerging design principles are thus developed, stating that efficient charge transport in the polymer semiconducting layer can be accomplished through the interconnected short-range-order crystallites. [7] Conjugated polymers normally contain conjugated and aliphatic functionalities. [8] The aliphatic functionality is considered to be non-conductive. [9] It is envisioned that the interconnection among polymer crystallites encouraging the charge transport should primarily derive from the conjugated functionality. Herein it is coined as π-interconnection. In our interpretation, π-order and π-interconnection both stem from π-stacking. The crucial distinction lies in the degree of orderliness. In comparison with the π-order, the π-stacking in the π-interconnection is sporadic rather than periodic. On the other hand, our previous theoretical investigation sheds light on the stacking principles for π-stacking in organic semiconductors, suggesting that the resemblance in the molecular shape is responsible for the establishment of π-stacking. [10] It can thus be envisaged that for a given conjugated polymer with long aliphatic side chains, the fractional substitution of long side chains by short ones would give rise to the monomeric units with two different molecular figures, reducing the π-order. Moreover, the presence of short side chains might be advantageous to the building of π-interconnection due to the ease of steric repulsion. Fractional side-chain truncation could be a straightforward approach to regulating the proportion of π-order to π-interconnection.In this work, 2,6-dibromonaphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(2-octyldodecyl) diimide (Br-NDI2OD-Br), 2,6-dibromonaphthalene-1,4,5,8-tetracarboxylic-N,N′-bis(butyl) diimide (Br-NDIBu-Br), and 5,5′-bis(trimethylstannyl)-2,2′-bithiophene were copolymerized by the Stille polycondensation [11] ( Table 1). The fraction of Br-NDI2OD-Br to Br-NDIBu-Br was adjusted to give numerous co-polymers with various amounts of NDIBu moiety in the polymer chain. The electronic properties of the Conventional design principles toward conjugated polymers aiming at high organic field-effect-transistor (OFET) mobilities are directed at the establishment of extensive edge-on π-order. However, emerging principles state that efficient charge transport can be established through interconnected short-range-order polymer crystallites. Fractional side-chain truncation has been employed to furnish numerous polymers. The electronic structures of th...

Molecular and Energetic Order Dominate the Photocurrent Generation Process in Organic Solar Cells with Small Energetic Offsets

“…Both of them probably influence the charge separation and transport by forming morphological defects and traps. Recently, Lai et al found that the π-interconnection (sporadic packing) rather than the π-order of conjugated polymer can effectively promote charge transport, which could support our hypothesis favorably. Therefore, it is desirable to uncover the effect of molecular packing on the photoelectric conversion process in the PM7/N2200 bilayer devices.…”

Regulate the Electron Mobility and Threshold Voltage of P(NDI2OD‐T2)‐Based Organic Field‐Effect Transistors by the Compatibility Principle

“…The µ e 's of pristine P are comparable to the reported values. [ 36,39 ] However, the µ e of M was beyond the detecting limit in the as‐spun film or exceedingly low after thermal annealing, which is ascribed to the poor connectivity in the thin film, as observed in Figure 4p. Figure 5a reveals that in the as‐spun films, the µ e generally rose as the ratio of M increased in the blend.…”

“…P(NDI2OD‐T2) ( M n = 142 kDa, Đ = 3.1) which was prepared on the basis of our previous synthetic protocol is denoted as P in the following for convenience. [ 39 ] Synthesis of M is described in Scheme 1. Deprotonation of 2,2′‐bithiophene (1) by n ‐butyllithium gave a lithiated intermediate, which was treated with trimethyltin chloride to afford 5‐trimethylstannyl‐2,2′‐bithiophene (2).…”

“…Pristine P exhibited homogeneous fibrous structure (Figure 4a,h) as reported elsewhere. [ 8,29,39,61 ] Figure 4h reveals that after thermal annealing, surface fibers became more perceptible. Texture of M was yet lumpy, showing aggregated chunks (Figure 4g,n).…”

“…[ 36–38 ] π‐Stacking of the resultant polymers can be regulated and a decent electron mobility ( µ e ) of 0.31 cm 2 V −1 s −1 was achieved. [ 39 ] It is envisaged that the molecule stacking is associated with the compatibility. Strong stacking tendency between two components should encourage their compatibility, and vice versa.…”