Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-020288.pdf

A general relationship between disorder, aggregation and charge transport in conjugated polymers

The development of helicene molecules with significant chiroptical responses covering a broad range of the visible spectrum is highly desirable for chiral optoelectronic applications; however, their absorption dissymmetry factors (gabs) have been mostly lower than 0.01. In this work, we report unprecedented B,N-embedded double hetero[7]helicenes with nonbonded B and N atoms, which exhibit excellent chiroptical properties, such as strong chiroptical activities from 300 to 700 nm, record high gabs up to 0.033 in the visible spectral range, and tunable circularly polarized luminescence (CPL) from red to near-infrared regions (600-800 nm) with high photoluminescence quantum yields (PLQYs) up to 100%. As revealed by theoretical analyses, the high gabs values are related to the separate molecular orbital distributions owing to the incorporation of nonbonded B and N atoms. The new type of B,N-embedded double heterohelicenes opens up an appealing avenue to the future exploitation of high-performance chiroptical materials.

B,N-Embedded Double Hetero[7]helicenes with Strong Chiroptical Responses in the Visible Light Region.

High-efficiency organic solar cells (OSCs) largely rely on polymer donors. Herein, we report a new building block BNT and a relevant polymer PBNT-BDD featuring B-N covalent bond for application in OSCs. The BNT unit is synthesized in only 3 steps, leading to the facile synthesis of PBNT-BDD. When blended with a nonfullerene acceptor Y6-BO, PBNT-BDD afforded a power conversion efficiency (PCE) of 16.1 % in an OSC, comparable to the benzo[1,2-b:4,5-b']dithiophene (BDT)-based counterpart. The nonradiative recombination energy loss of 0.19 eV was afforded by PBNT-BDD. PBNT-BDD also exhibited weak crystallinity and appropriate miscibility with Y6-BO, benefitting of morphological stability. The singlet-triplet gap (ΔEST ) of PBNT-BDD is as low as 0.15 eV, which is much lower than those of common organic semiconductors (≥0.6 eV). As a result, the triplet state of PBNT-BDD is higher than the charge transfer (CT) state, which would suppress the recombination via triplet state effectively.

A Facile Synthesized Polymer Featuring B‐N Covalent Bond and Small Singlet‐Triplet Gap for High‐Performance Organic Solar Cells

A highly modular synthesis of BNB- and BOB-doped phenalenyls is presented. Treatment of the 1,8-naphthalenediyl-bridged boronic acid anhydride 1 with LiAlH4/Me3SiCl afforded the corresponding 1,8-n...

BNB-Doped Phenalenyls: Modular Synthesis, Optoelectronic Properties, and One-Electron Reduction.

Block copolymer thin films

Considerable efforts have been devoted to achieving stable acene derivatives for electronic applications; however, the instability is still a major issue for such derivatives. To achieve higher stability with minimum structural change, CC units in the acenes were replaced with isoelectronic BN units to produce a novel BN-embedded tetrabenzopentacene (BNTBP). BNTBP, with a planar structure, is highly stable to air, moisture, light, and heat. Compared with its carbon analogue tetrabenzopentacene (TBP), BN embedment lowered the highest occupied molecular orbital (HOMO) energy level of BNTBP, changed the orbital distribution, and decreased the HOMO orbital coefficients at the central carbon atoms, which stabilize BNTBP molecules upon exposure to oxygen and sunlight. The single-crystal microribbons of BNTBP exhibited good performance in field-effect transistors (FETs). The high stability and good mobility of BNTBP indicates that BN incorporation is an effective approach to afford stable large-sized acenes with desired properties.

BN‐Embedded Tetrabenzopentacene: A Pentacene Derivative with Improved Stability

Directed self-assembly of block copolymers is a key enabler for nanofabrication of devices with sub-10 nm feature sizes, allowing patterning far below the resolution limit of conventional photolithography. Among all the process steps involved in block copolymer self-assembly, solvent annealing plays a dominant role in determining the film morphology and pattern quality, yet the interplay of the multiple parameters during solvent annealing, including the initial thickness, swelling, time, and solvent ratio, makes it difficult to predict and control the resultant self-assembled pattern. Here, machine learning tools are applied to analyze the solvent annealing process and predict the effect of process parameters on morphology and defectivity. Two neural networks are constructed and trained, yielding accurate prediction of the final morphology in agreement with experimental data. A ridge regression model is constructed to identify the critical parameters that determine the quality of line/space patterns. These results illustrate the potential of machine learning to inform nanomanufacturing processes.

Machine Learning Predictions of Block Copolymer Self-Assembly.

Highly ordered nanostructures assembled from conjugated polymers have great potential for probing fundamental structure-property relationships, as well as boosting the charge transport performance. To date, the effect of solution-state aggregation on crystallization and charge transport in conjugated polymers is still unclear and in need of precise description at the molecular level. In this work, we report a systematic study of solution-state aggregation on crystallization and charge transport in BDOPV-based conjugated polymers through side chain engineering. Detailed analysis of crystal packing structures of conjugated polymers reveals that intermolecular displacements are substantially modified in order to minimize steric hindrance caused by the alkyl side chains. Moreover, subtle differences in side chain chemical structures play a vital role in regulating solution-state aggregation, and thus crystalline domain sizes in both microwires and thin films. Farther branched side chain leads to larger polymer aggregates in solution and therefore larger crystalline domains in solid films. Subsequently, an increase in electron mobility is obtained with the highest mobility values surpassing 10 cm2 V−1 s−1. This work unravels that the modification of the side chains is an efficient strategy for fine-tuning the interchain organization of conjugated polymers from solution to solid state.

Influence of solution-state aggregation on conjugated polymer crystallization in thin films and microwire crystals

BN Fused Diazulenyl‐Carbazole: Synthesis, Structure, and Properties

The Diels–Alder reaction strategy that can rapidly extend the conjugated backbone was applied to facilely synthesize fold-line, coplanar BN-embedded polycyclic aromatic hydrocarbons from simple sma...

Ze-Hao Sun

Papers

BN‐Embedded Tetrabenzopentacene: A Pentacene Derivative with Improved Stability

Machine Learning Predictions of Block Copolymer Self-Assembly.

Influence of solution-state aggregation on conjugated polymer crystallization in thin films and microwire crystals

BN Fused Diazulenyl‐Carbazole: Synthesis, Structure, and Properties

Rapid Construction of Fold-Line-Shaped BN-Embedded Polycyclic Aromatic Compounds through Diels-Alder Reaction.