Benzimidazolone-Dioxazine Pigments-Based Conjugated Polymers for Organic Field-Effect Transistor

Molecules based on benzimidazolone-dioxazine are known as blue/violet pigments and have been commercialized for decades. However, unfavorable solubility limits the application of these structures as building blocks of conjugated polymers despite their low band gaps. Herein, a series of donor-acceptor conjugated polymers containing soluble benzimidazolone-dioxazine structures as the acceptors and oligothiophene as donors are synthesized and investigated. With increasing numbers of thiophene rings, the steric hindrance diminishes and high molecular weight polymers can be achieved, leading to an improved performance in organic field effect transistor devices. The hole mobility of polymers with three to six thiophene units is in the order of 10^-1 cm² V^-1 s ^-1 . Among all the polymers, polymer P3 with three thiophene units between benzimidazolone-dioxazine structures shows the best hole mobility of 0.4 cm² V^-1 s ^-1 . Grazing-incidence wide-angle X-ray scattering results reveal that the high mobility of organic field-effect transistors (OFETs) can be accredited by matched donor-acceptor packing in the solid thin films.

Origin of Photovoltaics in Organic Solar Cells at Negligible Energy Level Offsets─An Insight of the Charge Accumulation Effect

Reducing the energy level offset is one of the key elements of low open-circuit voltage loss in organic solar cells. However, the origin of charge separation driving force at negligible energy level offsets still remains unexplained. Herein, from the perspective of built-in potential caused by charge accumulation, we discuss the nonequilibrium energy level displacement as current passing with distinct variable current densities. Due to the different carrier mobilities of electrons and holes in organic semiconductor materials, carriers with high mobility will be rapidly transmitted to the electrode, while those with low mobility will remain in the materials, resulting in the accumulation of corresponding charges. It is suggested that the higher the carrier mobility, the better the efficiency of photovoltaic devices, with the balance of the charge transport.

Recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells

Organic semiconductor materials, especially donor-acceptor (D-A) polymers, have been increasingly applied in organic optoelectronic devices, such as organic field-effect transistors (OFETs) and organic solar cells (OSCs). Plenty of high-performance OFETs and OSCs have been achieved based on varieties of structurally modified D-A polymers. As the basic building block of D-A polymers, acceptor moieties have drawn much attention. Among the numerous types, lactam- and imide-functionalized electron-deficient building blocks have been widely investigated. In this review, the structural evolution of lactam- or imide-containing acceptors (for instance, diketopyrrolopyrrole, isoindigo, naphthalene diimide, and perylene diimide) is covered and their representative polymers applied in OFETs and OSCs are also discussed, with a focus on the effect of varied structurally modified acceptor moieties on the physicochemical and photoelectrical properties of polymers. Additionally, this review discusses the current issues that need to be settled down and the further development of new types of acceptors. It is hoped that this review could help design new electron-deficient building blocks, find a more valid method to modify already reported acceptor units, and achieve high-performance semiconductor materials eventually.

Diketopyrrolopyrrole Based Organic Semiconductor Materials for Field-Effect Transistors

Over the past several decades, organic conjugated materials as semiconductors in organic field effect transistors (OFETs) have attracted more and more attention from the scientific community due to their intriguing properties of mechanical flexibility and solution processability. However, the device fabrication technique, design, and synthesis of novel organic semiconductor materials with high charge carrier mobility is crucial for the development of high-performance OFETs. In the past few years, more and more novel materials were designed and tested in the OFETs. Among which, diketopyrrolopyrrole (DPP) and its derivatives, as the electron acceptors to build donor-acceptor (D-A) typed materials, are the perspective. In this article, recently reported molecules regarding the DPP and its derivatives for OFETs application are reviewed. In addition, the relationship between the chemical structures and the performance of the device are discussed. Furthermore, an outlook of DPP-based materials in OFETs with a future design concept and the development trend are provided.

Benzo/Naphthodifuranone-Based Polymers: Effect of Perpendicular-Extended Main Chain π-Conjugation on Organic Field-Effect Transistor Performances

For polymer semiconductors, the backbone structure plays an essential role in determining their physicochemical properties and charge transport behaviors. In this work, two donor-acceptor-type polymers (P-BDF and P-NDF) based on benzodifuranone (BDF) and naphthodifunarone (NDF) as electron-deficient moieties and indaceno-dithiophene as electron-rich groups are designed, synthesized and, for the first time, applied in organic field-effect transistor. P-BDF and P-NDF differ from their backbone structures while P-BDF has a more planar backbone conformation due to its smaller conjugated core size and P-NDF features a perpendicular-extended main chain structure. As a result, P-BDF polymer exhibits bathochromic optical absorption, deeper molecular orbital energy levels, and more importantly, closer π-stacking and stronger aggregation in the solid state and thus affords a more promising hole mobility of up to 0.85 cm² V^-1 s^-1 in OFET devices, while that of the P-NDF-based devices is only 0.55 cm² V^-1 s^-1 . The results suggest the great potential of BDF/NDF-type chromophores in constructing novel organic semiconductors and also indicate that the main chain coplanarity of polymer semiconductors is more essential than the sole extension of π-conjugations (especially at the perpendicular direction of polymer main chains) for the design of high-performance OFET materials.

Long-range donor-acceptor electron transport mediated by α helices

We study the long-range electron and energy transfer mediated by a polaron on an α-helix polypeptide chain coupled to donor and acceptor molecules at opposite ends of the chain. We show that for specific parameters of the system, an electron initially located on the donor can tunnel onto the α helix, forming a polaron, which then travels to the other extremity of the polypeptide chain, where it is captured by the acceptor. We consider three families of couplings between the donor, the acceptor, and the chain and show that one of them can lead to a 90% efficiency of the electron transport from donor to acceptor. We also show that this process remains stable at physiological temperatures in the presence of thermal fluctuations in the system.

Conjugated Polymers Containing Building Blocks 1,3,4,6-Tetraarylpyrrolo[3,2-b]pyrrole-2,5-dione (isoDPP), Benzodipyrrolidone (BDP) or Naphthodipyrrolidone (NDP): A Review

π-Conjugated organic donor-acceptor (D-A) type polymers are widely developed and used in electronic device. Among which, diketopyrrolopyrrole (DPP)-based polymers have received the most attention due to their high performances. The novel chromophores named 1,3,4,6-tetraarylpyrrolo[3,2-b]pyrrole-2,5-dione (isoDPP), benzodipyrrolidone (BDP) and naphthodipyrrolidone (NDP) are resemble DPP in chemical structure. IsoDPP is an isomer of DPP, with the switching position of carbonyl and amide units. The cores of BDP and NDP are tri- and tetracyclic, whereas isoDPP is bicyclic. π-Conjugation extension could result polymers with distinct optical, electrochemical and device performance. It is expected that the polymers containing these high-performance electron-deficient pigments are potential in the electronic device applications, and have the potential to be better than the DPP-based ones. IsoDPP, BDP, and NDP based polymers are synthesized since 2011, and have not receive desirable attention. In this work, the synthesis, properties (optical and electrochemical characteristics), electronic device as well as their relationship depending on core-extension or structure subtle optimization have been reviewed. The final goal is to outline a theoretical scaffold for the design the D-A type conjugated polymers, which is potential for high-performance electronic devices.

Centrosymmetric Thiophenemethyleneoxindole-Based Donor-Acceptor Copolymers for Organic Field-Effect Transistors

Two novel, donor-acceptor-type π-conjugated polymers (P1 and P2) with 3'-(thieno[3,2-b]thiophene-2,5-diylbis(methan-1-yl-1-ylidene))bis-(indolin-2-one) (ITTI) as the acceptor and thiophene/bithiophene as the donor are designed and synthesized by palladium-catalyzed Stille coupling. The optical and electrochemical properties of these polymers are characterized and further implemented into organic field-effect transistors (OFET). Both polymers exhibit excellent thermal stability, broad UV-vis absorption, and high highest occupied molecular orbital energy levels. Thermal annealing induces a well-ordered structure, a highly planar π-system (oxygen-sulfur interaction), and a bathochromic shift in the polymers; furthermore, significant enhancement of the long wavelength intensity is also observed. Both polymers exhibit p-type charge transport behavior, with hole mobilities up to 0.51 cm² V^-1 s^-1 for P1 and 0.65 cm² V^-1 s^-1 for P2. This work demonstrates that ITTI can be a promising building block for the construction of donor-acceptor polymers with high-performance OFETs.

Thionating iso-diketopyrrolopyrrole-based polymers: from p-type to ambipolar field effect transistors with enhanced charge mobility

Two polymers based on isoDPP and isoDTPP were designed and synthesized. Thionation reactions could transform p-type polymers into ambipolar polymers for field effect transistors with enhanced charge mobility.