N-Type Doping of Naphthalenediimide-Based Random Donor–Acceptor Copolymers to Enhance Transistor Performance and Structural Crystallinity

Abstract

An integrated strategy of molecular design and conjugated polymer doping is proposed to improve the electronic characteristics for organic field effect transistor (OFET) applications. Here, a series of soluble naphthalene diimide (NDI)-based random donor−acceptor copolymers with selenophene π-conjugated linkers and four acceptors with different electron-withdrawing strengths (named as rNDI-N/S/NN/SS) are synthesized, characterized, and used for OFETs. N-type doping of 5,6,12,12a,13,18,18a,19-octahydro-5,6-dimethyl-13,18[1′,2′]]benzodiazocine potassium triflate adduct (DMBI-BDZC) is successfully demonstrated. The undoped rNDI-N, rNDI-NN, and rNDI-SS samples exhibit ambipolar charge transport, while rNDI-S presents only a unipolar n-type characteristic. Doping with DMBI-BDZC significantly modulates the performance of rNDI-N/S OFETs, with a 3-to 6-fold increase in electron mobility (μ e ) for 1 wt % doped device due to simultaneous trap mitigation, lower contact resistance (R C ), and activation energy (E A ), and enhanced crystallinity and edge-on orientation for charge transport. However, the doping of intrinsic pro-quinoidal rNDI-NN/SS films exhibits unchanged or even reduced device performance. These findings allow us to manipulate the energy levels by developing conjugated copolymers based on various acceptors and quinoids and to optimize the dopant−polymer semiconductor interactions and their impacts on the film morphology and molecular orientation for enhanced charge transport.

Molecularly Engineered Quinoxaline-Pyridyl Pyrazine Polymers for Field-Effect Transistors and Complementary Circuits

“…Being able to tune the electronic and optical properties with electron-rich and electron-deficient units connected through a covalent linkage in donor–acceptor (D–A)-type copolymers has been very attractive for expanding the scope of low-cost electronic devices. − Not only do D–A copolymers help in reducing the optical band gap, which have excellent opportunities in photovoltaics, , having donor and acceptor chromophores in a polymer chain also enables both p-type and n-type transport. , Electron-deficient acceptor units such as benzothiadiazole (BT), benzotriazole (BTr), diketopyrrolopyrrole (DPP), isoindigo (IID), and naphthalenediimide (NDI) have received a lot of interest in organic electronics. DPP-based copolymers have been attractive in organic solar cells, photodetectors, and transistors due to their high carrier mobilities. − Replacing the sulfur atom with other heavier atoms offers a versatile approach for tailoring the electronic properties of materials and enhancing charge transport properties in IID-based copolymers. − NDI-type copolymers show great potential for doping and have found applications in various electronic devices, including thermoelectrics. − …”

Long-range polymer ordering by directional coating to remarkably enhance the charge carrier mobility in PCDTPT-based organic field-effect transistors

“…Such substantial enhancements in the performance of OFETs have enabled inspiring low-cost applications of flexible electronics like organic light emitting diodes, e-paper displays, chemical and biological sensors and RF identification tags. Among pi-conjugated polymers, donor-acceptor (D-A) copolymers are active in research owing to their high charge transport properties due to tight pi-pi stacking of alternate chains [3,[12][13][14][15]. These polymers are composed of donor and acceptor moieties where the strong interaction between the donor unit of one molecule and with acceptor unit of other molecule results in reduced intermolecular distance [16,17].…”

Designer Conjugation-Break Spacer That Boosts Charge Transport in Semiconducting Terpolymers

“…When employing a rigid moiety like DKPDO in CPs, it is important to address the trade-off between polymer solubility and molecular packing. − A facile and cost-effective strategy to address the dilemma is through a random terpolymerization approach by incorporating DKPDO as the third component into parent donor–acceptor CPs. This approach can lead to well-controlled optoelectronic properties, fine-tuned microstructures, as well as well-balanced interchain interactions and solubilities in those terpolymers. ,− In this study, incorporating DKPDO as a CBS into the CP backbone based on IID and bithiophene (2T) gives rise to a series of random terpolymers (Scheme d). Varying the DKPDO/IID ratio in the polymer backbone leads to a balanced control of optoelectronic properties, interchain aggregation, molecular packing, and solubility of those terpolymers.…”