Benzobisthiazole Polymer with Resonance-assisted Hydrogen Bonds for High-performance Transistor and Solar Cell Applications

Benzobisthiazole polymer with resonance-assisted hydrogen bonds(RAHBs)has been synthesized for both organic field-effect transistor and polymer solar cell applications.The properties of the hydrogen bonded polymer are compared with the reference polymer without RAHBs.Single-crystal X-ray diffraction analyses of the building block reveal that the RAHB interactions are formed between the carbamate hydrogen and imine nitrogen of the thiazoles.The hydrogen donor and acceptor are connected byπ-conjugated molecular framework and the hydrogen-bridged quasi aromatic rings lock the conformation of the building block.The building block adopted a layered sandwich packing in crystal instead of slipped herringbone stacking which was often found in the crystal of benzobisthiazole derivatives.The polymer PCBTZ-TT with RAHBs showed deeper HOMO/LUMO energy level(about 0.2 eV)than reference polymer.The PCBTZ-TT demonstrated the hole mobility of0.96 cm^(2)·V^(-1)·s^(-1) in field-effect transistor devices and achieved power conversion efficiency of 13.6%in solar cell devices with Y6 as acceptor without any additive.

The role of halogen bonding in improving OFET performance of a naphthalenediimide derivative

Controlling microstructure and thin film morphology of organic semiconductors by supramolecular arrangement is critical to improving their device performance. To realize well-controlling supramolecular assembly, a core-expanded naphthalene diimides derivative （1） was designed and synthesized as an n-type organic semiconductor and also as a halogen bonding （XB） donor that could form complementary XBs with 2,2-dipyridine or 2,2-bipyrimidine acceptor. The XB interactions in the solid state of 1/2,2- dipyridine and 1/2,2-bipyrimidine were confirmed by a series of characterization methods, such as thermal gravimetric analysis （TGA）, X-ray photoelectron spectroscopy （XPS）, nuclear magnetic resonance （NMR） involving 13F NMR and solid-state 13C NMR. Organic field-effect transistors （OFETs） based on XB complexes 1/2,2-dipyridine or 1/2,2-bipyrimidine showed better device performance than that of devices based on pure 1, with the average electron mobility increased more than doubled （from 0.027cm2V-1 s-1 to 0.070cm2V-1 s-1）.

Fine-tuning the molecular energy levels by incorporating thiophene units onto the π-backbone of core-expanded naphthalene diimides

A series of core-expanded naphthalene diimides（NDI-DTYM） and thiophene-based derivatives（1a-c）were designed and synthesized to investigate the relationship between molecular structures and the highest occupied molecular orbital（HOMO） energy levels but has little impact on the lowest unoccupied molecular orbital（LUMO） energy levels.The results demonstrated that increasing the number of thiophene units can gradually elevate the HOMO energy levels but had little impact on the LUMO energy levels.The n-channel organic field-effect transistors（OFETs） based on 1b and 1c have demonstrated that these almost unchanged LUMO energy levels are proper to transport electrons.

1,2,5,6-Naphthalenediimide-based Conjugated Copolymers Linked by Ethynyl Units

Two copolymers of P1 and P2 comprising benzothiadiazole, 1,4-bis（dodecyloxy）-benzene units were synthesized by Sonogashira coupling polymerization based on ethynyl-linked 1,2,5,6-naphthalenediimide. Their thermal, optical, electrochemical as well as charge transport properties were studied. Bottom-gate top-contact organic field-effect transistors （OFETs） measurements of P1 and P2 thin films showed different charge transport behaviors. P1 displayed pure electron transport behaviors in OFETs with electron mobility up to 10^-3 cm^2·V-1·s^-1, while P2 exhibited hole transport features. The molecular structure analysis revealed that the structure of P1 has the acceptor-linker-acceptor＇ （A-L-A＇） characteristic, and P2 possesses the donor-linker-acceptor （D-L-A） structure feature. The results demonstrate that different molecular structures lead them to have distinct charge transport behaviors. In particular, the first pure electron transport copolymer in OFETs based on 1,2,5,6-naphthalenediimide is achieved.