Recent Advances of Furan and Its Derivatives Based Semiconductor Materials for Organic Photovoltaics

The state-of-the-art bulk-heterojunction (BHJ)-type organic solar cells (OSCs) have exhibited power conversion efficiencies (PCEs) of exceeding 18%. Thereinto, thiophene and its fused-ring derivatives play significant roles in facilitating the development of OSCs due to their excellent semiconducting natures. Furan as thiophene analogue, is a ubiquitous motif in naturally occurring organic compounds. Driven by the advantages of furan, such as less steric hindrance, good solubility, excellent stacking, strong rigidity and fluorescence, biomass derived fractions, more and more research groups focus on the furan-based materials for using in OSCs in the past decade. To systematically understand the developments of furan-based photovoltaic materials, the relationships between the molecular structures, optoelectronic properties, and photovoltaic performances for the furan-based semiconductor materials including single furan, benzofuran, benzodifuran (BDF) (containing thienobenzofuran (TBF)), naphthodifurans (NDF), and polycyclic furan are summarized. Finally, the empirical regularities and perspectives of the development of this kind of new organic semiconductor materials are extracted.

Flexible, Low-Voltage, and n-Type Infrared Organic Phototransistors with Enhanced Photosensitivity via Interface Trapping Effect

Flexible and low-voltage near-infrared organic phototransistors (NIR OPTs) were prepared with a low-band gap donor-acceptor conjugated polymer as the semiconductor layer and n-octadecyl phosphonic acid modified anodic alumina (AlO _x/ODPA) as the insulating layer. The phototransistors exhibit the typical n-type transistor characteristics at a voltage below 5 V. The photosensitivity of phototransistors can be enhanced by regulating the packing densities of the ODPA self-assembled monolayers and forming different trap states. The enhanced OPTs exhibit good photosensitivity to 808-980 nm NIR with the photocurrent/dark current ratio and photoresponsivity as high as 5 × 10³ and 20 mA W^-1, respectively, benefiting from the charge-trapping effect at the AlO _x/ODPA interface. The OPTs also present a fast optical switching speed of 20/30 ms and an excellent mechanical flexibility. The outstanding performance of the NIR OPTs indicates that the development of wearable electronics is, indeed, possible.

Synthesis and Field-Effect Transistor Application of π-Extended Lactam-Fused Conjugated Oligomers obtained by Tandem Direct Arylation

Five π-extended lactam-fused conjugated oligomers (5FO, 5FS, 4FPO, 4FPS, and R-4FPO) were synthesized by the tandem direct arylation. The intermolecular oxidative direct arylation was applied in the second step. These conjugated oligomers had fine-tuned FMO energies predictable by the theoretical calculation and excellent thermal stabilities. 4FPO and 4FPS bearing tetrafluoropyridine exhibited lower LUMO energy levels (-3.20 eV and -3.39 eV, respectively) compared with others. Based on the X-ray crystallography, 4FPO was found to have a herringbone crystal packing and a considerably large electron transfer integral value (137 meV). 4FPO-based bottom-gate, bottom-contact FET device demonstrated an electron mobility of 5.2×10^-3  cm²  V^-1  s^-1 as a result of an edge-on alignment on the SiO₂ substrate.

Vinylene and benzo[c][1,2,5]thiadiazole: effect of the π-spacer unit on the properties of bis(2-oxoindolin-3-ylidene)-benzodifuran-dione containing polymers for n-channel organic field-effect transistors

Two polymers based on (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3H,7H)-dione (BIBDF) coupled with (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT) or dithienylbenzothiadiazole (TBT), namely PBIBDF-TVT and PBIBDF-TBT were synthesized via the Stille coupling reaction. The effect of benzothiadiazole or vinylene-π spacer of the copolymers on optical properties, energy levels, electronic device performance and microstructure were studied. It was found that PBIBDF-TBT based OFET devices, annealed at 180 °C, showed better performance with the highest electron mobility of 2.9 × 10⁻² cm² V s⁻¹ whereas PBIBDF-TVT polymer exhibited 5.0 × 10⁻⁴ cm² V s⁻¹. The two orders of magnitude higher electron mobility of PBIBDF-TBT over PBIBDT-TVT is a clear indicator of the better charge transport ability of this polymer semiconductor arising from its higher crystallinity and better donor–acceptor interaction.

Bottom-gate-top-contact OFET device structure using PBIBDF-TVT and PBIBDF-TBT based polymer semiconductors.

Facile green synthesis of isoindigo-based conjugated polymers using aldol polycondensation

A green and efficient synthetic protocol suitable for the preparation of isoindigo-based polymer was developed using aldol polymerization.

Bis(2-oxo-7-azaindolin-3-ylidene)benzodifuran-dione-based donor–acceptor polymers for high-performance n-type field-effect transistors

Two donor–acceptor (D–A) conjugated polymers were synthesized using a strongly electron-deficient unit as the acceptor, and dithiophene and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene as the donor units.

Enhanced near-infrared photoresponse of organic phototransistors based on single-component donor-acceptor conjugated polymer nanowires

Single-component near-infrared phototransistors based on ambipolar organic semiconductor nanowires have been investigated and compared with their corresponding thin-film counterparts. The nanowire organic phototransistors (NW-OPTs) showed photocurrent/dark-current ratios and photoresponsivities as high as 1.3 × 10(4) and 440 mA W(-1) for the p-type channel, and 3.3 × 10(4) and 70 mA W(-1) for the n-type channel, respectively, upon near-infrared illumination with an intensity of 47.1 mW cm(-2). These were much higher values compared to their thin-film counterparts. The enhancement of the near-infrared photoresponse could be attributed to the larger trap density originating from the semiconductor/insulator interface and the semiconductor/air interface. The performance of NW-OPTs was demonstrated to open up new possibilities to improve the near-infrared photoresponse of single-component devices.

Approaching high charge carrier mobility by alkylating both donor and acceptor units at the optimized position in conjugated polymers

A strategy for obtaining improved OFET mobility in both donor and acceptor alkylated polymer semiconductors.

Lactone-fused electron-deficient building blocks for n-type polymer field-effect transistors: synthesis, properties, and impact of alkyl substitution positions

Dilactone-based Pechmann dyes were incorporated into conjugated polymers for n-type field-effect transistors, providing a new design concept of electron-deficient building blocks for polymer semiconductors.

Benzothiophene-flanked diketopyrrolopyrrole polymers: impact of isomeric frameworks on carrier mobilities

The influence of isomeric backbones on field-effect properties in benzothiophene-flanked diketopyrrolopyrrole polymers was investigated.

A new thieno-isoindigo derivative-based D–A polymer with very low bandgap for high-performance ambipolar organic thin-film transistors

A new thieno-isoindigo derivative was synthesized by replacing the outer benzene ring of the isoindigo derivative (BIBDF) with thiophene.