Branched Poly(thienylene vinylene)s with Absorption Spectra Covering the Whole Visible Region

Synthesis and Excited State Modulation of Organic Blue light Emitters Based on 2,4,6-Triphenyl-1,3,5-triazine and Carbazole Derivatives through ortho-Positioned Linking Models

Here, 9-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (OSTrPhCz) is used as a model emitter, and carbazole or 2-bromized carbazole are introduced into the ortho- positions of 2,4,6-triphenyl-1,3,5-triazine framework to generate two emitters, namely OTrPhCz and...

Transition-metal-free and halogen-free controlled synthesis of poly(3-alkylthienylene vinylene) via the Horner–Wadsworth–Emmons condensation reaction

Controlled polymerization without a transition metal or halogen.

Organic light-emitting diodes: theoretical understanding of highly efficient materials and development of computational methodology

Theoretical understanding of organic light-emitting diodes started from the quest to the nature of the primary excitation in organic molecular and polymeric materials. We found the electron correlation strength, bond-length alternation as well as the conjugation extent have strong influences on the orderings of the lowest lying excited states through the first application of density matrix renormalization group theory to quantum chemistry. The electro-injected free carriers (with spin 1/2) can form both singlet and triplet bound states. We found that the singlet exciton formation ratio can exceed the conventional 25% spin statistics limit. We proposed a vibration correlation function formalism to evaluate the excited-state decay rates, which is shown to not only give reasonable estimations for the quantum efficiency but also a quantitative account for the aggregation-induced emission (AIE). It is suggested to unravel the AIE mechanism through resonance Raman spectroscopy.

Modified structure of two-dimensional polythiophene derivatives by incorporating electron-deficient units into terthiophene-vinylene conjugated side chains and the polymer backbone: synthesis, optoelectronic and self-assembly properties, and photovoltaic application

Molecular engineering on the conjugated side chains of two-dimensional (2D) conjugated polymers was conducted and its effect on the optical, electronic, self-assembly and photovoltaic properties was investigated.

Synthesis and Characterization of Poly(selenylene vinylene) and Poly(selenylene vinylene)-co-Poly(thienylene vinylene) through Acyclic Diene Metathesis (ADMET) Polymerization

We report the synthesis and characterization of poly(3-decylselenylene vinylene) (P3DSV) homopolymers and poly(3-decylselenylene vinylene)-co-poly(3-decylthienylene vinylene) (P3DSV-co-P3DTV) copolymers through acyclic diene metathesis (ADMET) polymerization techniques. The obtained polymers were fully characterized. P3DSV was found to possess reduced crystallinity and a smaller bandgap of about 1.6 eV, compared with those of poly(3-decylthienylene vinylene) (P3DTV) analogs. P3DSV-co-P3DTV shows electronic properties between those of the corresponding homopolymers and distinctly different from those of simple blends of the two homopolymers. Our methodology provides a new way to control the physical and electronic properties of low bandgap poly(arylene vinylene)s (PAVs).

Single-junction polymer solar cells with over 10% efficiency by a novel two-dimensional donor-acceptor conjugated copolymer

Recent advances in bulk heterojunction (BHJ) polymer solar cell (PSC) performance have resulted from compressing the band gap to enhance the short-circuit current density (JSC) while lowering the highest occupied molecular orbital to increase the open-circuit voltage (VOC) and consequently enhance the power conversion efficiencies (PCEs). However, PCEs of PSCs are still constrained by a low JSC, small VOC, and low fill factor (FF). In this study, we report 10.12% PCE from single-junction PSCs based on a novel two-dimensional (2D) conjugated copolymer. By introduction of conjugated 5-alkylthiophene-2-yl side chains to substitute nonconjugated alkoxy side chains in one-dimensional (1D) poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), a novel 2D donor-acceptor low-band-gap conjugated copolymer, poly[[4,8-bis[(5-ethylhexyl)thienyl]benzo[1,2-b;3,3-b]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-DT), is developed. 2D PTB7-DT is further systematically investigated by absorption spectroscopy, cyclic voltammetry, charge carrier mobility measurement, thin film morphology, and wide-angle X-ray diffraction and compared with 1D PTB7. In comparison with 1D PTB7, 2D PTB7-DT possesses a narrower band gap, tighter π-π stacking, and higher charge carrier mobility. These results are consistent with the observation from first-principle calculations. Consequently, the single-junction PSCs based on 2D PTB7-DT exhibit a PCE of 10.12% with a high JSC, larger VOC, and high FF in comparison with the PSCs based on 1D PTB7.

Rhodanine dye-based small molecule acceptors for organic photovoltaic cells

Two small molecule acceptors, composed of carbazole or fluorene cores and rhodanine dye ends, were synthesized and their high OPV performances up to 3.08% were demonstrated.

Development of Low Energy Gap and Fully Regioregular Polythienylenevinylene Derivative

Low energy gap and fully regioregular conjugated polymers find its wide use in solar energy conversion applications. This paper will first briefly review this type of polymers and also report synthesis and characterization of a specific example new polymer, a low energy gap, fully regioregular, terminal functionalized, and processable conjugated polymer poly-(3-dodecyloxy-2,5-thienylene vinylene) or PDDTV. The polymer exhibited an optical energy gap of 1.46 eV based on the UV-vis-NIR absorption spectrum. The electrochemically measured highest occupied molecular orbital (HOMO) level is −4.79 eV, resulting in the lowest unoccupied molecular orbital (LUMO) level of −3.33 eV based on optical energy gap. The polymer was synthesized via Horner-Emmons condensation and is fairly soluble in common organic solvents such as tetrahydrofuran and chloroform with gentle heating. DSC showed two endothermic peaks at 67°C and 227°C that can be attributed to transitions between crystalline and liquid states. The polymer is thermally stable up to about 300°C. This polymer appears very promising for cost-effective solar cell applications.

Design of donors with broad absorption regions and suitable frontier molecular orbitals to match typical acceptors via substitution on oligo(thienylenevinylene) toward solar cells

A series of oligo(thienylenevinylene) derivatives with or without thieno[3,2-b]thiophene analogs as cores and three types substituent has been investigated at the PBE0/6-31G(d) and the TD-PBE0/6-31+G(d,p) levels to design materials with high performance such as suitable frontier molecular orbital (FMO) energies to match those of [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) and its derivatives, broad absorption spectra, higher and balance transfer property, and better stability. The results reveal that fused cores have slight effects on photophysical properties of investigated derivatives. The electron-withdrawing or push-pull substituents result in red shifts of absorption spectra and better stabilities for investigated derivatives. The calculated reorganization energies of designed derivatives suggest them to be good potential ambipolar transport materials under the proper operating conditions. The promising donors for PCBM, bisPCBM, PC70BM, and indene-C(60) bisadduct (ICBA) as acceptors are recommended theoretically for solar cells based on the proper match for FMOs between donors and acceptors. Moreover, we have also predicted the mobility of designed molecule with better performance.

EXCITON BINDING ENERGY OF ELECTRONIC POLYMERS: A FIRST PRINCIPLES STUDY

Exciton binding energy (E b ) is a key factor for the polymer electronics as well as for the fundamental polymer physics, which has been controversial since long time. Light-emitting polymer requires a large E b so that the charge recombination dominates. But, the photovoltaic polymers need small E b to allow efficient charge separation. First-principles Density Functional Theory (DFT) is employed to calculate E b for polydiacetylene (PDA), trans-polyacetylene (PA), polythiophene (PT), poly(2,5-thienylenevinylene) (PTV), and poly(p-phenylene vinylene) (PPV). We find that the hybrid B3LYP, B972, PBE1PBE, and B1B95 functionals with 20–25% amount of exact HF exchange can give reasonable results and predict E b is around 0.1–0.6 eV for these π-conjugated polymers.