Yu-Qing Zheng

Towards rational design of organic electron acceptors for photovoltaics: a study based on perylenediimide derivatives

A series of PDI dimers featuring various arylene linkers are developed as electron acceptors in organic solar cells. Using P3HT as the donor, power conversion efficiency of up to 2.3% is achieved with two PDI dimers having spirobifluorene linkers. The results indicate that such non-planar, three-dimensional structures effectively suppress self-aggregation and crystallization of the PDI units, which is favourable for their solar cell performance.

Non-fullerene acceptors containing fluoranthene-fused imides for solution-processed inverted organic solar cells

Six fluoranthene-fused imide derivatives were employed as acceptors in solution processed inverted BHJ solar cells with P3HT as the donor. The PCEs of all devices vary from 2.14% to 2.89%. All acceptors are in their amorphous state with low electron mobility, but achieving high PCEs.

New polymer acceptors for organic solar cells: the effect of regio-regularity and device configuration

Two polymers, r-PDI-diTh and i-PDI-diTh, were synthesized as acceptors applicable for solution-processed BHJ OSCs. By introducing a bulky, dove tailed side chain and thereby suppressing the π–π interactions between perylenediimide units in the backbones of acceptor polymers, more effective phase segregation of these acceptors with a donor polymer (P3HT) was realized. By employing the inverted device configuration to better match the vertical phase separation of donor–acceptor polymers produced by solution processing, undesirable polaron pair recombination was suppressed, and PCE up to 2.17% was achieved from the regio-regular acceptor r-PDI-diTh.

Fine-Tuning of Crystal Packing and Charge Transport Properties of BDOPV Derivatives through Fluorine Substitution

Molecular packing in organic single crystals greatly influences their charge transport properties but can hardly be predicted and designed because of the complex intermolecular interactions. In this work, we have realized systematic fine-tuning of the single-crystal molecular packing of five benzodifurandione-based oligo(p-phenylenevinylene) (BDOPV)-based small molecules through incorporation of electronegative fluorine atoms on the BDOPV backbone. While these molecules all exhibit similar column stacking configurations in their single crystals, the intermolecular displacements and distances can be substantially modified by tuning of the amounts and/or the positions of the substituent fluorine atoms. Density functional theory calculations showed that the subtle differences in charge distribution or electrostatic potential induced by different fluorine substitutions play an important role in regulating the molecular packing of the BDOPV compounds. Consequently, the electronic couplings for electron transfer can vary from 71 meV in a slipped stack to 201 meV in a nearly cofacial antiparallel stack, leading to an increase in the electron mobility of the BDOPV derivatives from 2.6 to 12.6 cm(2) V(-1) s(-1). The electron mobility of the five molecules did not show a good correlation with the LUMO levels, indicating that the distinct difference in charge transport properties is a result of the molecular packing. Our work not only provides a series of high-electron-mobility organic semiconductors but also demonstrates that fluorination is an effective approach for fine-tuning of single-crystal packing modes beyond simply lowering the molecular energy levels.

Strong Electron‐Deficient Polymers Lead to High Electron Mobility in Air and Their Morphology‐Dependent Transport Behaviors

Planar backbone, locked conformation, and low lowest unoccupied molecular orbital level provide polymer F4 BDOPV-2T with ultrahigh electron mobilities of up to 14.9 cm(2) V(-1) s(-1) and good air stability. It is found that the nonlinear transfer curves can be tuned to near-ideal ones by changing fabrication conditions, indicating that film morphology largely contributes to the nonlinear transfer curves in high-mobility conjugated polymers.

A Cofacially Stacked Electron-Deficient Small Molecule with a High Electron Mobility of over 10 cm(2) V-1 s(-1) in Air

A strong, electron-deficient small molecule, F4 -BDOPV, has a lowest unoccupied molecular orbital (LUMO) level down to -4.44 eV and exhibits cofacial packing in single crystals. These features provide F4 -BDOPV with good ambient stability and large charge-transfer integrals for electrons, leading to a high electron mobility of up to 12.6 cm(2) V(-1) s(-1) in air.

Corannulene derivatives as non-fullerene acceptors in solution-processed bulk heterojunction solar cells

Corannulene derivatives were used in organic solar cells for the first time. Using Cor-PI and Cor-NI as acceptors, we achieved power conversion efficiencies up to 0.32% and 1.03%, suggesting potential applications of these fullerene segments as non-fullerene acceptors.

A corannulene-based donor–acceptor polymer for organic field-effect transistors

For the first time, the corannulene unit was incorporated directly into the backbone of conjugated polymers. A new donor–acceptor (D–A) copolymer PICBT using imide-fused corannulene as acceptor was synthesized and its performance in organic field-effect transistors (OFETs) was tested. PICBT exhibited ambipolar transporting property with a hole mobility of 0.025 cm2 V−1 s−1 and electron mobility of 7.45 × 10−5 cm2 V−1 s−1 when the substrates were treated with octyltrimethoxysilane (OTS). If the substrates were not modified with OTS, PICBT showed lower device performances with a hole mobility of 4.62 × 10−3 cm2 V−1 s−1 and electron mobility of 1.54 × 10−4 cm2 V−1 s−1. The device performances are competitive among the amorphous materials. This work paved the way for incorporating the corannulene unit into conjugated materials.

One-dimensional (1D) micro/nanostructures of organic semiconductors for field-effect transistors

Organic semiconductors have gradually become the super stars on the stage of optoelectronic materials, due to their low cost, flexibility and solution processability. Numerous organic semiconductors, including small molecules and conjugated polymers, have been designed and synthesized to explore the potential of organic materials in optoelectronic industry. One-dimensional micro/nanostructures of organic semiconductors generally have more ordered packing structure with fewer defects compared with thin films, and are thus thought to show intrinsic carrier mobility of organic materials. Moreover, the packing structure in micro/nanostructures is clear and relatively easy to analyze, which makes these micro/nanostructures a good platform to study structure-property relationship. Therefore, design of suitable organic molecules to form micro-/nanostructures and methods to obtain ideal micro/nanostructures for functional devices will be fully discussed in this mini review. Finally, the perspective and opportunity of 1D micro/nanostructured organic materials based OFETs in the near future are also addressed.

Synthesis, Properties, and Semiconducting Characteristics of BF2 Complexes of β,β-Bisphenanthrene-Fused Azadipyrromethenes

Three novel π-extended BF2 complexes of β,β-bisphenanthrene-fused azadipyrromethenes containing nine fused rings have been synthesized on the basis of a tandem Suzuki coupling reaction on readily available 2,6-dibromoazaBODIPYs followed by an intramolecular oxidative aromatic coupling mediated by iron(III) chloride. These resultant BF2 complexes exhibit strong absorption (extinction coefficients up to 2.4 × 105 M-1 cm-1) and emission in the near-infrared (NIR) range (790-816 nm) with excellent photo and thermal stabilities. The hole mobility of the thin-film field-effect transistors of these dyes fabricated by a solution process reaches up to 0.018 cm2 V-1 s-1.