Hongliang Zhong

Rigidifying Nonplanar Perylene Diimides by Ring Fusion Toward Geometry-Tunable Acceptors for High-Performance Fullerene-Free Solar Cells.

Rigid fused perylene diimide (PDI) dimers bridged with heterocycles exhibit superior photovoltaic performance compared to their unfused semiflexible analogues. Changing the chalcogen atoms in the aromatic bridges gradually increases the twist angles between the two PDI planes, leading to a varied morphology in which the one bridged by thiophene achieves a balance and shows the best efficiency of 6.72%.

Fused dithienogermolodithiophene low band gap polymers for high-performance organic solar cells without processing additives.

We report the synthesis of a novel ladder-type fused ring donor, dithienogermolodithiophene, in which two thieno[3,2-b]thiophene units are held coplanar by a bridging dialkyl germanium. Polymerization of this extended monomer with N-octylthienopyrrolodione by Stille polycondensation afforded a polymer, pDTTG-TPD, with an optical band gap of 1.75 eV combined with a high ionization potential. Bulk heterojunction solar cells based upon pDTTG-TPD:PC(71)BM blends afforded efficiencies up to 7.2% without the need for thermal annealing or processing additives.

Air‐Stable and High‐Mobility n‐Channel Organic Transistors Based on Small‐Molecule/Polymer Semiconducting Blends

Use of a carefully designed small-molecule organic semiconductor based on an oxidized diketopyrrolopyrrole core enables the fabrication by solution processing of electron-transporting (n-channel) blend-based organic thin-film transistors with high electron mobility (0.5 cm(2)/Vs) and high operating stability even when the devices are exposed to ambient air for prolonged periods of time.

Influence of Regio- and Chemoselectivity on the Properties of Fluoro-Substituted Thienothiophene and Benzodithiophene Copolymers

By studying the regio- and chemoselectivity of fluoro-substituted thienothiophene and benzodithiophene copolymers, we found polymers made from conventional one-pot polycondensation reaction consist of two distinctly different segments with a ratio of 0.36/0.64. Through further comparative studies of neat regioregular polymers based on each individual segment, we have identified the specific segment that contributes to the superior absorption, packing order, and charge mobility in the corresponding polymers. The unique structure-property relationships are the result of cooperative molecular arrangements of the key segment and noncovalent interaction between the fluoro group and the aromatic proton on the thiophene side-chain of the polymers.

Low band gap dithienogermolodithiophene copolymers with tunable acceptors and side-chains for organic solar cells

We report the synthesis and characterisation of five new donor–acceptor type co-polymers based on a fused dithienogermolodithiophene unit for use in photovoltaic devices. The influence of three electron deficient co-monomers, as well as the length and variety of the solubilising side-chains, on the physical and optoelectronic properties of the polymers is reported. The number and variety of alkyl side-chains is found to have a significant impact on the polymer aggregation and film morphology, with larger and more bulky side-chains leading to improved solubility and molecular weight. The influence of these properties upon the performance of bulk heterojunction solar cells is shown.

A regioregular conjugated polymer for high performance thick-film organic solar cells without processing additive

To address the challenges of reliability and facile processability of a benchmark polymer PTB7-Th, one of the most prevailing donor materials utilized in organic solar cells, we have systematically investigated the correlations among chemical structure, processing, morphology and device performance. Our study reveals that the regioregularity of PTB7-Th plays a crucial role in polymer properties as well as the fabrication process of devices. The regioregular polymer entirely consisting of favourable repeat units is capable of realizing high power conversion efficiency (>10%) in organic solar cells without using any solvent additive and tedious processing treatments. More importantly, the device efficiency based on this regioregular polymer is insensitive over a broad range of film thickness (from 100 nm to >400 nm). This will be very advantageous for manufacturing highly efficient and stable polymer solar cells by high throughput fabrication processes.

Long-lived, Non-Geminate, Radiative Recombination of Photogenerated Charges in a Polymer:Small-Molecule Acceptor Photovoltaic Blend

Minimization of open-circuit-voltage ( VOC) loss is required to transcend the efficiency limitations on the performance of organic photovoltaics (OPV). We study charge recombination in an OPV blend comprising a polymer donor with a small molecule nonfullerene acceptor that exhibits both high photovoltaic internal quantum efficiency and relatively high external electroluminescence quantum efficiency. Notably, this donor/acceptor blend, consisting of the donor polymer commonly referred to as PCE10 with a pseudoplanar small molecule acceptor (referred to as FIDTT-2PDI) exhibits relatively bright delayed photoluminescence on the microsecond time scale beyond that observed in the neat material. We study the photoluminescence decay kinetics of the blend in detail and conclude that this long-lived photoluminescence arises from radiative nongeminate recombination of charge carriers, which we propose occurs via a donor/acceptor CT state located close in energy to the singlet state of the polymer donor. Additionally, crystallographic and spectroscopic studies point toward low subgap disorder, which could be beneficial for low radiative and nonradiative losses. These results provide an important demonstration of photoluminescence due to nongeminate charge recombination in an efficient OPV blend, a key step in identifying new OPV materials and materials-screening criteria if OPV is to approach the theoretical limits to efficiency.