Two kinds of conjugated C3-symmetric perylene dyes, namely, triperylene hexaimides (TPH) and selenium-annulated triperylene hexaimides (TPH-Se), are efficiently synthesized. Both TPH and TPH-Se have broad and strong absorption in the region 300-600 nm together with suitable LUMO levels of about -3.8 eV. Single-crystal X-ray diffraction studies show that TPH displays an extremely twisted three-bladed propeller configuration and a unique 3D network assembly in which three PBI subunits in one TPH molecule have strong π-π intermolecular interactions with PBI subunits in neighboring molecules. The integration of selenophene to TPH endows TPH-Se with a more distorted propeller configuration and a more compact 3D network assembly due to the Se···O interactions. A single-crystal transistor confirms that both TPH and TPH-Se possess good electron-transport ability. TPH and TPH-Se acceptor-based solar cells show high power conversion efficiency of 8.28% and 9.28%, respectively, which mainly results from the combined properties of broad and strong absorption ability, appropriate LUMO level, desirable aggregation, high electron mobility, and good film morphology with the polymer donor.
The width of the interface between two immiscible polymers, deuterated polystyrene and poly(methyl methacrylate), has been measured using neutron reflectivity as a function of the thickness of the deuterated polystyrene layer. A logarithmic dependence of interface width on film thickness is observed, characteristic of an interface broadened by thermal induced capillary waves, whose spectrum is cut off by dispersive interactions across the polymer layer. Reasonable agreement is obtained with the results of self-consistent field theory when suitably modified to account for capillary waves, resolving a longstanding discrepancy between theory and experiment. [S0031-9007(97)03096-2]
A series of bay-linked perylene bisimides as non-fullerene acceptors for organic solar cells are designed. The best power conversion efficiency up to 3.63% based on s-diPBI (1b) is demonstrated by fine-tuning optoelectronic properties resulting from different degrees of twisting and flexibility by bay-linkages.
Newly designed asymmetric diketopyrrolopyrrole conjugated polymers with two different aromatic substituents possess a hole mobility of 12.5 cm(2) V(-1) s(-1) in field-effect transistors and a power conversion efficiency of 6.5% in polymer solar cells, when solution processed from a nonchlorinated toluene/diphenyl ether mixed solvent.
Arecordpower conversion efficiency of 8.40 %was obtained in single-component organic solar cells (SCOSCs) based on double-cable conjugated polymers.T his is realized based on exciton separation playing the same role as charge transport in SCOSCs.T wo double-cable conjugated polymers were designed with almost identical conjugated backbones and electron-withdrawing side units,b ut extra Cl atoms had different positions on the conjugated backbones.W hen Cl atoms were positioned at the main chains,the polymer formed the twist backbones,e nabling better miscibility with the naphthalene diimide side units.T his improves the interface contact between conjugated backbones and side units,resulting in efficient conversion of excitons into free charges.T hese findings reveal the importance of charge generation process in SCOSCs and suggest as trategy to improve this process: controlling miscibility between conjugated backbones and aromatic side units in double-cable conjugated polymers.
The copper-mediated Ullmann coupling of 1,7-dibromoperylene bisimides afforded structurally perfect singly-linked perylene bisimide (PBI) arrays, whilst the homo-coupling of 1,12-dibromoperylene bisimides gave doubly-linked and triply-linked diperylene bisimides. The interactions of three bay-linked diperylene bisimides that differed in their linkage (singly, doubly, and triply) were investigated in their neutral and reduced forms (mono-anion to tetra-anion). UV/Vis absorption and fluorescence spectroscopy revealed different degrees of interaction, which was explained by exciton coupling and conjugation effects. The electrochemical properties and spectroelectrochemistry also showed quite-different degrees of PBI interactions in the reduced mixed-valence species, which was apparent by the observation of CT bands. The interpretation of the experimental findings was supported by spin-restricted and -unrestricted DFT and time-dependent TD-DFT calculations with the long-range-corrected CAM-B3LYP functional. Accordingly, the degree of interaction in both the neutral and reduced forms of the bay-linked PBIs was qualitatively in the order doubly linked
Conspectus
Conjugated polymers for application in organic
solar cells (OSCs)
have been developed from poly(phenylenevinylene) to poly(3-hexylthiophene)
and then to “donor–acceptor” structures, providing
power conversion efficiencies (PCEs) over 18% when blending with the
electron acceptor as a two-component photoactive layer. Besides, graft-structural
double-cable conjugated polymers that use an electron donor as conjugated
backbones and an electron acceptor as pendant side units are one kind
of conjugated polymer, in which charge carriers are generated in a
single polymer. Therefore, double-cable conjugated polymers can be
used as a single photoactive layer in single-component OSCs (SCOSCs).
The covalently linked electron donor and acceptor enable double-cable
polymers to maintain stable microstructures during long-term operation
compared to two-component systems, which is very important for OSCs
toward large-area applications. However, SCOSCs based on double-cable
conjugated polymers provided PCEs below 3% in a long period, which
is lagging far behind PCEs of two-component OSCs. The key reason for
this is the limited number of chemical structures and the difficulty
to tune the morphology in these polymers.
In this Account, we
provide an overview about our efforts on developing
new double-cable conjugated polymers with rylene diimides as side
units, and how to realize high PCEs in SCOSC devices. The studies
start from developing a “functionalization–polymerization”
method to synthesize the polymers containing rylene diimide acceptors,
so that large amounts of double-cable conjugated polymers with distinct
physical and electrochemical properties were obtained. Then, we will
discuss how to control the nanophase separation in the crystalline
region and optimize the miscibility in the amorphous region of double-cable
polymers, simultaneously facilitating exciton dissociation and charge
transport. With these efforts, a high PCE of 8.4% has been obtained,
representing the record PCE in SCOSCs. In addition, the physical process
and the stability of SCOSCs will be discussed. We hope that this account
will inspire many innovative studies in this field and push the PCEs
of SCOSCs to a new stage.
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