Effects of π-Conjugated Bridges on Photovoltaic Properties of Donor-π-Acceptor Conjugated Copolymers

(E)-1,2-Di(thiophen-2-yl)ethene based high mobility polymer for efficient photovoltaic devices without any post treatment

The ethene based polymer shows better photovoltaic performance.

Synthesis of alternating D–A1–D–A2 terpolymers comprising two electron-deficient moieties, quinoxaline and benzothiadiazole units for photovoltaic applications

Two new regular (D–A1–D–A2) terpolymersP1andP2containing two electron-deficient moieties, quinoxaline and benzothiadiazole, were designed and synthesized.

Effect of fluorination and symmetry on the properties of polymeric photovoltaic materials based on an asymmetric building block

Introducing fluorine on benzothiadiazole unit significantly influenced the properties of DTPa and BTs based conjugated polymers by tuning the energy levels and symmetry of the building blocks.

Benzobisthiadiazole-alt-bithiazole copolymers with deep HOMO levels for good-performance field-effect transistors with air stability and a high on/off ratio

Two benzobisthiadiazole-alt-bithiazole copolymers were designed and synthesized, and the resulting transistors achieved high performance with air stability and a high on/off ratio.

Medium Bandgap Conjugated Polymer for High Performance Polymer Solar Cells Exceeding 9% Power Conversion Efficiency

Two medium-bandgap polymers composed of benzo[1,2-b:4,5-b']dithiohpene and 2,1,3-benzothiadiazole with 6-octyl-thieno[3,2-b]thiophene as a π-bridge unit are synthesized and their photovoltaic properties are analyzed. The two polymers have deep highest occupied molecular orbital energy levels, high crystallinity, optimal bulk-heterojunction morphology, and efficient charge transport, resulting in a power conversion efficiency of as high as 9.44% for a single-junction polymer solar-cell device.

Effect of fluorine substitution on the photovoltaic performance of poly(thiophene-quinoxaline) copolymers

Three new conjugated polymers with or without fluorine substituents on quinoxaline ring were investigated in detail to assess the role of F in OPV performance.

4,7-Di-2-thienyl-2,1,3-benzothiadiazole with hexylthiophene side chains and a benzodithiophene based copolymer for efficient organic solar cells

A hexylthiophene side chain can induce conformational torsion a polymer with a BDT-DTBT backbone. HighV_ocand PCE polymer solar cells can be achieved.

Direct C–H arylation synthesis of (DD′AD′DA′)-constituted alternating polymers with low bandgaps and their photovoltaic performance

The alternating copolymers possess a planar backbone structure and high intramolecular charge transfer, and they contain a strong push–pull (D–A) system and gave a power conversion efficiency up to 2.36%.

An Alternating Donor–Acceptor Conjugated Polymer Based on Benzodithiophene and [3,4-c]pyrrole-4,6-dione: Synthesis, Characterization, and Application in Photovoltaic Devices

The synthesis is described of a new alternating donor–acceptor semiconducting polymer based on an N-octylthieno[3,4-c]pyrrole-4,6-dione building block together with a newly designed 2,3-bis(2-ethylhexyl)thiophenylethynyl substituted benzodithiophene (BDT). The introduction of electron-rich thiophene units to BDT raises the highest occupied molecular orbital (HOMO) level of the conjugated polymer and the concomitant reduction of the bandgap enhances the harvesting of solar radiation. This modification also introduces less sterically demanding triple bonds, thereby potentially enabling more favourable molecular interactions and an extra dimension of conjugation perpendicular to the main polymer chain. The optoelectronic properties of this new conjugated polymer were evaluated using UV-visible absorption and fluorescence spectroscopy, photoelectron spectroscopy in air, photo-induced charge extraction by linearly increasing voltage (Photo-CELIV), and density functional theory calculations. The polymer absorbs broadly in the wavelength range 300–700 nm in solution and the solid state. The estimated HOMO and LUMO levels of −5.4 and −3.6 eV, respectively, correspond to a bandgap of 1.8 eV. Photovoltaic devices fabricated using the polymer as the active layer displayed power conversion efficiencies (PCEs) of up to 1 %. Photo-CELIV results provide evidence that rapid recombination and poor charge mobility are likely contributing factors to the relatively low PCE values observed.

Synthesis of conjugated polymers via an exclusive direct-arylation coupling reaction: a facile and straightforward way to synthesize thiophene-flanked benzothiadiazole derivatives and their copolymers

Thiophene-flanked benzothiadiazole derivatives and their copolymers were synthesized via exclusive direct-arylation coupling reactions.

Theoretical studies on the effect of a bithiophene bridge with different substituent groups (R = H, CH3, OCH3 and CN) in donor–π–acceptor copolymers for organic solar cell applications

The design of a series of D–π–A copolymers.

Dithieno[3,2-b:2′,3′-d]silole-based low band gap polymers: the effect of fluorine and side chain substituents on photovoltaic performance

The effect of the F atom and the side-chain of dithieno[3,2-b:2′,3′-d]silole-based polymers on the optical, carrier mobility and photovoltaic properties was investigated.

Correlation of structure and photovoltaic performance of benzo[1,2-b:4,5-b′]dithiophene copolymers alternating with different acceptors

The PBDTT–TTz/PC₆₁BM (1 : 2) devices with PFN as the cathode interfacial layer delivered a power conversion efficiency of 2.60% for polymer solar cells.

Amorphous thieno[3,2-b]thiophene and benzothiadiazole based copolymers for organic photovoltaics

Three types of amorphous thienothiophene (TT)-benzothiadiazole (BT) based copolymers (PFTTBT) were synthesized by incorporating alkyl-substituted fluorene moieties as a third component in the polymer backbone. Their optical, electrochemical, morphological, and photovoltaic properties were examined by a comparison with those of a crystalline TT-BT derivative (PTTBT14). PTTBT14 was reported to have a high hole mobility (0.26 cm(2)/(V s)) due to the pronounced interchain ordering but poor photovoltaic power conversion efficiency (PCE) of 2.4-2.6% was reported due to excessively strong self-interactions with poor miscibility with fullerene structures. By incorporating fluorene units, the UV-vis spectra showed an increased bandgap (∼1.9 eV) with the disappearance of the packing-originated shoulder peak, and the valence band decreased compared to crystalline PTTBT14. The amorphous PFTTBT polymers showed substantially improved photovoltaic properties compared to PTTBT14, even though they showed poor hole mobility (∼10(-6) cm2/(V s)) and fill factor. The optimal devices were achieved by blending with excess PC71BM (polymer:PC71BM=1:4 by weight), showing little improvement in the thermal and additive treatments. Under simulated solar illumination of AM 1.5 G, the best PCE of 6.6% was achieved for a PFehTTBT:PC71BM device with an open-circuit voltage of 0.92 V, a short-circuit current of 15.1 mA/cm2, and a fill factor of 0.48. These results suggest that it is useful to disrupt partially the interchain organizations of excessively crystalline polymers, enabling fine-control of intermolecular ordering and the morphological properties (i.e., miscibility with fullerene derivatives, etc.) to utilize the advantages of both crystalline and amorphous materials for further improving PCE of polymer solar cells.

Effects of cyano (CN)-groups on the planarity, film morphology and photovoltaic performance of benzodithiophene-based polymers

A class of polymers (POT-DH, POT-HCN and POT-DCN) were synthesized and they contain the same donor (BDT) and acceptor units but different numbers of cyano (CN)-groups, i.e. 0, 1 and 2.

Synthesis of donor–acceptor conjugated polymers based on benzo[1,2-b:4,5-b′]dithiophene and 2,1,3-benzothiadiazole via direct arylation polycondensation: towards efficient C–H activation in nonpolar solvents

1,2-Dimethylbenzene, as a nonpolar high boiling point solvent, has been discovered to be a superior medium to perform direct-arylation polymerization.

Rational design on D–A conjugated P(BDT–DTBT) polymers for polymer solar cells

This review summarizes the various structural modifications and photovoltaic properties of the benzodithiophene–benzothiadiazole conjugated polymers [P(BDT–DTBT)] and their derivatives.