Sifen Yang

Diketopyrrolopyrrole-based conjugated polymer entailing triethylene glycols as side chains with high thin-film charge mobility without post-treatments

Side chain engineering of conjugated donor–acceptor polymers is a new way to manipulate their optoelectronic properties. Two new diketopyrrolopyrrole (DPP)‐terthiophene‐based conjugated polymers PDPP3T‐1 and PDPP3T‐2, with both hydrophilic triethylene glycol (TEG) and hydrophobic alkyl chains, are reported. It is demonstrated that the incorporation of TEG chains has a significant effect on the interchain packing and thin‐film morphology with noticeable effect on charge transport. Polymer chains of PDPP3T‐1 in which TEG chains are uniformly distributed can self‐assemble spontaneously into a more ordered thin film. As a result, the thin film of PDPP3T‐1 exhibits high saturated hole mobility up to 2.6 cm2 V−1 s−1 without any post‐treatment. This is superior to those of PDPP3T with just alkyl chains and PDPP3T‐2. Moreover, the respective field effect transistors made of PDPP3T‐1 can be utilized for sensing ethanol vapor with high sensitivity (down to 100 ppb) and good selectivity.

Conjugated donor–acceptor terpolymers entailing the Pechmann dye and dithienyl-diketopyrrolopyrrole as co-electron acceptors: tuning HOMO/LUMO energies and photovoltaic performances

Three conjugated D–A terpolymers PBPD1, PBPD2, and PBPD3 with the Pechmann dye-derived electron acceptor and dithienyl-diketopyrrolopyrrole as co-acceptors are presented. Their HOMO/LUMO energies and absorptions can be tuned by varying the ratios of two acceptors. Importantly, HOMO energies of these terpolymers are lowered by increasing the content of the Pechmann dye-derived electron acceptor in the conjugated backbones. The thin blend films of PBPD1, PBPD2, and PBPD3 with PC71BM have been tested as active layers for polymer solar cells. The blend of PBPD1:PC71BM shows a high power conversion efficiency of up to 5.21%, which is higher than that with the blend of the dithienyl-diketopyrrolopyrrole-based polymer without the Pechmann dye-derived electron acceptor and PC71BM. In addition, the neat thin films of PBPD1, PBPD2, and PBPD3 exhibit ambipolar semiconducting properties with hole and electron mobilities up to 0.604 cm2 V−1 s−1 and 0.225 cm2 V−1 s−1.

Thiepin‐Fused Heteroacenes: Simple Synthesis, Unusual Structure, and Semiconductors with Less Anisotropic Behavior

The simple one-pot syntheses of sulfur-rich thiepin-fused heteroacences with an alkylidene-fluorene framework, THA1 and THA6 (thiepin-fused heteroacene 1 or 6, in which the thiepin is conjugated at both ortho positions with SCH3 or SC6 H13 , respectively), is reported. Based on electrochemical studies and theoretical calculations, their LUMO energies are relatively low (-3.26 eV), and their HOMO and HOMO-1 orbitals are nearly degenerate. The thiepin ring contributes mainly to HOMO-1 and LUMO orbitals, however, HOMO orbitals dominantly reside on thienoacence rings. Within the crystal of THA1, the molecules adopt a herringbone arrangement and multiple intermolecular interactions lead to the formation of a 2D network. Interestingly, THA6 shows totally different intermolecular arrangements. Organic field-effect transistor (OFET) devices show both compounds exhibiting p-type semiconducting behavior. Thin films or microcrystals of THA1 possess relatively high hole mobility. Moreover, the mobilities of the microcrystal of THA1 along three directions are in the same order, thus the hole-carrier transporting within the hexagonal-plane of microcrystal of THA1 exhibits less anisotropic behavior. In comparison, both thin films and microrods of THA6 show low hole mobilities. This agrees well with the intermolecular arrangements and interactions within crystal of THA6. Further theoretical calculations reveal that significant intermolecular electronic coupling among HOMO-1 orbitals and sulfur atoms play an important role in intermolecular electronic coupling for THA1.

The adjustment of bandgap and coplanarity of diketopyrrolopyrrole-based copolymers through fine-tuning of the conjugated backbones and applications in thin film field effect transistors

In order to demonstrate the influence of structural fine-tuning on bandgap and semiconductor performance of π-conjugated polymer materials, three new diketopyrrolopyrrole (DPP) based copolymers P1, P2 and P3 with monomers, i.e., 2-phenylpyridine, 2-(thiophen-2-yl)pyridine and 2-(thiophen-2-yl)thiazole, respectively, have been synthesized using a typical Suzuki cross-coupling polycondensation. The DFT calculations demonstrate that polymer P3 displays high backbone coplanarity in comparison to polymers P1 and P2. Absorption spectra results reveal that P3 exhibits a remarkable red-shifted absorption profile, narrow band gap and broad absorption. The thin film FET measurements show that P3 possesses the highest hole mobility (μh) up to 1.25 cm2 V−1 s−1 and on/off (Ion/off) ratio as high as 108. Those results demonstrate that the fine-tuning of the π-conjugated backbone can significantly affect the band gaps and coplanarities, and ultimately improve the semiconducting performances.

Conjugated terpolymers synthesized by incorporating anthracene units into the backbones of the diketopyrrolopyrrole-based polymers as electron donors for photovoltaic cells

Three new conjugated D–A terpolymers PADPP1, PADPP2 and PADPP3, which contain diketopyrrolopyrrole (DPP) as electron acceptors and thiophene/anthracene as electron donors, are described. In comparison with PDPP3T which contains just DPP and thiophene units, the DPP moieties are partially replaced with anthracene units in PADPP1, PADPP2 and PADPP3. The HOMO/LUMO levels of PADPP1, PADPP2 and PADPP3 are slightly enhanced in comparison with those of PDPP3T. Moreover, the incorporation of the anthracene units into the backbones leads to the formation of nanofibrils with an appropriate width within the blending thin films of PADPP2 with PC71BM. The short circuit currents (JSC) of the photovoltaic cells with blends of PADPP1, PADPP2 and PADPP3 with PC71BM are higher than those with the PDPP3T/PC71BM blend. As a result, PADPP1, PADPP2 and PADPP3 display better photovoltaic performances than PDPP3T after blending each polymer with PC71BM under the same conditions. The PCE of the photovoltaic cell of the PADPP2/PC71BM blending thin film at a weight ratio of 1 : 2 as the active layer can reach 6.24%.