Impact of backbone linkage positions on the molecular aggregation behavior of polymer photovoltaic materials

It is imperative to advance the structural design of conjugated materials to achieve a practical impact on the performance of photovoltaic devices. However, the effect of the linkage positions (meta-, para-) of the backbone on the molecular packing has been relatively little explored. In this study, we have synthesized two wide-bandgap polymer photovoltaic materials from identical monomers with different linkage positions, using dibenzo[c,h][2,6]-naphthyridine-5,11-(6H,12H)-dione (DBND) as the building block. This study shows that the para-connected polymer exhibits an unexpected 0.2 eV higher ionization potential and a resultant higher open-circuit voltage than the meta-connected counterpart. We found that different linkage positions result in different intermolecular binding energies and molecular aggregation conformations, leading to different HOMO energy levels and photovoltaic performances. Specifically, theoretical calculations and 2D-NMR indicate that P(p-DBND-f-2T) performs a segregated stacking of f-2T and DBND units, while P(m-DBND-f-2T) films form π-overlaps between f-2T and DBND. These results show that linkage position adjustment on the polymeric backbone exerts a profound influence on the molecular aggregation of the materials. Also, the effect of isomerism on the polymer backbone is crucial in designing polymer structures for photovoltaic applications.

Copolymers of carbazole and phenazine derivatives: minor structural modification, but totally different photodetector performance

Through the subtle modification of the molecular structure, four donor–acceptor type conjugated polymers were designed, and demonstrated very different device performances with the highest photodetectivity achieved up to 6.2 × 10¹² Jones.

Enhancing the photovoltaic properties of low bandgap terpolymers based on benzodithiophene and phenanthrophenazine by introducing different second acceptor units

Two D–A type random terpolymers PBDTT-PPzIID and PBDTT-PPzDPP were synthesized by copolymerizing a donor and two acceptor units. The PBDTT-PPzDPP-based device shown a PCE of 5.91%.

Improving Photovoltaic Performance of the Linear A-Ar-A-type Small Molecules with Diketopyrropyrrole Arms by Tuning the Linkage Position of the Anthracene Core

Two isomeric A-Ar-A-type small molecules of DPP2An(9,10) and DPP2An(2,6), were synthesized with two acceptor arms of diketopyrropyrroles (DPP) and a planar aryl hydrocarbon core of the different substituted anthracene (An), respectively. Their thermal stability, crystallinity, optoelectronic, and photovoltaic performances were investigated. Significantly red-shifted absorption profile and higher HOMO level were observed for the DPP2An(2,6) with 2,6-substituted anthracene relative to the DPP2An(9,10) with 9,10-substituted anthracene, as the former exhibited better planarity and a larger conjugate system. As a result, the solution-processing solar cells based on DPP2An(2,6) and PC71BM (w/w,1:1) displayed remarkably increased power conversion efficiency of 5.44% and short-circuit current density (Jsc) of 11.90 mA/cm(2) under 1% 1,8-diiodooctane additive. The PCE and Jsc values were 3.7 and 2.9 times those of the optimized DPP2An(9,10)-based cells, respectively. This work demonstrates that changing the linkage position of the anthracene core in the A-Ar-A-type SMs can strongly improve the photovoltaic properties in organic solar cells.

Enhancing the performance of polymer solar cells using CuPc nanocrystals as additives

There is an increasing interest in the use of different nanoparticles as additives in polymer solar cells for enhancing the light absorption of active layers as well as their power conversion efficiency (PCE). In this paper, we report a PCE enhancement by simply adding copper phthalocyanine (CuPc) nanocrystals into photovoltaic devices based on a poly(3-hexylthiophene) (P3HT): fullerene system. Two kinds of device structure were studied: the first one is a CuPc nanocrystal suspension spin coated on the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate-coated substrate; the second one is the CuPc nanocrystal suspension added into the active layer solutions. It is proved that incorporating organic semiconductor nanocrystals into the active layer can help trap light and enhance the crystallinity of the active layers, thus improving the device performance. This strategy might be generally compatible with a broad range of organic photovoltaic materials and offers an effective approach to enhance the device performance.

Improved photovoltaic performance of a 2D-conjugated benzodithiophene-based polymer by the side chain engineering of quinoxaline

To investigate the influence of side chains of quinoxaline on the photovoltaic performances, a novel D–A-type polymer of PBDTDT(Qx-3)-T was synthesized and characterized, in which BDT-T, T and Qx-3 were used as the donor (D) unit, π-bridge and acceptor (A) unit, respectively.

The side chain effect on difluoro-substituted dibenzo[a,c]phenazine based conjugated polymers as donor materials for high efficiency polymer solar cells

Conjugated polymers with difluoro-substituted dibenzo[a,c]phenazine as the acceptor unit and benzodithiophene derivatives as the donor unit were prepared and used for polymer solar cells.

Two-dimensional quinoxaline based low bandgap conjugated polymers for bulk-heterojunction solar cells

Photovoltaic cells based on the two-dimensional quinoxaline-based polymers,P2andP3, exhibited PCEs of over 3% compared to the PCE of less than 2% in theP1-based device.

A concise method to prepare novel fused heteroaromatic diones through double Friedel–Crafts acylation

Different types of fused heteroaromatic diones have been successfully prepared through the concise intramolecular double Friedel–Crafts acylation strategy.