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Donor-Acceptor Polymers for Organic Photovoltaics
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Desta Gedefaw, Mats R. Andersson
The indacenodithiophene (IDT) unit has an extended fused-ring and rigid coplanar structures, which are beneficial for p-electron delocalization and preventing rotational disorder, which reduces reorganization energy and enhances charge carrier mobility.111 Besides a well-developed synthetic methodology for the synthesis of the core unit (Scheme 8.10), the IDT unit has reaction sites for easy modifications. For instance, alkyl side chains can be easily attached to the bridging atom for enhancing solubility and tuning the properties of the final materials. Another key advantage of the IDT unit is the possibility of introducing atoms like silicon, nitrogen, and germanium and the possibility of functionalization to make it ready for coupling reactions. In order to extend the conjugating further, groups like thienothiophene can be used instead of thiophene.
Morphology Evolution and Interfacial Design of Conjugated Polymer-Based Photovoltaics
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Li et al. found that the diameter of the DPP polymer fibrils is governed by polymer solubility and that the fibril width is crucial for determining the phase separation of the BHJ films.70,71 Specifically, the conjugated polymer backbone and the side chains attached to the DPP units significantly influence the solubility of the polymer and, hence, the fibril width. For example, integration of larger size π-conjugated segments can decrease the fibril size to a range that affords a suitable phase separation in the BHJ films (Figure 14.5A). Polymers with shorter side chains on the DPP unit formed smaller width fibrils, allowing more excitons to reach the donor–acceptor interface for charge generation. Moreover, introducing alternating short and long alkyls in DPP-based terpolymers can optimize domain spacing and phase purity in the resultant BHJ films, which further improves solar cell efficiency72. The branching point of the alkyl chains on the DPP unit also plays an important role on the morphology of the BHJ and device performance. McCulloch and coworkers investigated thienothiophene-substituted DPP polymers with thiophene as a copolymerization unit.73 When moving the alkyl-chain branching position away from the polymer backbone (C1, C2, C3 in Figure 14.5B), the π−π stacking distance of the polymer chains could be varied which impacted the polymer crystallinity and photovoltaic properties. From C1 to C2 and C3, GIXD characterizations showed a small decrease in the π−π stacking distance (3.59 to 3.52 Å) and an increase in the degree of crystallinity.
Flexible and Organic Solar Cells
Published in Run-Wei Li, Gang Liu, Flexible and Stretchable Electronics, 2019
In order to further improve the efficiency, Eq. (2.3) suggests that both JSC and VOC need to be optimized. One strategy to achieve this goal is to design a polymer that has a deep-lying HOMO while keeping a narrow bandgap. A new generation of copolymers is then introduced, in which alternating electron-rich (i.e., donor) and electron-deficient (i.e., acceptor) moieties are incorporated in the polymer backbone [26, 41, 42]. This donor-acceptor (D-A) approach (in some cases named as push–pull) enables the construction of a low-bandgap polymer with tunable energy levels. Typically, the electron-rich fragment has high-lying HOMO levels and the acceptor has low-lying LUMO level. The repeating D-A units determine the bandgap and energy levels of the polymer. A simplified molecular orbital theory is depicted in Fig. 2.7 [27]. Hence, the HOMO and LUMO of the polymer can be tuned individually by selecting the desired donor and acceptor units [42, 43]. This D-A approach has made great success in designing low-bandgap polymers and dominates the development of new OSC materials in the community. A variety of D-A polymers are developed based on this concept. The most well-known donor units include fluorene, cyclopentadithiophene (CPDT), oligothiophene, benzodithiophene (BDT), indacenodithiophene (IDT), etc. The most well-known acceptor units include benzothiadiazole (BT), thieno[3,4-b] thiophene (TTP), 4,7-di[2-thienyl]-2,1,3-benzothiadiazole (DTBT), dithienyl-diketopyrrolopyrrole (DTDPP), thienothiophene (TT), thienopyrroledione (TPD), isoindigo (IID) moieties, etc. The chemical structures of these moieties are summarized in Fig. 2.8.
Molecular engineering of the efficiency of new thieno[3,2-b]thiophene-based metal-free dyes owning different donor and π-linkers groups for use in the dye-sensitised solar cells: a quantum chemical study
Published in Molecular Physics, 2021
Hossein Roohi, Nafiseh Motamedifar
The cyanoacrylic acid group consists of strong electron-withdrawing moieties of the cyano and carboxyl groups. Due to the extensively conjugated π-bridge, these dyes exhibit high extinction coefficients. The nature of the π-conjugated bridge in the dye influences not only the region of light absorbed by the DSSCs but also the degree of electron injection from the dye’s excited state to the semiconductor. By strategically addition of thienothiophene (L1), 2,2′-bithieno[3,2-b]thiophene (L2) and 2,3-dihydrothieno[3,4-b][1,4]dioxine (L3) and benzo[c]thiophene (L4) linkers between three different donor groups and one acceptor group, the electronic structures and in turn, photo-physical characteristics of the designed dyes have been explored by DFT and TD-DFT calculations.
New small organic molecules based on thieno[2,3-b]indole for efficient bulk heterojunction organic solar cells: a computational study
Published in Molecular Physics, 2020
Mohamed Hachi, Ahmed Slimi, Asmae Fitri, Souad ElKhattabi, Adil Touimi Benjelloun, Mohammed Benzakour, Mohammed Mcharfi
In this study, novel D-π-A-π-D conjugated small compounds containing thieno[2,3-b]indole with different π-spacers have been designed for BHJ OSCs based on the experimentally excellent material R. We have investigated theoretically by using DFT/B3LYP/6-31G(d,p) method their structural, electronic, and photovoltaic properties. The absorption has been also evaluated by TD-PBE0/6-311G(d,p) level of the same theory. The results indicate that the substitution of thiophene by the furan, thienothiophene, thiazole and thiazolothiazole improve strongly the properties of the BHJ compounds. The comparison of the different designed compounds shows that the BHJ-4a substituted by thiazolothiazole spacer exhibits more planar structure and seems to be the best candidate for BHJ organic solar cells. Its low band gap, high open-circuit voltage up to 1.534 eV and broad UV-visible absorption make it very favourable for OPVCs. As well, we found that the highest power conversion efficiency could be achieved for BHJ-2a is over 7% by the Scharber model. Finally, the reference compound (R) has been designed and studied as donor molecule blended with PCBM (R:PCBM) to improve the efficiency of the optimised BHJ solar cells. Also, the energy band gap diagram of BHJ OPVCs has been simulated.
Molecular design of supramolecular polymers with chelated units and their application as functional materials
Published in Journal of Coordination Chemistry, 2018
Igor E. Uflyand, Gulzhian I. Dzhardimalieva
Of interest is a number of Fe2+-, Zn2+-, Ni2+-, Cu2+-MSPs, obtained on the basis of 2,6-bis (2-oxazolinyl) pyridine building blocks consisting of pyridine flanked by two oxazoline rings as a tridentate binding site bridged with thiophene, bithiophene, and thienothiophene as a linker [90]. In particular, it turned out that for Fe2+-, Zn2+-, Cu2+-MSPs a large increase in fluorescence was observed with an increase in concentration of metal ions, while Ni2+-MSP exhibited only fluorescent quenching.