Solution processable polymer-based organic photovoltaics offer tremendous opportunities for applications requiring flexible, translucent or aesthetically pleasing designs, with potential for low-cost roll-to-roll mass production. However, progress in moving the organic photovoltaic technology from lab-scale to commercial applications has been slow, generating skepticism around the commercial viability of the technology. Organic photovoltaic research is often carried out on small-area research cells fabricated under inert conditions using techniques such as spin coating that do not translate to mass production. While high research cell performance can be achieved, the materials selected or conditions used for fabrication are typically not amenable to scale-up. This paper will focus on solving some of the technical challenges associated with scaling polymer-based bulk heterojunction organic photovoltaics to high-performance large-area modules. Efforts to develop materials that are stable to fabrication in air, have good solubility, and enable deposition of thick (>300 nm) photoactive layers are described, leading to organic photovoltaic modules reaching 8% power conversion efficiency (PCE).

Opportunities for fine-tuning conjugated polymer properties are needed to continue enhancing photovoltaic performance. Herein an amide-or ester-functionalized 3-fluorothieno[3,4-b]thiophene (FTT(N) or FT(E)) were used in alternating copolymers with benzo(1,2-b:4,5-b')dithiophene (BDT). The amide-functionalized polymer had a blue-shifted absorption spectrum and was blended with the ester-functionalized polymer in photovoltaic devices in an effort to increase light absorption of the photoactive layer. A 50:50 blend of the two polymers resulted in unfavorable morphology, leading to decreased power conversion efficiency (PCE), however, the blended mixture had a slightly enhanced stability relative to devices containing a single PBDT-FTT(E) polymer. Reducing the loading of the amide-functionalized polymer, PBDT-FTT(N), to 3 wt.% led to a certified PCE of 10.1%. To allow a higher loading of the FTT(N) monomer in the photoactive layer, a random copolymer containing both FTT(N) and FTT(E) was also prepared, which exhibited broader absorption and reached a PCE of 7.9%.

A synthetic approach is established to provide a monofunctional telechelic poly(3-octylthiophene) (P3OT) bearing a single bromine-substituted end group that is of potential use in the preparation of well-defined block copolymers. Telechelic P3OT was prepared via a chain growth process by a catalyst-transfer condensation polymerization (CTCP) of 5-bromo-4-octyl-2-thienylmagnesium iodide initiated by a phenylnickel(H) initiator. Optimization of the conditions for quenching the reaction allowed for the installation an a-bromo functionality at the terminus of the polymer. We demonstrate the utility of this well-defined monofunctional polymer, Ph-P3OT-Br, by coupling it to a poly(quinoxaline) (PQ) bearing boronate ester end groups to provided a new class of donor-acceptor-donor (D-A-D) triblock copolymers. The formation of the triblock copolymers was confirmed by gel-permeation chromatography (GPC) and (1)H NMR spectroscopy. The optical properties of the polymers were investigated using UV-visible absorption and fluorescence spectroscopy. Efficient quenching of the fluorescence from the individual blocks of the triblock copolymers is consistent with the occurrence of electron transfer. AFM images illustrate a nanoscale phase separation of the electron-rich P3OT and electron-poor PQ blocks.

A majority of conjugated organic polymers are election-rich materials, with far fewer electron-poor (i.e., electron accepting) analogues. Here we report the synthesis and preliminary characterization of new class of electron-poor poly(arylene ethynylene)s (PAEs) that contain 5,8-quinoxaline ethynylene repeat units. While various PAE copolymers consisting of alternating electron-rich and electron-poor units display lower bandgaps than poly(phenylene ethynylene)s, the poly(5,8-quinoxaline ethynylene) (PQE) reported in this study has a higher electron affinity and lower bandgap (2.25 eV) than many of these donor-acceptor materials. In comparison to poly(5,8-quinoxaline)s (PQs), which do not have an ethynylene linkage between the quinoxalines, the PQE has a red-shifted absorption spectrum that is consistent with a more highly conjugated and planar backbone. In addition, the PQE has a lower electrochemical reduction potential than both a corresponding PQ and a donor acceptor alternating PAE copolymer that contains the quinoxaline unit as the electron-poor component.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The authors report the synthesis of three different copolymers incorporating benzodisdioxole units. By constraining the alkoxy units, the authors show a large Stokes shift in the resulting donor-acceptor copolymers.

New poly(1,4-phenylene ethynylenes)s (PPEs), in which each phenylene unit is substituted with both semifluoroalkoxy(-O(CH2)m(CF2)nF) and dodecyloxy (-O(CH2)(12)H) groups, are amphiphilic by virtue of the self-aggregating properties fo the dissimilar side chains. Sonogashira polymerization of 4-iodophenylacctylenes bearing semifluoroalkox y and alkoxy groups in the 2- and 5-positions, respectively, alfords polymers with regular relative placement of the dissimilar side chains (i.e., "regioregular" materials containing only "head-to-tail" drads) This provides a Janus type structure The assembly of these polymers was studied as a function of the length of the fluoroalkyl segment in the side chain by X-ray diffraction, differential scanning calorimetry, and UV-vis spectroscopy. The properties of these polymers were compared to analogues with random relative placement of side chains (i.e., materials containing a mixture of "head-to-head", "tail-to-tail" and "head-to-tail" drads), and to a nonfluorinated analogue. In contrast to the highly ordered and oriented solid phases formed by alkyl/semifluoroalkyl substituted poly(bithiophene)s, and despite their defined molecular structure, the amphiphilicity of the new semifluoro PPEs impedes their crystallization. While the overall structure of the regioregular polymer is amphiphilic, in which the dissimilar side chains are expected to segregate, we ascribe the lack of crystallinity to the disruption of side chain crystallization by virtue of having the alkyl and fluoroalkyl segments withing a single side chain. These side chain cannont pack in an interdigitated fashion by virtue of the disparate segments, thereby leading to poorly ordered, or amorphous, solid materials.

Phenyleneethynylene-based conjugated copolymers using benzo[1,2-d:4,5-d']bis[1,3]dioxole (BDO) in the repeating unit are reported. The electronic structure of the BDO unit imparts a localized HOMO topology while the LUMO is delocalized over the polymer backbone, so that the lowest optical absorption band of the polymer has considerable intramolecular charge transfer character. This contrasts with published donor-acceptor polymers with localized LUMO and delocalized HOMO. The very large Stokes shifts of the monomers, which are due to the small oscillator strength of the lowest optical transition, are largely retained in the polymers as a result of covalently constrained dihedral angles in the substituents (not the backbone), as predicted/explained by calculations.

Poly(2,5-disubstituted-1,4-phenylene ethynylene)s, PPEs. are generally synthesized by Pd-catalyzed Coupling polymerizations of appropriately substituted 1.4-diiodobenzenes and 1.4-diethynylbenzenes (i.e., condensation polymerization of A-A and B-B type monomers). If the monomers are not symmetrically substituted. this results in an irregular substitution pattern of the side chains along the polymer backbone. As with other classes of conjugated polymers, the relative placement of side chain along the backbone should influence the properties of the materials. We report a new synthetic approach to prepare regioregular unsymmetrically substituted PPEs by polymerization of 4-iodophenylacetylenes (i.e., a condensation polymerization of a single A-B type monomer). We have synthesized both the regiorandom and regioregular PPEs from unsymmetrically Substituted monomers. We provide a detailed discussion of various approaches to the synthesis of PPEs with different regioregularities and provide a preliminary description of the differences between regioregular and regiorandom analogues.