Alexander N. Solodukhin

Branched triphenylamine-based oligomers for organic electronics

This review involves discussion and analysis of the main advantages and trends of the molecular design of branched triphenylamine-based oligomers and their application in modern organic electronics devices, such as organic solar cells, light-emitting diodes, thin-film field-effect transistors, and sensors.

Star-shaped D–π–A oligothiophenes with a tris(2-methoxyphenyl)amine core and alkyldicyanovinyl groups: synthesis and physical and photovoltaic properties

Synthesis of a series of star-shaped oligomers having a novel electron donating tris(2-methoxyphenyl)amine (m-TPA) core, which is linked through a bithiophene or terthiophene π-bridge with electron-deficient alkyldicyanovinyl (alkyl-DCV) groups, is described. A comprehensive study of the oligomers revealed significant dependence of their physical properties, including absorption, molecular frontier energy levels, crystal packing, and melting and glass transition temperatures, upon the chemical structure. A comparison of their photophysical properties to the nearest analog having the common dicyanovinyl (DCV) groups demonstrated a number of benefits to use alkyl-DCV units for the design of donor–acceptor small molecules: higher solubility, increased electrochemical stability, better photovoltaic performance, and possibility to control the relative physical and photovoltaic properties by a simple adjustment of alkyl and π-bridge lengths. Modification of the well-known triphenylamine (TPA) core in the star-shaped oligomers by methoxy groups increases not only solubility, but also crystallinity of the oligomers, whereas their photovoltaic performance stays on a similar level as their analogs with a TPA core. The study demonstrates that these design strategies represent interesting and simple tools for the effective modulation of properties of star-shaped molecules.

Triphenylamine-Based Push-Pull Molecule for Photovoltaic Applications: From Synthesis to Ultrafast Device Photophysics

Small push–pull molecules attract much attention as prospective donor materials for organic solar cells (OSCs). By chemical engineering, it is possible to combine a number of attractive properties such as broad absorption, efficient charge separation, and vacuum and solution processabilities in a single molecule. Here we report the synthesis and early time photophysics of such a molecule, TPA-2T-DCV-Me, based on the triphenylamine (TPA) donor core and dicyanovinyl (DCV) acceptor end group connected by a thiophene bridge. Using time-resolved photoinduced absorption and photoluminescence, we demonstrate that in blends with [70]PCBM the molecule works both as an electron donor and hole acceptor, thereby allowing for two independent channels of charge generation. The charge-generation process is followed by the recombination of interfacial charge transfer states that takes place on the subnanosecond time scale as revealed by time-resolved photoluminescence and nongeminate recombination as follows from the OSC performance. Our findings demonstrate the potential of TPA-DCV-based molecules as donor materials for both solution-processed and vacuum-deposited OSCs.

Visualization of molecular excitons diffusion

Small organic molecules of the push-pull architecture are rapidly gaining their status in the organic electronics applications. In densely packed molecular films, both intra- and intermolecular interactions play an essential role for the device performance. Here we study two different molecules, a highly symmetric star-shaped one and its newly synthesized single arm analogue, for their photophysical properties. Both chromophores were dissolved in a solid matrix at different concentrations to vary their separation and therefore intermolecular coupling. We show that in both molecules the population relaxation accelerates by more than a factor of 10 at shorter intermolecular distances due to self-quenching thereby reducing the exciton survival time. The transient anisotropy dynamics are also quite similar, with their substantial acceleration at shorter interchromophore distances due to exciton diffusion caused by the Förster-like resonance energy transfer. However, the anisotropy values are noticeably lower for the star-shaped molecule because of intramolecular mixing of different polarization states. Finally, a model is presented that accounts for the observed results.

Design of low band gap small molecules with alkyldicyanovinyl acceptor and different donor groups for efficient bulk heterojunction organic solar cells

A library of low band gap small molecules with alkyldicyanovinyl acceptor and triphenylamine, tris(2- methoxyphenyl)amine or dithienosilole donor groups linked through (oligo)thiophene conjugated spacers was designed and successfully synthesized. Systematic variations of the alkyl chain length and the number of conjugated thiophene rings in the molecules allowed to elucidate the structure-properties relationships for their solubility, absorption spectra, phase behavior, morphology and structure in thin films, as well as photovoltaic properties. Bulk heterojunction organic solar cells prepared from these molecules as donors and PCBM[70] as acceptor by solution processing showed power conversion efficiency up to 5.4 - 6.4%.

The Effect of Star-Shaped Oligothiophenes with a Carbazole Core on Their Structural and Optical Properties

A comparative analysis of the structure and properties of donor–acceptor star-shaped compounds based on oligothiophene with electron-withdrawing dicyanovinyl groups and a different electron-donating branching center—planar 9-phenyl-9H-carbazole and propeller-shaped triphenylamine—has been carried out. It is shown that the absorption maxima in the spectra of 9-phenyl-9H-carbazole derivatives shift to shorter wavelengths, the HOMO energy decreases, and the LUMO energy increases. Moreover, in contrast to propeller-shaped triphenylamine-based compounds, which do not form ordered states, the T-shaped branched molecules based on carbazole form highly ordered crystal structures with different symmetry.

Effect of core modification in star-shaped donor-acceptor oligomers on physical properties and photovoltaic performance

A series of star-shaped donor-acceptor oligomers having alkyldicyanovinyl fragments as electron-withdrawing groups, 2,2′-bithiophene as a conjugated π-bridge and either triphenylamine or its modified analogs (9-phenyl-9H-carbazole derivatives or tris(2-methoxyphenyl)amine as electron-donating cores was designed, synthesized and investigated. Variation of the chemical nature of the donor core allowed elucidating the structure-properties relationships for their solubility, absorption spectra, electrochemistry, phase behavior as well as photovoltaic performance in bulk heterojunction organic solar cells as donor materials in their mixtures with PC70BM. The star-shaped molecules based on triphenylamine and tris(2-methoxyphenyl)amine cores have reduced bandgaps, which leads to more efficient absorption of the sun light and better photovoltaic performance.