Triphenylamine and benzothiadiazole-based D-A-A’ and A’-A-D-D-A-A’ type small molecules for solution-processed organic solar cells

Optoelectronic design and charge transport properties of Benzodifuran (BDF) isomers for organic electronic devices: DFT/TD-DFT insights

The primary goal of this work is to provide a comprehensive analysis of the charge transport and optoelectronic characteristics of all the isomers of benzodifuran (BDF) for organic electronic devices in order to suggest qualified materials/candidates for organic photovoltaic devices. Density functional theory (DFT) calculations were performed for all possible isomers of BDF and results are compared with corresponding experimental known isomers. Time Dependent-Density Functional Theory (TD-DFT) is used for the calculation of the absorption and HOMO-LUMO energy levels. To characterize the electronic charge transport state in these isomers, the ionization potentials (IP), reorganization energies (hole and electron), and electron affinities (EA) of all the isomers are investigated. Comparatively, all the BDF isomers are having low electron and hole reorganization energies and hence they can be used in the organic electronic material fabrication.

Triazine-based Polyelectrolyte as an Efficient Cathode Interfacial Material for Polymer Solar Cells

A novel polyelectrolyte containing triazine (TAZ) and benzodithiophene (BDT) scaffolds with polar phosphine oxide (P═O) and quaternary ammonium ions as pendant groups, respectively, in the polymer backbone (PBTAZPOBr) was synthesized to use it as a cathode interfacial layer (CIL) for polymer solar cell (PSC) application. Owing to the high electron affinity of the TAZ unit and P═O group, PBTAZPOBr could behave as an effective electron transport material. Due to the polar quaternary ammonium and P═O groups, the interfacial dipole moment created by PBTAZPOBr substantially reduced the work function of the metal cathode to afford better energy alignment in the device, thus enabling electron extraction and reducing recombination of excitons at the photoactive layer/cathode interface. Consequently, the PSC devices based on the poly[4,8-bis(2-ethylhexyloxyl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-ethylhexyl-3-fluorothithieno[3,4-b]thiophene-2-carboxylate-4,6-diyl]:[6,6]-phenyl-C₇₁-butyric acid methyl ester (PTB7:PC₇₁BM) system with PBTAZPOBr as CIL displayed simultaneously enhanced open-circuit voltage, short-circuit current density, and fill factor, whereas the power conversion efficiency increased from 5.42% to 8.04% compared to that of the pristine Al device. The outstanding performance of PBTAZPOBr is attributed not only to the polar pendant groups of BDT unit but also to the TAZ unit linked with the P═O group of PBTAZPOBr, demonstrating that functionalized TAZ building blocks are very promising cathode interfacial materials (CIMs). The design strategy proposed in this work will be helpful to develop more efficient CIMs for high performance PSCs in the future.