In this work, we investigated diketopyrrolopyrrole (DPP) derivatives as potential donor materials for fullerene:DPP solar cells. The derivatives 3,6-bis­(5-(benzofuran-2-yl)­thiophene-2-yl)-2,5-bis­(2-ethylhexyl)­pyrrolo­[3,4-c]­pyrrole-1,4-dione (DPP­(TBFu)2) and 3,6-bis­(5-(benzothiophene-2-yl)­thiophene-2-yl)-2,5-bis­(2-ethylhexyl)­pyrrolo­[3,4-c]­pyrrole-1,4-dione (DPP­(TBTh)2) were modified by introducing a nitrogen atom into the terminal moiety of the molecule. Our quantum-chemical calculations predicted that this modification would increase the rigidity of the molecular structure and increase the ionization potential relative to the original DPP derivatives. The higher ionization potential primarily supports an enhancement in the open circuit voltage, and a more rigid molecular structure will contribute to reduced nonradiative losses. We experimentally verified the fullerene:DPP solar cell concept based on the coincidence of a smaller driving force for charge separation at the donor/acceptor interface and the crystallinity of the studied DPP derivatives for preparing effective photovoltaic devices. The reduction of the driving force for charge separation could be overcome by more structured/packed donor DPP materials; the delocalization of electrons and holes in such structured materials improves charge separation in OPV devices. Using wide range of experimental methods, we determined the parameters of the studied DPP materials with PC70BM in thin films. This work contributes to practical applications by verifying the concept of this organic solar cell design.

A series of novel X-shaped push-pull compounds based on benzene-1,2-dicarbonitrile has been designed, synthesized and further investigated by X-ray analysis, electrochemistry, absorption and emission spectra, SHG experiment and quantum-chemical calculations. The obtained data were compared with those for isolobal 5,6-disubstituted pyrazine-2,3-dicarbonitriles. Structure-property relationships were elucidated. The extension, composition and planarization of the π-linker used as well as the electron-withdrawing ability of both dicyano-substituted acceptor units affect the linear and nonlinear properties of the target charge-transfer chromophores most significantly.

An optimized fabrication of bulk-heterojunction solar cells (BHJ SCs) based on previously reported diketopyrrolopyrrole donor, ethyl-hexylated DPP(TBFu)2, as well as two new DPP(TBFu)2derivatives with ethyl-hexyl acetate and diethyl acetal solubilizing side-chains and PC60BM as an acceptor is demonstrated. Slow gradual annealing of the solar cell causing the effective donor-acceptor reorganization, and as a result higher power conversion efficiency (PCE), is described. By replacing a hole transporting layer PEDOT:PSS with MoO3we obtained higher PCE values as well as higher thermal stability of the anode contact interface. DPP(TBFu)2derivative containing ethyl-hexyl acetate solubilizing side-chains possessed the best as-cast self-assembly and high crystallinity. However, the presence of ethyl-hexyl acetate and diethyl acetal electrophilic side-chains stabilizes HOMO energy of isolated DPP(TBFu)2donors with respect to the ethyl-hexylated one, according to cyclic voltammetry.

Three bis[octakis-(2-thienyl)phthalocyaninato] rare-earth metal(III) phthalocyanine complexes (Pc[Formula: see text]Pr, Pc[Formula: see text]Sm, Pc[Formula: see text]Gd) were synthesized for the first time. The new compounds were characterized by UV-vis, NMR, FT-IR, mass spectroscopies as well as elemental analysis and electrochemistry. Production of singlet oxygen was also estimated by 9,10-dimethylanthracene method.

Nine new quadrupolar chromophores based on diketopyrrolopyrrole were designed and prepared by cross-coupling reactions. The property tuning has been achieved by structural variation of the peripheral substituents (donor) and enlargement of the π-system. Fundamental properties of target molecules were studied by differential scanning calorimetry, electrochemistry, and absorption and emission spectra. Nonlinear optical properties were studied by measuring the third harmonic generation. The experimental data were completed by quantum-chemical calculations and structure–property relationships were elucidated.