Ceylan Zafer

A new 1H-pyridin-(2E)-ylidene ruthenium complex as sensitizer for a dye-sensitized solar cell

The new heteroleptic ruthenium(II) complex containing a 1H-pyridin-(2E)-ylidene (PYE) ligand was synthesized and characterized using UV/Vis, FTIR, and NMR spectroscopies, mass spectrometry, elemental analysis, and cyclic voltammetry. The photovoltaic performance of the ruthenium complex as a charge transfer photosensitizer in nc-titanium dioxide based dye-sensitized solar cell was studied and compared with cis-bis(isothiocyanato)(2,2′-bipyridyl-4,4′-dicarboxylato)(2,2′-bipyridyl-4,4′-di-nonyl)ruthenium(II) (Z907) under standard AM 1.5 sunlight. The complex CS90 gave a photocurrent density of 1.80 mA cm−2, 400 mV open-circuit potential, and 0.58 fill factor yielding an efficiency of 0.42% where the reference Z907 yielded an efficiency of 4.12%. The decrease in conversion efficiency observed for CS90 is attributed to a steric interaction between PYE and the TiO2 surface that prevents optimum binding and also restricts ligand dynamics that are associated with oxidation state changes.

Impact of the different electron-releasing subunits on the dye-sensitized solar cell performance of new triphenylamine-benzimidazole based molecules.

New triphenylamine-benzimidazole type small molecules with different electron-releasing groups were designed and synthesized to investigate their photovoltaic performances in dye sensitized solar cells (DSSCs). Their good visible absorptions covering the 400-535 nm in addition to suitable lowest unoccupied molecular orbital (LUMO) energy levels between -3.03 and -3.11 eV make good candidates them for DSSC devices. Fluorescence quenching studies of the dyes with pristine titania support the good electron injection to conduction band of TiO2. Time resolved measurements of the dyes in solutions indicate the occurence of charge generation during the excited state. One of the used dyes in DSSC devices, TPA5a, carrying a methoxy group in triphenylamine part of the structure, gave much higher power conversion efficiency (PCE) value of 4.31% as compared to the other derivatives. Device fabricated from TPA5a dye gives good external quantum efficiency (EQE) value above 70% at 460 nm. Also, electron impedance spectroscopy (EIS) analysis of the devices gives a good explanation of the understanding of the cell performances.

Optoelectronic performance comparison of new thiophene linked benzimidazole conjugates with diverse substitution patterns

In an approach to develop efficient organic optoelectronic devices to be used in light-driven systems, a series of three thiophene linked benzimidazole conjugates were synthesized and characterized. The combination of two thiophene rings to a benzimidazole core decorated with different functional groups (such as OCH3, N(CH3)2, CF3) resulted in donor-acceptor type molecular scaffold. The effect of the electronic behavior of the substituents on the optical, electrochemical, morphological and electron/hole transporting properties of the dyes were systematically investigated. DTBI2 dye exhibited distinct absorption properties among the other studied dyes because N,N-dimethylamino group initiated intramolecular charge transfer (ICT) process in the studied solvents. In solid state, the dyes exhibit peaks extending up to 600nm. Depending on the solvent polarities, dyes show significant wavelength changes on their fluorescence emission spectra in the excited states. Morphological parameters of the thin films spin-coated from CHCl3 solution were investigated by using AFM instrument; furthermore photovoltaic responses are reported, even though photovoltaic performances of the fabricated solar cells with different configurations are quite low.

Synthesis and photophysical characterization of isoindigo building blocks as molecular acceptors for organic photovoltaics

Five isoindigo-based donor-acceptor-donor (D-A-D) type small molecules have been synthesized in order to investigate their intramolecular charge transfer characteristics. UV-vis absorption of these dyes exhibits a wide absorption band ranging from 300 to 650 nm with two distinct bands, giving the narrow bandgaps between 1.72 and 1.85 eV. Taking into account their HOMO-LUMO energy levels and bandgaps, isoindigo dyes have been used in the active layer of organic solar cell (OSC) devices. When these small molecule semiconductors were used as acceptors with the donor poly(3-hexylthiophene-2,5-diyl (P3HT) polymer in the inverted OSC devices, the highest power conversion efficiency (PCE) was obtained as 0.10% for pyrene-substituted isoindigo derivative.