Influences of the electron donor groups on the properties of thiophene-pyrrole-thiophene and tert-butyl based new ruthenium II bipyridyl sensitizers for DSSCs and DFT studies

RuII(4,5-diazafluoren-9-[4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)]aniline)-(4,4′-dicarboxy-2,2′-bipyridine)(thiocyanate), [Ru(L1)(dcbpy)(NCS)], [K51] and RuII(4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine)-(4,4′-dicarboxy-2,2′-bipyridine)(thiocyanate), [Ru(L2)(dcbpy)(NCS)], [K330] are synthesized as photosensitizers. Photophysical and electrochemical properties are characterized to understand the capabilities of these compounds acting as light sensitizers and injecting electrons to the conduction band of metal-oxide semiconductor. And their photovoltaic properties are investigated in a liquid-state dye sensitized solar cells (DSSCs). A solar energy to electricity conversion efficiencies of 4.92%, 2.52% are obtained under the standard AM 1.5 irradiation (100 mW cm−2) with short-circuit photocurrent densities (Jsc) of 17.48 mA cm−2 and 7.65 mA cm−2, open-circuit photovoltages (Voc) of 506 mV and 490 mV, and fill factors (ff) of 0.66 and 0.56 for K330 and K51, respectively. As a result, K330 sensitized nanocrystalline TiO2 electrode gives higher efficiency than K51 sensitized nanocrystalline TiO2 electrode in dye sensitized solar cell (DSSC). And also density functional theory studies are carried out to estimate the photovoltaic properties of ruthenium complexes in designed states.