Ferrocenylethenyl-substituted oxadiazoles with phenolic and nitro anchors as sensitizers in dye sensitized solar cells

Abstract

Three new ferrocenyl oxadiazoles, viz. (E)-2-(4-hydroxyphenyl)-5-(2-ferrocenyl-ethen-1-yl)-1,3,4-oxadiazole (D2), (E)-2-(4-nitrophenyl)-5-(2-ferrocenyl-ethen-1-yl)-1,3,4-oxadiazole (D3) and (E)-3-(4-nitrophenyl)-5-[5-(2-ferroceneylethen-1-yl)-1,3,4-oxadiazol-2-yl]-1,2,4-oxadiazole (D4) derived from (E)-3-ferrocenylacrylic acid (D1) having phenolic or nitro anchors, have been synthesized and characterized using microanalyses and relevant spectroscopic techniques. UV-Vis spectroscopic studies indicate that with respect to ferrocene, the electronic absorption bands of the new compounds are bathochromically shifted up to 600 nm with a concomitant enhancement in their intensities. All four compounds have been used as photosensitizers in TiO₂-based dye-sensitized solar cells (DSSCs). The photovoltaic performances and charge transport properties (EIS spectra) of these compounds were studied to appraise their dye performance. All four compounds displayed good photovoltaic performances. However, compounds D2 and D4 displayed superior performance, which might be due to the better electronic communication between the ferrocenyl moiety and the six membered aromatic ring with their –OH/NO₂ anchors having five membered oxadiazole spacers, as well as the high dye loading of these compounds on the TiO₂ surface, which suppresses charge recombination, prolongs electron lifetime, and decreases the total resistance of DSSCs. The assembly fabricated using D4 performed better with an overall conversion efficiency η of 4.70%, J_sc of 10.33 mA cm⁻² and V_oc of −0.712 V.