Synthesis and characterization of novel cyclometalated iridium(III) complexes for nanocrystalline TiO2-based dye-sensitized solar cells

Four novel cyclometalated iridium(III) complexes with the following general formulas were synthesized and characterized using 1H NMR, {1H–1H} COSY, ESI-MS spectral and elemental analysis data: [Ir(C∧N∧C)(ptpy-COOH)]+ (C∧N∧C = 2,6-diphenylpyridinato (1); 2,4,6-triphenylpyridinato (2), ptpy-COOH = 4′-(4-carboxyphenyl)-2,2′:6′,2“-terpyridine) and [Ir(C∧N∧C)(tpy-COOH)]+ (C∧N∧C = 2,6-diphenylpyridinato (3); 2,6-ditolylpyridinato (4), tpy-COOH = 4′-carboxy-2,2′:6′,2″-terpyridine). The photophysical and redox properties and photovoltaic performance of the Ir(III) complexes as photosensitizers in nanocrystalline TiO2-based solar cells were studied and compared to those of cis-diisothiocyanatobis(4,4′-dicarboxy-2,2′-bipyridine)ruthenium(II) (N3). Dye 4 exhibits the highest photovoltaic performance with an overall solar energy conversion efficiency of 2.16%.

► Four novel cyclometalated Ir(III) complexes were synthesized. ► Four novel cyclometalated Ir(III) complexes have longer excited-state lifetimes. ► These Ir(III) complexes may be applicable to the sensitizers for DSSCs.