Efficient Far Red Sensitization of Nanocrystalline TiO2 Films by an Unsymmetrical Squaraine Dye

An asymmetric squaraine sensitizer comprising an anchoring group was engineered at the molecular level and synthesized. The functionalized novel squaraine sensitizers upon anchoring onto a TiO2 film exhibit an unprecedented incident photon to current conversion efficiency of 85%. The photovoltaic data of this sensitizer using an electrolyte having composition of 0.6 M M-methyl-N-butyl imidazolium iodide, 0.05 M iodine, 0.1 M LiI, 0.05 M tert-butylpyridine in a 15/85 (v/v) mixture of valeronitrile and acetonitrile revealed a short circuit photocurrent density of 10.5 ± 0.2 mA/cm2, an open circuit voltage of 603 ± 10 mV, and a fill factor of 0.71 ± 0.02, corresponding to an overall conversion efficiency of 4.50% under standard AM 1.5 sunlight.