Oligothiophene-Containing Coumarin Dyes for Efficient Dye-Sensitized Solar Cells

Abstract

We have developed oligothiophene-containing coumarin dyes fully functionalized for dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs). DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400−800 nm. A solar energy-to-electricity conversion efficiency (η) of 7.4% was obtained with a DSSC based on 2-cyano-3-[5‘-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2‘]bithiophenyl-5-yl]acrylic acid (NKX-2677) under simulated AM 1.5G irradiation (100 mW cm^-2) with a mask: short-circuit current density (J_sc) = 13.5 mA cm^-2; open-circuit voltage (V_oc) = 0.71 V; fill factor (FF) = 0.77. Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO₂ is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity.