Influence of different anchoring groups in indoline dyes for dye-sensitized solar cells: Electron injection, impedance and charge recombination

For developing panchromatic dyes, we focus on the effect of rhodanine acceptor on photovoltaic performances in D-pi-A indoline dye. Upon changing from cyanoacetic acid (dye C-CA) to rhodanine-3-acetic acid (dye C-RA) as acceptor and anchoring group, C-RA shows broader absorption band, which can overlap with the solar spectrum more preferably. However, the power conversion efficiency of DSSCs based on C-RA (0.57-0.90%) is one order of magnitude with respect to C-CA (8.49%). The distinct difference of IPCE values between C-CA and C-RA is predominately attributed to the different excited electron injection yield (Phi(inj)). The relatively short excited electron lifetime and the isolation of LUMO orbital from anchoring group in C-RA result in the low photo-excited electron injection efficiency with low J(SC). Moreover, with respect to C-CA, the systematic SLIT and EIS studies demonstrate that C-RA possesses the relatively low injection charge density in the TiO2 electrode and fast charge recombination rate, leading to a low V-OC. Our studies are highly helpful to the design of novel metal-free D-pi-A organic sensitizers, especially for those using rhodanine-3-acetic acid as acceptor. (c) 2013 Elsevier B.V. All rights reserved.