para‐Dialkylaminophenyl Dyes for Efficient Nanocrystalline TiO2 Sensitization in Far‐red Region

Four para‐dialkylaminophenyl (PDAAP1–PDAAP4) bearing carboxyl groups were studied for application to the dye‐sensitized solar cells (DSC). It was found the short spacer CH2 between carboxyl and dialkylaminophenyl chromophore in PDAAP3 and PDAAP4 led to highly efficient monochromatic incident photon‐to‐current conversion efficiencies (IPCE), however the long alkyl group C4H9 attached on aniline moieties in PDAAP2 and PDAAP4 favored improvement of open‐circuit photovoltage. Thus, the solar cell sensitized by PDAAP4, having both short carboxyl groups CH2COOH and long alkyl groups C4H9, exhibited the IPCE maximum of 73% at 670 nm and overall energy conversion efficiency η of 3.06%, representing the highest IPCE and η values so far in dialkylaminophenyl‐based organic dye‐sensitized semiconductor solar cells. Taking advantage of the highly efficient sensitizing ability of PDAAP4 in far‐red region, the data of IPCE above 630 nm of the solar cells were improved greatly by cosensitization with both N3 and PDAAP4. The influences of the TiO2 film thickness and the concentration of 4‐tert‐butylpyridine (TBP) in electrolyte were also investigated.