Enhanced performance of quasi-solid-state dye-sensitized solar cells by tuning the building blocks in D-(π)-A′-π-A featured organic dyes

A series of D-(pi)-A'-pi-A featured organic dyes with different numbers of 3,4-ethylenedioxythiophene (EDOT) bridges and different anchoring groups, i.e., cyanoacrylic acid or rhodanine-3-acetic acid, have been designed and synthesized for application in quasi-solid-state dye-sensitized solar cells (DSSCs). The absorption, electrochemical and photovoltaic properties are systematically investigated. Upon the incorporation of an auxiliary EDOT unit into sensitizers FNE60 and FNE61 with D-A'-pi-A configuration, sensitizers FNE62 and FNE63 with D-pi-A'-pi-A configuration exhibit much broader absorption spectra, which is beneficial to the light-harvesting capability and photocurrent generation. When the cyanoacrylic acid group in sensitizers FNE60 and FNE62 is replaced by a much stronger electron-withdrawing group, rhodanine-3-acetic acid, strengthened intramolecular charge transfer interactions are realized, which results in the significantly bathochromically shifted maximum absorption wavelengths for sensitizers FNE61 and FNE63. However, the methylene group in the rhodanine-3-acetic acid unit interrupts the LUMO delocalization on the anchoring group in sensitizers FNE61 and FNE63, as revealed by theoretical calculation, which may result in less effective electron injection from the LUMO to the conduction band of the titania semiconductor. Consequently, the quasi-solid-state DSSC based on FNE62 exhibits a highest power conversion efficiency of 8.2%, which illustrates good long-term stability after continuous light soaking for 1000 h.