Molecular Engineering of Fluorene-Based Photosensitizers for Dye-Sensitized Solar Cells

Fluorenes are very attractive as π-conjugated spacers in dye-sensitized solar cells (DSSCs) due to its higher molar extinction coefficients and more red-shifted spectra as com-pared to biphenyl moieties.1 This is due to the co-planarity of two phenyl groups with the dialkyl group acting as a knot which could result in better π-conjugative properties, thus, larger charge-transfer transitions. The aggregation effect, which is caused by the increase planarity of the biphenyl group, can be controlled by introducing bulky alkyl groups at the 9,9-position of the fluorenyl moiety. A study of (9,9-diethyl-9H-fluorenyl)-based dye with increasing concen-tration of chenodeoxycholic acid (CDCA) as co-adsorbent showed that the short-circuit photocurrent density (JSC) drastically decreased with increasing chenodeoxycholic acid concentration but the open-circuit voltage (VOC) and fil