Molecular engineering of panchromatic unsymmetrical squaraines for dye-sensitized solar cell applications

Three unsymmetrical squaraine dyes JK-64, JK-65, and JK-64Hx, containing a bulky spirobifluorene or hexyloxyphenyl unit are designed and synthesized. These sensitizers, when anchored onto a TiO2 surface, exhibit decreased aggregation as well as enhanced unidirectional flow of electrons. Under standard global AM 1.5 solar conditions, an optimized JK-64Hx sensitized cell gave a short-circuit photocurrent density (Jsc) of 12.82 mA cm−2, an open-circuit voltage (Voc) of 0.54 V and a fill factor (ff) of 0.75, corresponding to an overall conversion efficiency (η) of 5.20%.