The effects of the number of anchoring groups and N-substitution on the performance of phenoxazine dyes in dye-sensitized solar cells

• Effects of N-substituent and additional anchor introduced to a phenoxazine donor.
• Increase of short-circuit current by increasing electron pathways and extending conjugation.
• Increase of open-circuit voltage by suppressing charge recombination.
• The best conversion efficiency was shown by a cell based on the mono-anchoring dye with an N-methoxyphenyl ring.

Four novel phenoxazine-based organic sensitizers were synthesized and applied to dye-sensitized solar cells. Cyanoacrylic acid as an additional anchoring group was introduced to the phenoxazine for efficient electron extraction from the donor part, and an N-substituent was added to suppress dye aggregation. The photophysical, electrochemical and photovoltaic properties of the solar cells based on these dyes were investigated to study the effects of these substituents on the performance of the dye-sensitized solar cells. The additional cyanoacrylic acid acceptor improved the short-circuit current because it widened the absorption ranges of the dyes, although it also increased the recombination rate. The N-methoxyphenyl unit decrease charge recombinations, resulting in higher open-circuit voltage. However, the bulky substituent decreased the amount of dye absorbed on the TiO2. As a result, the fabricated cells with the four dyes exhibited similar overall conversion efficiencies and, of these cells, the solar cell based on the N-4-methoxyphenyl mono-cyanoacrylate substituted dye showed the highest conversion efficiency of 5.09% (short-circuit current = 10.11 mA/cm2, open-circuit voltage = 690 mV, fill factor = 72.23%, an overall conversion efficiency = 5.09% under AM 1.5G conditions).