Impact of hydroxy and octyloxy substituents of phenothiazine based dyes on the photovoltaic performance

• Two novel dyes based on phenothiazine with extension of phenol and octyloxyphenyl units were synthesized.
• The dye with octyloxy unit exhibits stronger electron donor–acceptor strength as compared to the dye with hydroxy unit.
• The dye with octyloxy unit has higher electron lifetime and resistance of recombinations.
• The device based on the dye with octyloxy delivers η of 6.32% while the device based on the dye with hydroxy delivers η of 5.23%.

Two novel organic dyes containing hydroxy and octyloxy substituents onto a phenothiazine skeleton were synthesized and their effects on the photovoltaic performance were studied. Hydroxy acts as an ancillary anchoring unit along with the carboxylic group, while the phenothiazine modified moiety acts as an electron donor. The photophysical and electrochemical studies revealed that maximum absorbance of the dye with the hydroxy group in the solution was blue shifted and its band gap increased, indicating that donor acceptor strength was reduced as compared to the octyloxy substituted dye. Furthermore, electron lifetime of the organic dye with the hydroxy moiety was shorter due to smaller resistance of electron recombination. Contrarily the dye with octyloxy moiety exhibited higher electron lifetime and open-circuit photovoltage leading to an overall power conversion efficiency of 6.32% under standard AM 1.5G illumination. The IPCE was over 80% in the region between 450 and 500 nm.

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