Effect of mono- and di-anchoring dyes based on o,m-difluoro substituted phenylene spacer in liquid and solid state dye sensitized solar cells

Abstract

Novel mono- and di-anchoring organic dyes have been designed and synthesized with o,m-difluoro substituted phenylene spacer and were tested for DSSCs in presence of solid-state (SJE-4) as well as liquid (BMII) electrolytes. The new and simple structures of Cz-D1 and Cz-D2 dyes have same carbazole donor unit with either one or two side substitution of o,m-difluoro substituted phenylene π-spacer and cyanoacrylic acid acceptor. The photophysical and electrochemical properties of photosensitizes are investigated in detail and correlated with the solar cell performance. The Cz-D2 dye have ~20% higher device efficiency than Cz-D1 due to its lower LUMO level, and presence of two acceptor groups which provide efficient electron extraction from carbazole donor, lesser aggregation, high molar extinction coefficient and better charge transfer. Without using any additive, Cz-D2 exhibited an attractive power conversion efficiency (PCE) of 5.35% (Jsc = 10.38 mA/cm2, Voc = 0.75 V and FF = 0.60) in presence of iodide redox electrolyte. These dyes exhibit comparatively less efficiency when used to fabricate a solid state dye sensitized solar cell in presence of SJE-4 electrolyte due to aggregation between fluorine substituted phenylene spacer and electrolyte through strong H-bonding that might cause more electron recombination/back electron transfer. Good stability was also observed for both the dyes.