Effect of end groups on fluorene based dyes without carboxyl anchors as efficient co-sensitizer for retarding charge recombination in DSSC applications

Abstract

Herein, simple A- π-D- π-A type fluorene-based metal-free organic dyes denoted as DICTF and DRCTF, carrying different terminal units without carboxylic acid were synthesize and utilizes as effective co-sensitizer. By tuning the electron-accepting cyanated terminal units in the dyes, their photo physical, electrochemical and photovoltaic properties were investigated. After stepwise co-sensitization of TiO2 photoanode with DRCTF/N-719 shows a PCE (Power Conversion Efficiency) of 8.22% which is higher than that of bare N-719 alone (4.23%) or higher than for the device co-sensitized with DICTF/N-719 (6.54%). The PCE of the N-719 dye is improved by co-sensitization with the dyes DICTF and DRCTF, clearly reflects in both short circuit current and open-circuit voltage results. EIS (Electrochemical Impedance Spectroscopy) analysis reveals the slow recombination kinetics and extended electron life time of the co-sensitized devices compared with N-719 dye-sensitized alone. Hence, a new stepwise co-sensitization strategy has been implemented in which, the main sensitizer has carboxyl anchors and the co-sensitizer does not have an anchoring group. This helps to boost the performances in the DSSC (Dye sensitized solar cells) by receiving panchromatic absorption and reducing the dye aggregation caused wherein N-719 dye is co-sensitized with DICTF or DRCTF.