Fluorene-bridged organic dyes with di-anchoring groups for efficient co-adsorbent-free dye-sensitized solar cells

Abstract

A series of new fluorene-bridged organic dyes with di-anchoring groups have been synthesized and well characterized. Such a molecular design strategy using two organic anchors inhibits the undesirable charge recombination and prolongs the electron lifetime which results in significant enhancement of the power conversion efficiency (η). These findings were supported by the results from electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD). Under standard AM 1.5 irradiation (100 mW cm⁻²), the best dye-sensitized solar cell (DSSC) exhibits a high η of 6.11% without the need for co-adsorbent addition. An open-circuit photovoltage (V_oc) of 0.753 V, a short-circuit photocurrent density (J_sc) of 11.20 mA cm⁻² and a fill factor (ff) of 0.725 were measured in such co-adsorbent-free cells. The high V_oc value is mainly attributed to the improved electron lifetime (τ_n) and high resistance to the recombination of electrons (R_rec) of 422.38 Ω.