Cosensitization of dye sensitized solar cells with a thiocyanate free Ru dye and a metal free dye containing thienylfluorene conjugation

Abstract

A stepwise approach has been applied for the cosensitization of a thiocyanate free Ru sensitizer (SPS-01) with a metal free dye containing thienylfluorene conjugation (JD1) for dye sensitized solar cells (DSSCs). The cosensitized SPS-01 + JD1 based DSSC showed a significant enhancement in both the open circuit voltage (V_oc) and the short circuit current (J_sc) relative to the individual single dye based DSSCs. The DSSC based on the SPS-01 + JD1 system yielded a J_sc of 15.38 mA cm⁻², a V_oc of 0.72 V, a fill factor (FF) of 0.76 and a power conversion efficiency (PCE) of 8.30%. This performance was superior to that of the DSSCs sensitized with the individual dyes SPS-01 (PCE = 5.98%) or JD1 (PCE = 4.76%) fabricated under the same conditions. Results show that the JD1 dye effectively overcomes the competitive light absorption by I₃⁻/I⁻ and also prevents dye aggregation and reduces the charge recombination. To understand the effects of the charge recombination of the injected electrons with I₃⁻ in the electrolyte, the dark current–voltage characteristics and electrochemical impedance spectra of the DSSCs sensitized with the SPS-01 and SPS-01+JD1 systems were measured. It was observed that the recombination of the electrons in the conduction band with I₃⁻ in the electrolyte in the DSSC sensitized with SPS-01 +JD1 was significantly reduced relative to the DSSC based on SPS-01.