Significant enhancement in the power conversion efficiency of porphyrin based dye sensitized solar cell by co-sensitization with metal free dye

A step wise approach for co-sensitization of a zinc porphyrin sensitizer (Zn-por) with symmetrical BF2-azopyrrole dye (BF2) for dye sensitized solar cells (DSSCs) has been developed. With this approach, the co-sensitized Zn-por + BF2 based DSSC shows both J(sc) and V-oc significantly enhanced in relation to their individual sensitized DSSCs. Upon optimization, the DSSC sensitized with Zn-por + BF2 system yields J(sc) = 12.4 mA cm(-2), V-oc = 0.72 V, FF = 0.70, and PCE = 6.25%. This performance is superior to that of individual DSSC sensitized with Zn-por (PCE = 4.83%) and BF2 (PCE = 3.26%), respectively, under similar conditions. The broader IPCE spectra of the DSSC based on Zn-por + BF2 dye relative to other DSSCs are responsible for the higher J(sc). From the electrochemical impedance spectroscopy (EIS) data, we found that the charge recombination can be significantly retarded for co-sensitized system, relative to the Zn-por based DSSCs to account for the enhanced V-oc. The PCE is further enhanced by employing decoxycholic acid (DCA) as coadsorbent. The highest PCE obtained for DSSC with Zn-por and BF2 in the presence of DCA is about 7.46%. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794746]