Effect of Cations in Coadsorbate on Charge Recombination and Conduction Band Edge Movement in Dye-Sensitized Solar Cells

This article quantitatively studied the coadsorption effect of deoxycholic acid (DCA) and sodium deoxycholate (DCNa) on the conduction band (CB) shift and charge recombination in dye-sensitized solar cells (DSSC). We found that the degree of the effect varied as the cation differed from H + to Na + . DCA shifted the CB positively by 26 mV, but DCNa shifted the CB negatively by 33 mV. As compared with the dye-alone-based DSSC, the coadsorption of dye NKX-2677 (2-cyano-3-[5′-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1 H,4 H,10 H -11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2′]bithiophenyl-5-yl]acrylic acid) with DCA retarded the charge recombination rate by 10-fold, corresponding to a 70 mV enhancement of the open-circuit photovoltage ( V oc ), and the coadsorption of NKX-2677 with DCNa slowed down the charge recombination rate by 3-fold, corresponding to a 37 mV enhancement of V oc . The suppression of charge recombination in combination with CB movement, arising from coadsorption, resulted in a V oc gain of 44 mV (= 70−26 mV) for the DSSC with NKX-2677/DCA and 70 mV (= 37 + 33 mV) for the DSSC with NKX-2677/DCNa. The experimentally observed V oc enhancements of 41 mV by DCA coadsorption and 65 mV by DCNa coadsorption were in good agreement with the calculated improvements.