Efficient Eosin Y Dye-Sensitized Solar Cell Containing Br-/Br3- Electrolyte

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Abstract
We found that Br-/Br3- is more suitable than an I-/I3- couple in dye-sensitized solar cells in terms of higher open-circuit photovoltage (Voc) production and higher overall energy conversion efficiency (η) if the dye sensitizer has a more positive potential than that of Br-/Br3-. Under simulated AM1.5 one sun, an eosin Y dye-sensitized solar cell containing 0.4 M LiBr + 0.04 M Br2 electrolyte in acetonitrile yielded a short-circuit photocurrent (Jsc) of 4.63 mA cm-2, Voc of 0.813 V, and fill factor (FF) of 0.693, corresponding to 2.61% of η. Under the same conditions except for the electrolyte 0.4 M LiI + 0.04 M I2 in acetonitrile instead, the device produced 1.67% of η (Jsc = 5.15 mA cm-2, Voc = 0.451 V, FF = 0.721). Replacement of I-/I3- with Br-/Br3- in eosin Y dye-sensitized solar cells yielded a significant increase in Voc offset by slight decreases in Jsc and FF, leading to an increase in η by 56%. The significant gain in Voc was attributed to the enlarged energy level difference between the redox potential of the electrolyte and the Fermi level of TiO2 and the suppressed charge recombination as well. The rate for charge recombination between bromine and the injected electrons was determined to be first order in bromine.