Effects of a dianion compound as a surface modifier on the back reaction of photogenerated electrons in TiO2-based solar cells

Abstract

The TiO2 films were modified with a dianion compound, 1,2-ethanedisulfonic acid disodium salt (ESD), to give a negative charge (ethane sulfonate anion) on the TiO2 surface, i.e., TiO2-O-SO2-CH2-CH2-SO3−), and effects of repulsion between the negative charge and ions (I3−) of the electrolyte on the performance of dye-sensitized solar cells (DSSCs) were investigated. The reference device without any modification showed a power conversion efficiency (PCE) of 9.89%, whereas for the device with ESD(20)-TiO2/FTO, which was prepared by soaking bare TiO2/FTO in an ESD solution for 20 min, the PCE was increased to 10.97%, due to an increase in both short-circuit current (Jsc) and open-circuit voltage(Voc). It was verified from the measurements of electrochemical impedance, open-circuit voltage decay and dark current that the enhancement in the Jsc and Voc values was attributed to the reduced back reaction between photoinjected electrons and I3− ions, resulting from the presence of the ethane sulfonate anions on the TiO2 surface.