title: Semiconductor Quantum Dot Sensitized Solar Cells Based on Ferricyanide/Ferrocyanide Redox Electrolyte Reaching an Open Circuit Photovoltage of 0.8 V.
abstract: Semiconductor quantum dot sensitized solar cells (QDSSCs) have rapidly been developed, and their efficiency has recently exceeded 9%. Their performances have mainly been achieved by focusing on improving short circuit photocurrent employing polysulfide electrolytes. However, the increase of open circuit photovoltage (VOC) cannot be expected with QDSSCs based on the polysulfide electrolytes owing to their relatively negative redox potential (around -0.65 V vs Ag/AgCl). Here, we demonstrate enhancement of the open circuit voltage by employing an alternative electrolyte, ferricyanide/ferrocyanide redox couple. The solar cell performance was optimized by investigating the influence of ferricyanide and ferrocyanide concentration on their interfacial charge transfer and transport kinetics. The optimized ferricyanide/ferrocyanide species concentrations (0.01/0.2 M) result in solar energy conversion efficiency of 2% with VOC of 0.8 V. Since the potential difference between the TiO2 conduction band edge at pH 7 and the electrolyte redox potential is about 0.79 V, although the conduction band edge shifts negatively under the negative bias application into the TiO2 electrode, the solar cell with the optimized electrolyte composition has nearly reached the theoretical maximum voltage. This study suggests a promising method to optimize an electrolyte composition for maximizing solar energy conversion efficiency.
authors.affiliation: School of Engineering, RMIT University , Bundoora, Victoria 3083, Australia.
authors.forename: Rosemarie M
authors.initials: RM
authors.lastname: Evangelista
authors.affiliation: School of Engineering, RMIT University , Bundoora, Victoria 3083, Australia.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Makuta
authors.affiliation: School of Engineering, RMIT University , Bundoora, Victoria 3083, Australia.
authors.forename: Shota
authors.initials: S
authors.lastname: Yonezu
authors.affiliation: School of Engineering, RMIT University , Bundoora, Victoria 3083, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Andrews
authors.affiliation: School of Engineering, RMIT University , Bundoora, Victoria 3083, Australia.|Office for University-Industry Collaboration, Osaka University , 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.|Japan Science and Technology Agency (JST) , PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tachibana
keywords: CdS; ferrocyanide/ferricyanide redox couple; photovoltage decay; semiconductor quantum dots sensitized solar cells; transient photocurrent