12 October 2009 Influence of alumina coating on transport and recombination in DSSCs with 1-methylbenzidazole as electrolyte additives
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Nanocrystalline TiO2 electrodes have been coated with alumina by being immersed into the solutions of aluminum isopropoxide and aluminum acetylacetonate respectively. The current-voltage characteristics of the TiO2 and TiO2/Al2O3 electrodes with 1-methylbenzimidazole (MBI) as additives in the electrolytes have been detected. It is found that the TiO2/Al2O3 electrodes immersed in the solutions of aluminum isopropoxide (acetylacetone as coordinate ligands) for 1 hour have obtained great increase of Jsc, and owned the improved cells efficiency by 17%. To discover the origins of this improved photovoltaic performance and investigate the electron properties of the cells, the electrochemical impedance spectroscopy (EIS) has been used both in the dark and under illumination at different applied potentials. It is proposed that with the coating of Al2O3, the adsorption of MBI cations at the surface of TiO2 electrodes decreased with the decrease of the applied potentials, which resulted in the downwards shift of the conduction band position of the TiO2/Al2O3 electrodes at the lower potentials. As a result, the charge transfer resistance Rct decreased, and chemical capacitance Cfilms increased. Under illumination, the decrease of Rct became smaller and the conductivities became larger, which was attributed to the recombination inhibition effect of Al2O3 coating to the photoinjected electrons. As a consequence, the electron lifetime and the effective diffusion length for the TiO2/Al2O3 electrodes increased, leading to the great increase of Jsc. It is indicated that with the coating of Al2O3, the decrease of Jsc could be overcome when MBI is used as the additives of the electrolyte.
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Xueqing Xu, Eva Maria Barea, Francisco Fabregat-Santiago, Juan Bisquert, Gang Xu, "Influence of alumina coating on transport and recombination in DSSCs with 1-methylbenzidazole as electrolyte additives", Proc. SPIE 7518, Photonics and Optoelectronics Meetings (POEM) 2009: Solar Cells, Solid State Lighting, and Information Display Technologies, 75180J (12 October 2009); doi: 10.1117/12.843448; https://doi.org/10.1117/12.843448

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