Abstract
Quantum dots are drawing great attention as a material for the next-generation solar cells because of the high absorption coefficient, tunable band gap, and multiple exciton generation effect. In search of the viable way to enhance the power conversion efficiency of quantum dot-sensitized solar cells, we have succeeded in preparing the quantum dot solar cells with high efficiency based on CdSe:X (Mn2+ or Cu2+) nanocrystal by successive ionic layer absorption and reaction. The morphological observation and crystalline structure of photoanode were characterized by field-emission scanning electron microscopy, X-ray diffraction, and the EDX spectra. In addition, the electrochemical performance of photoelectrode was studied by the electrochemical impedance spectra. As a result, we have succeeded in designing QDSSCs with a high efficiency of 4.3%. Moreover, the optical properties, the direct optical energy gap, and both the conduction band and the valence band levels of the compositional CdSe:X were estimated by the theory of Tauc and discussed details. This theory is useful for us to understand the alignment energy structure of the compositions in electrodes, in particular, the conduction band and valence band levels of CdSe:X nanoparticles.
Highlights
In recent years, inorganic semiconductor materials, which are called Quantum Dots (QDs), have emerged as a powerful light-absorbing material that generates electrons for the quantum dot-sensitized solar cell (QDSSC) application
Various QDs were applied in the QDSSCs such as CdS, CdSe [1], PbS, PbSe [2, 3], and InP [1]
There are a number of ways to improve performance of QDSSCs such as QDSSCs based on the CdS/CdSe combination synthesized by chemical bath deposition methods and successive ionic layer absorption and reaction (SILAR) adsorbed directly onto TiO2 nanoparticles [12, 13]
Summary
Inorganic semiconductor materials, which are called Quantum Dots (QDs), have emerged as a powerful light-absorbing material that generates electrons for the quantum dot-sensitized solar cell (QDSSC) application. The combination of electrons and holes in the contact surfaces and in semiconductor oxides such as TiO2 and ZnO causes the reduction in performance of QDSSCs. To reduce the recombination processes, Jung and colleagues coated CdS QDs with a ZnS layer to protect QDs from the electrolyte [14,15,16]. The significant effects of X dopant on optical, physical, chemical, and photovoltaic properties of QDSSCs can be studied by the UV-Vis spectra and Tauc equation, which can determine the Eg, CB, and VB positions of X ions doped on pure CdSe nanoparticles This theory is useful for us to understand the alignment energy structure of the compositions in electrodes, in particular, CB and VB levels of CdS, CdSe:X nanoparticles. The electrochemical impedance spectra were carried out to determine dynamic resistances in QDSSCs
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