Highly efficient quantum dot solar cells

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Poster, Lida Givalou, 222
Publication date: 5th February 2015

The replacement of transition metal complexes and organic dyes in third generation photovoltaics by low cost light harvesting materials has occupied the scientific interest during the recent decades. In this context, the use of quantum dots as photosensitizers, contributes to the preparation of efficient solar cells, which are known as Quantum Dot Sensitized Solar Cells (QDSSCs) [1]. The semiconductor quantum dots, with particle size of a few nanometers, exhibit big changes in their optoelectronic properties with respect to their bulk analogues, because of the quantum size effect. This particular behavior is due to its small particle size which is comparable to the de Broglie wavelength of the nanocrystalline semiconductor electrons. The result is the limitation of the delocalization of the electron cloud and the acquisition of discrete energy values of conduction and valence bands, with a parallel decrease of the corresponding energy gap. Because of the quantum confinement, the optical properties and the energy gap of nanocrystals can be varied depending on their size [2]. In the present study cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots are deposited on nanostructured titania (TiO₂) films to prepare core-shell (CdS/CdSe) sensitized photoelectrodes. The quantum dots were prepared by successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) techniques [3]. The experimental conditions and the steps followed in the above methods were chosen so that the size of the quantum dots be maintained in the range nm, wherein quantum phenomena are observed. The new materials have been incorporated in solar cells. For the manufacture of quantum dots solar cells, an aqueous solution based on the redox couple Na₂S/S was used as electrolyte (in order to regenerate the oxidized quantum dots), while CoS, CuS, Cu₂S and their mixtures prepared by chemical and electrochemical deposition were used as counter electrodes. The solar cells demonstrated power conversion efficiencies as high as 5.03%, which are among the highest values reported until now in the literature. This is mostly due to the successful combination of strong absorption of solar radiation by the quantum dots and optimum transfer of oxidized hole at the corresponding electrolyte/cathode electrode interface.

[1]Kamat,P.V. Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters. J. Phys. Chem. C 2008, 112, 18737–18753. [2]Barea, E.M.; Shalom, M.; Gimenez, S.; Hod, I.; Mora-Sero,I.; Zaban, A.; and Bisquert, J. Design of Injection and Recombination in Quantum Dot Sensitized Solar Cells. J. Am. Chem. Soc.2010, 132,6834–6839. [3]Sfaelou, S.; Kontos, A.G.; Givalou, L.; Falaras,P.; Lianos, P. Study of the stability of quantum dot sensitized solar cells. Catalysis Today 2014, 230, 221–226.

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