Study of interfaces and cell geometries in quantum dot sensitized solar cells
Stavroula Sfaelou a, Nikolaos Balis a, Polycarpos Falaras b, Athanassios Kontos b, Panagiotis Lianos c
a Engineering Science Dept., University of Patras - Greece, Patras, Greece
b NCSR Demokritos, Division of Physical Chemistry, 153 10 Aghia Paraskevi Attikis, Athens, Greece
c FORTH/ICE-HT, Greece
Oral, Panagiotis Lianos, presentation 010
Publication date: 1st April 2013

Quantum dot sensitized solar cells (QDSSCs) enjoy increasing popularity [1,2] as a serious alternative to their dye-sensitized homologues.  A quantum dot (QD) sensitizer can be any small size semiconductor where quantum confinement effects demonstrate themselves by an important change in the energy band gap and subsequent modification of the light absorption threshold. However, the term usually refers to a few metal chalcogenides like CdS, CdSe, ZnS  and  PbS.  Combination of these QDs can offer panchromatic sensitization and  exploitation of the solar spectrum. Most importantly, combination of  semiconductors offers structures, which guarantee greater stability while they increase efficiency by inducing photogenerated charge carrier separation.  A well established efficient combination of QDs involves CdS and CdSe together with a ZnS passivation layer on the top. Many aspects of this combination have been thoroughly studied in the past  but open questions are still on stage [3]  and make an interesting subject of research.

In this presentation, we will present our recent experience on the study of combined CdS-CdSe-ZnS QD sensitizers of nanoparticulate titania as applied to liquid electrolyte QDSSCs. Particular emphasis will be placed on the study of semiconductor interfaces by several spectroscopic techniques including micro-Raman.  The order of materials deposition and mixing and the effect of annealing, the latter not being sufficiently stressed in literature, will be examined as important parameters greatly affecting cell efficiency.

Even though, most of our results are being obtained with photoanodes carrying nanoparticulate titania, some other forms of nanostructured titania will be critically examined in an effort to set off  their advantages and disadvantages. 

Finally, a typical liquid electrolyte QDSSC is made of a photoanode and a counter electrode separated by a thin thermoplastic gasket of thickness of a few tens of micrometers, similarly to their dye-sensitized homologues.  We consider this geometry too restrictive.  This geometry is understandable  in the case of dye-sensitized solar cells, which utilize organic electrolytes with small ionic conductivity.  In the case of QDSSCs, which employ aqueous polysulfide electrolytes  with high ionic conductivity, other cell geometries can be envisaged and will be discussed.

[1] Sudhagar P et al. Interfacial engineering of quantum dot-sensitized TiO2 fibrous electrodes for futuristic photoanodes in photovoltaic applications. J. Mater. Chem., 2012,22, 14228-14235 [2] Kamat P.V. Boosting the Efficiency of Quantum Dot Sensitized Solar Cells through Modulation of Interfacial Charge Transfer. Acc.Chem.Res. 2012, 45, 1906–1915
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