Sensitized solar cell from type-II CdTe/CdSe core/shell nanocrystals synthesized without seed purification at low temperature

Abstract

Quicker and simpler chemical fabrication route is always desirable for synthesis of technologically important nanocrystals. Here we propose simple aqueous method for synthesis of type-II heterostructure of CdTe/CdSe core/shell nanocrystals without purification of CdTe seed at a relatively lower temperature of ∼80 °C. These core/shell nanocrystals show structural and optical properties comparable to the nanocrystals synthesized using purified CdTe seed nanocrystals. Longer photoluminescence lifetime with thicker shells are observed in such CdTe/CdSe core/shell heterostructures grown by both procedures which indicates more non-radiative decay channels are being added with increasing thickness of shell layer. Sensitized solar cells are fabricated using these good quality unpurified core/shell nanocrystals. We found that efficiency of solar cell is a strong function of shell thickness as the charge carrier separation is also function of shell thickness in these type-II heterostructure nanoparticles. The increment in short circuit current density in nanocrystals having thickest shell is ∼300% compared to the core–shell nanocrystals having the thinnest shell prepared by us. We also found that sintering of photo-anode sensitized with these CdTe/CdSe nanocrystals is very important for achieving higher efficiency. Calculated maximum efficiency of the solar cell fabricated using core/shell nanocrystals with thickest CdSe shell is ∼2% with JSC = 8.9 mA/cm2 and VOC = 0.53 V.