Evaluation of carrier transport and recombinations in cadmium selenide quantum-dot-sensitized solar cells

In this paper, we present a study on cadmium selenide (CdSe) quantum-dot-sensitized solar cells (QDSSCs) in terms of the evaluation of carrier transport and recombinations using intensity-modulated photovoltage spectroscopy (IMVS) and intensity-modulated photocurrent spectroscopy (IMPS). Using the obtained data through this evaluation, we calculated the electron transport time (tau(sc)), electron recombination lifetimes (tau(oc)), effective diffusion constants (D-eff), and diffusion lengths (L-n). The QDSSC used in this study show improved fill factors (FF) of similar to 60% with a polysulfide (S2-/S-x(2-)) redox mediator and Pt counter electrode. This result is ascribed to the low series resistances (R-s) of QDSSC that are accessed by electrochemical impedance spectroscopy. In addition, the present study provides information on the sensitization mode of CdSe QDs on TiO2 electrodes, achieved by scanning transmission electron microscopy (STEM) combined with EDS imaging. (C) 2012 Elsevier B.V. All rights reserved.