Effect of Ultrathin Al2O3 Layer on TiO2 Surface in CdS/CdSe Co-Sensitized Quantum Dot Solar Cells

In order to enhance the photovoltaic property of the CdS/CdSe co-sensitized quantum dot sensitized solar cells (QDSSCs), the surface of nanoporous TiO2 photoanode was modified by ultrathin Al2O3 layer before the deposition of quantum dots (QDs). The Al2O3 layer, dip-coated by 0.10 M Al precursor solution, exhibited the optimized performance in blocking the back-reaction of the photo-injected electrons from TiO2 conduction band (CB) to polysulfide electrolyte. Transient photocurrent spectra revealed that the electron lifetime (tau(e)) increased significantly by introducing the ultrathin Al2O3 layer on TiO2 surface, whereas the electron diffusion coefficient (D-e) was not varied. As a result, the V-oc increased from 0.487 to 0.545 V, without appreciable change in short circuit current (J(sc)), thus inducing the enhancement of photovoltaic conversion efficiency (eta) from 3.01% to 3.38%.