PbS quantum dot-sensitized solar cells (QDSCs) with a photovoltaic conversion efficiency (η) of 5.73% have been fabricated by applying Au/CuS/FTO as a counter electrode (CE), post-annealing the deposited PbS QDs, and introducing the bilayered TiO2 nanostructure as a photoanode.

Ultrathin SnO(2) layers were deposited on FTO substrate by the layer-by-layer (LbL) self-assembly technique utilizing negatively charged 2.5 nm sized SnO(2) nanoparticles (NPs) and cationic poly(allylamine hydrochloride) (PAH). For the construction of dye-sensitized solar cells (DSC), the bulk TiO(2) layer was deposited over the (PAH/SnO(2))(n) (n = 1-10) and subsequently calcined at 500 °C to remove organic components. With introducing four layers of self-assembled SnO(2) interfacial layer (IL), the short circuit current density (J(sc)) of DSCs was increased from 8.96 to 10.97 mA/cm(2), whereas the open circuit voltage (V(oc)) and fill factor (FF) were not appreciably changed. Consequently, photovoltaic conversion efficiency (η) was enhanced from 5.43 to 6.57%. Transient photoelectron spectroscopic analyses revealed that the ultrathin SnO(2) layer considerably increased the electron diffusion coefficient (D(e)) in TiO(2) layer, but the electron lifetime (τ(e)) was decreased unexpectedly. The observed unusual photovoltaic properties would be caused by the unique conduction band (CB) location of the SnO(2), inducing the cascadal energy band matching among the CBs of TiO(2), SnO(2), and FTO.

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