Molybdenum trioxide thin film recombination barrier layers for dye sensitized solar cells

Abstract

A physical vapor deposition based molybdenum trioxide (MoO₃) thin film is demonstrated as an efficient reverse-electron recombination barrier layer (RBL) at the fluorine doped tin oxide (FTO)/titanium dioxide (TiO₂) interface in dye sensitized solar cells (DSSCs). Thin films of MoO₃ show an average optical transmittance of ∼77% in a spectral range of 350–800 nm with bandgap value of ∼3.1 eV. For an optimum thickness of MoO₃, deposited for 5 minutes, the resulting DSSCs showed 15% enhancement in efficiency (η) compared to the reference DSSC which did not use MoO₃ RBL; this suggests that MoO₃ is effectively suppressing interfacial recombination at the FTO/TiO₂ interface. Further, increasing the thickness of MoO₃ RBL at the FTO/TiO₂ interface (20 minutes deposition) is observed to impede charge transport, as noticed with 55% reduction in η compared to the reference DSSC. Thin film MoO₃ RBL with an optimum thickness value at the FTO/TiO₂ interface efficiently blocks the leaky transport pathways in the mesoporous TiO₂ nanoparticle layer and facilitates efficient charge transport as confirmed by electrochemical impedance spectroscopy.