Study on interfacial interactions and optoelectronic properties of MEH-PPV/SnO2 hetero-structure

Abstract

The exciton dynamics in nanocomposites of tin oxide (SnO2) nanoparticles with a conjugated polymer (poly (2-methoxy-5-(2'-ethylhexyloxy) 1,4-phenylenevinylene) (MEH-PPV) have been investigated by steady-state, time-resolved photoluminescence (PL) spectroscopy and cyclic voltammetry (CV) analysis. SnO2 is an air-stable, optically transparent, electrically conductive deep valance band metal oxide which is suitable as an electron-accepting material in organic photovoltaics (PVs). Results reveals that SnO2 is an efficient electron-accepting material in comparison with titanium dioxide (TiO2) nanoparticles. Efficient charge separation takes places at SnO2/MEH-PPV interfaces when the polymer is excited, leading to enhancement in quenching of PL efficiency (10%) and shortening of the measured PL lifetime. In addition, the reduction in recombination rate of MEH-PPV/SnO2 nanocomposite show that the incorporation of nanoparticles in the polymer chain reduce disorders in the polymer chains. The blue-shift in the absorbance and emission maxima denotes that the process of in situ polymerization resulted in shortening of polymer chain conjugation. The electrochemical analysis for MEH-PPV/SnO2 nanocomposite shows increase in current density compared to MEH-PPV/TiO2 and pristine MEH-PPV. Moreover, the PL degradation experiments showed that MEH-PPV/SnO2 exhibited enhanced stability. MEH-PPV/SnO2 film attained 50% of the original intensity in ∼10 d, while pristine MEH-PPV and MEH-PPV/TiO2 exhibited half-life of ∼5 d when exposed to an ambient environment. The effect of TiO2 nanoparticles to stabilize MEH-PPV is though less important than that of SnO2. Thus MEH-PPV/SnO2 nanocomposite with enhanced absorbance, conductivity, stability and lowered bandgap formed an effective type-II band structure suitable for the PV active layer.