Photoinduced charge carriers at surfaces and interfaces of poly[2−methoxy−5−(2′−ethyl−hexyloxy)−1,4−phenylenevinylene]with Au and GaAs

The electronic structure and photoinduced surface/interface charge transfer processes have been studied in $\mathrm{poly}[2-\mathrm{methoxy}{-5-(2\mathrm{}}^{\prime }-\mathrm{e}\mathrm{t}\mathrm{h}\mathrm{y}\mathrm{l}-\mathrm{h}\mathrm{e}\mathrm{x}\mathrm{y}\mathrm{l}\mathrm{o}\mathrm{x}\mathrm{y})-1,4-\mathrm{phenylene}\mathrm{}\mathrm{vinylene}]$ (MEH-PPV) thin films spin-coated on Au and n-GaAs(111) substrates using surface photovoltage spectroscopy. The results show that the MEH-PPV film is a p-type semiconductor with an optical band gap of around 2.1 eV and a surface work function of 4.7 eV, and its photovoltaic response is dominated by its free surface rather than the interface with the substrate. In addition, an acceptor surface state at 0.5 eV above the valence-band edge is found in films produced at low spinning rate, perhaps due to surface roughness. Efficient photoinduced electron injection from MEH-PPV films into the GaAs substrates is observed and found to have a strong dependence on the solvent used in the MEH-PPV spin deposition. These findings are discussed in view of the electronic and physical structure of the films.