Photovoltage and photoconductivity in Si/organic film/metal structures with films made of poly(3-alkylthiophene) molecules and polycyclic conjugated molecules

Photovoltage and photoconductivity in sandwich thin films devices based on cast regio-regular poly(3-dodecylthiophene) and multilayer LB corbathiene films were experimentally studied. n-Si and p-Si substrates and Al and Au top electrodes were used in the devices. Photovoltage values attained 0.6 V and photocurrents were 10 times bigger than dark currents under monochromatic visible light irradiation with total energy density less than 0.1 mW/cm2. The most pronounced photoresponse component was observed in the incident quanta range around 1.5 eV but only for the devices with n-Si substrate. This fact was accounted for by photovoltaic processes in the chemically formed film/n-Si interface where a negative electric charge is captured. Photovoltage vs. light intensity dependencies measured are in good agreement with this concept. Photovoltage and photoconductivity spectra of LB corbathiene film-based devices have a less pronounced peak corresponding to the filmsʹ π–π* transitions. A less pronounced peak in the spectra of poly(3-dodecylthiophene) film-based devices has a shift below the filmsʹ π–π* transition energy. That may indicate possible bipolaron formation in the polymer material. The data are further interpreted in terms of energy band diagrams of the devices.