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/cm(2). 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 films' pi-pi* transitions. A less pronounced peak in the spectra of poly(3-dodecylthiophene) film-based devices has a shift below the films' pi-pi* 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. (C) 1999 Elsevier Science S.A. All rights reserved.