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 f ilms were experimentally studied, n-Si and p-Si substrates and Al and Au to p electrodes were used in the devices. Photovoltage values attained 0.6 V a nd photocurrents were 10 times bigger than dark currents under monochromati c 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. T his fact was accounted for by photovoltaic processes in the chemically form ed film/n-Si interface where a negative electric charge is captured. Photov oltage 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-dodecy lthiophene) film-based devices has a shift below the films' pi-pi* transiti on energy. That may indicate possible bipolaron formation in the polymer ma terial. The data are further interpreted in terms of energy band diagrams o f the devices. (C) 1999 Elsevier Science S.A. All rights reserved.