PHOTOVOLTAIC AND TRANSPORT-PROPERTIES OF THE HETEROJUNCTION BETWEEN POLY(4,4'-DIPENTOXY-2,2'BITHIOPHENE) AND N-DOPED SILICON

The electrical characteristics of the junction obtained by depositing poly(4,4'-dipentoxy-2,2'-bithiophene) on n-type silicon have been inve stigated in the dark and under white illumination. The dark current-vo ltage characteristic and the impedance spectra suggest that the curren t is space charge limited at forward bias > 0.2 V, whereas it has an e xponential trend for very low forward voltages. A Schottky barrier for mation at the poly(ET2)/n-Si interface is demonstrated, The barrier he ight values, obtained both from the Mott-Shottky plot (0.80 eV) and fr om the dependence of the open-circuit voltage on the short-circuit cur rent (0.77 eV), are in accord with the polymer redox potential. The sh ort-circuit current is a linear function of the incident light intensi ty, as expected for silicon solar cells. The open-circuit voltage is q uite low with respect to the calculated built-in potential of the junc tion, being lowered by the drop across the space charge layer. (C) 199 8 Elsevier Science B.V. All rights reserved.