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 investigated in the dark and under white illumination. The dark current-voltage characteristic and the impedance spectra suggest that the current is space charge limited at forward bias > 0.2 V, whereas it has an exponential trend for very low forward voltages. A Schottky barrier formation at the poly(ET2)/n-Si interface is demonstrated, The barrier height values, obtained both from the Mott-Shottky plot (0.80 eV) and from the dependence of the open-circuit voltage on the short-circuit current (0.77 eV), are in accord with the polymer redox potential. The short-circuit current is a linear function of the incident light intensity, as expected for silicon solar cells. The open-circuit voltage is quite low with respect to the calculated built-in potential of the junction, being lowered by the drop across the space charge layer. (C) 1998 Elsevier Science B.V. All rights reserved.