Photovoltaic and transport properties of the heterojunction between poly (4,4′-dipentoxy-2,2′bithiophene) and n-doped silicon

Abstract

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.