Statistical mechanics for solitons in the presence of electrons and their contributions to photovoltage in polyacetylene schottky barrier diodes

Abstract

Despite the evidence that solitons play an important role in the photoconductivity of trans-polyacetylene, it has been argued that the photovoltaic effect cannot be due to solitons. To examine the validity of this argument, I first obtain the relations between the chemical potentials of charged and neutral solitons and electrons and holes, showing in particular that the chemical potential of a charged soliton must be the same as that of the carrier of the same sign. The relations between the chemical potentials and the thermal equilibrium concentrations of neutral and charged solitons are derived. With these relations and the condition of charge neutrality the electron and hole concentrations can be calculated. Since most of the photovoltage data have been obtained on Schottky diodes, I then consider the role played by solitons in the process of barrier formation and the dark current-voltage characteristic. Using the results obtained for the chemical potentials of the solitons, I show that, on thermodynamic grounds, the observed photovoltage can be explained as well by a soliton mechanism as by free electrons and holes.