Exciton diffusion length and concentration of holes in MEH-PPV polymer using the surface voltage and surface photovoltage methods

Abstract

Novelized method of the surface photovoltage (SPV) measurement convenient for evaluation of exciton diffusion length and thickness of the space charge region (SCR) in organic semiconductors is applied to poly[2-methoxy-5-(2′- ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) polymer. Exciton diffusion length and thickness of the SCR was found. The experiment is complemented by measurements of surface potential by the Kelvin probe force microscopy yielding the work function and concentration of free holes. The latter value is much lower than the concentration of ionized states determined from the thickness of the space charge region, which can be ascribed to the presence of traps. © 2012 Elsevier B.V. All rights reserved.