Photogenerated charge carrier transport in p-polymer n-polymer bilayer structures

Abstract

We investigate polymer bilayer structures that can be utilized effectively for efficient photovoltaic properties. The transport characteristics of photogenerated free charge carriers across the interface of a bilayer consisting of p-type polymer poly(3-octyl thiophene) (P3OT) or poly(2- methoxy, 5-(2-ethylhexoxy)-1, 4-phenylene vinylene) (MEHPPV) and n-type polymer poly(benzamidazobenzo phenanthroline) (BBL) are studied using photocurrent spectral response, intensity modulated photocurrent spectra, current-voltage, and thermally stimulated current measurements. The parameters governing the device efficiency are controlled by the interfacial defect characteristics and electric field redistribution in the device. A clear evidence of these defect states at the polymer-polymer interface is revealed using the time and frequency domain photocurrent measurements. We compare the figure of merits of the P3OT/BBL and MEHPPV/BBL structures and correlate these properties to the interfacial processes.