Comparative Photovoltaic Study of Physical Blending of Two Donor–Acceptor Polymers with the Chemical Blending of the Respective Moieties

Abstract

A regularly alternating terpolymer and a random terpolymer were synthesized from the constituent units of two donor–acceptor polymers with complementary absorption. They were then compared to a physical blend of these two donor–acceptor polymers in order to investigate the best means of extending the light absorption range in bulk heterojunction (BHJ) solar cells. While all three methods broadened the light absorption, the physical blend provided the best improvement in power conversion efficiency (4.10% vs 3.63% and 2.67% for the random and regular terpolymers, respectively). This is due to the increase in aggregation in the physical blend, as demonstrated in the UV–vis spectra, which likely leads to higher local mobility and less recombination. This study shows that in order to effectively increase the light absorption (and therefore performance) of a polymer:fullerene based BHJ solar cell, a terpolymer must retain a structure which allows sufficient aggregation.