Effect of Extended π‐Conjugation Structure of Donor–Acceptor Conjugated Copolymers on the Photoelectronic Properties

Abstract

New donor-acceptor conjugated copolymers based on alkylthienylbenzodithiophene (BDTT) and alkoxynaphthodithiophene (NDT) have been synthesized and compared with their benzo[1,2-b:4,5-b']dithiophene (BDT)-based analogues to investigate the effect of the extended π conjugation of the polymer main chain on the physicochemical properties of the polymers. A systematic investigation into the optical properties, energy levels, field-effect transistor characteristics, and photovoltaic characteristics of these polymers was conducted. Both polymers demonstrated enhanced photovoltaic performance and increased hole mobility compared with the BDT-based analogue. However, the BDTT-based polymer (with π-conjugation extension perpendicular to main chain) gave the highest power conversion efficiency of 5.07% for the single-junction polymer solar cell, whereas the NDT-based polymer (with π-conjugation extension along the main chain) achieved the highest hole mobility of approximately 0.1 cm(2) V(-1) s(-1) based on the field-effect transistor; this indicated that extending the π conjugation in different orientations would have a significant influence on the properties of the resulting polymers.