Incorporating Se atoms to organoboron polymer electron acceptors to tune opto-electronic properties

Abstract

Conjugated polymers containing boron−nitrogen coordination bond (B←N) represent an important kind of polymer electron acceptors for all-polymer solar cells (all-PSCs). To improve the photovoltaic performance of all-PSCs, opto-electronic properties of polymer electron acceptors containing B←N need to be finely tuned. In this work, based on the alternating copolymer (PBN-12) of double B←N bridged bipyridine (BNBP) unit and 4,7-dithienyl-2,1,3-benzothiadizole unit, we report three new organoboron polymers by replacing the three S atoms in PBN-12 with Se atoms. With the increasing number of Se atoms, the organoboron polymers exhibit downshifted LUMO energy levels, upshifted HOMO energy levels, decreased bandgaps and redshifted absorption spectra. Among the three polymers, the polymer with two Se atoms exhibits the highest electron mobilities. All-PSCs devices with these organoboron polymers as electron acceptors exhibit an encouraging power conversion efficiency (PCE) of 5.4% with open-circuit voltage higher than 1.0 V. These results indicate an effective approach to finely tune opto-electronic properties of organoboron polymers towards opto-electronic device applications.