Acceptor-acceptor-type Organoboron Conjugated Polymers: Effect of Backbone Configuration on Thermoelectric Performance

The development of n-type polymer thermoelectrics lags far behind that of p-type ones in view of material diversity and performance.New structural insights into the thermoelectric performance are needed for efficient n-type polymer thermoelectric materials. Herein, we developed three acceptor-acceptor type organoboron polymers and investigated the effect of backbone configuration on thermoelectric performance. The three polymers are designed based on double B←N bridged bipyridine(BNBP) unit with monomeric thieno[3,4-c]pyrrole-4,6-dione(TPD), TPD dimer and TPD trimer as the copolymerizing units, respectively. The three polymers show similar low LUMO energy levels but different backbone configuration. Compared with the wavy backbone configuration, the pseudo-straight backbone configuration imparts the polymer with much enhanced crystallinity and electron mobility. As a result, after n-doping, the polymer with pseudo-straight configuration shows much higher electronic conductivity and power factor. We think these findings could serve as important guidelines for molecular design toward efficient n-type polymer thermoelectric materials.