Abstract
While polymer acceptors are promising fullerene alternatives in the fabrication of efficient bulk heterojunction (BHJ) solar cells, the range of efficient material systems relevant to the “all‐polymer” BHJ concept remains narrow, and currently limits the perspectives to meet the 10% efficiency threshold in all‐polymer solar cells. This report examines two polymer acceptor analogs composed of thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) and 3,4‐difluorothiophene ([2F]T) motifs, and their BHJ solar cell performance pattern with a low‐bandgap polymer donor commonly used with fullerenes (PBDT‐TS1; taken as a model system). In this material set, the introduction of a third electron‐deficient motif, namely 2,1,3‐benzothiadiazole (BT), is shown to (i) significantly narrow the optical gap (Eopt) of the corresponding polymer (by ≈0.2 eV) and (ii) improve the electron mobility of the polymer by over two orders of magnitude in BHJ solar cells. In turn, the narrow‐gap P2TPDBT[2F]T analog (Eopt = 1.7 eV) used as fullerene alternative yields high open‐circuit voltages (VOC) of ≈1.0 V, notable short‐circuit current values (JSC) of ≈11.0 mA cm−2, and power conversion efficiencies (PCEs) nearing 5% in all‐polymer BHJ solar cells. P2TPDBT[2F]T paves the way to a new, promising class of polymer acceptor candidates.
Alternating π‐conjugated polymers composed of electron‐deficient thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) and 3,4‐difluorothiophene ([2F]T) motifs are proving relevant as fullerene alternatives for “all‐polymer” bulk heterojunction (BHJ) solar cells. When a third electron‐deficient motif, namely 2,1,3‐benzothiadiazole (BT), is inserted in the main chain, the corresponding polymer (P2TPDBT[2F]T) yields a twofold increase in BHJ device efficiency.