FBR (CAS number 1644381-95-2) having a similar AA-D-AA type structure to IDFBR, contains electron-donating alkylated fluorene as the core, flanked by electron withdrawing benzothiadiazole (BT) and 3-ethylrhodanine units on the periphery terminals.
FBR reduces the tendency of crystallization and helps to prevent the formation of large crystalline domains in the BHJ donor/acceptor blend composition leading to better device performance efficiency and longer life-times.
Comparing to PC71BM, FBR has a relatively high lowest unoccupied molecular orbital (LUMO) which in theory should give a higher open voltage (Voc). This is indeed the case for polymer organic solar cells with PffBT4T-2DT as the polymer donor and FBR as the electron acceptor, yielding a device performance efficiency over 7.8% with an open voltage of 1.12 eV. This is one of the highest achieved open voltages for polymer organic solar cells.
Device structure: ITO/ZnO/PffBT4T-2DT:FBR/MoOx/Ag [1]