Increasing the open-circuit voltage and dielectric constant by introducing the number of fluorine atoms in organic solar cells

For the purpose of examining the influence of the number of fluorine atoms on the open-circuit voltage (VOC) in photoelectric devices, the polymers PBDT-0F-G, PBDT-2F-G, PBDT-4F-G were synthesized. These side chains of the polymer were substituted by fluorine atoms in different quantities and the photovoltaic properties were characterized. The introduction of F atoms on the side chain has a deeper molecular orbital energy level than the polymer without F atoms. Thus, the introduction 4 F atoms enhanced the VOC, with an increased to 0.97 V, compared with 0.95 V in the control device. In addition, fluoridation also improves the dielectric constant, especially when the side chain was enhanced by 4 fluorine atoms, the εr of PBDT-4F-G at 10 kHz was measured to be 4.5, which is higher than that of PBDT-2F-G (3.1) and PBDT-0F-G (2.9). Thus, the carrier mobility in the bulk heterojunction (BHJ) blends was improved. The results show that the improvement of devices performance is caused by introduction of F atoms.