Highly Efficient Indoor Organic Solar Cells by Voltage Losses Minimization through Fine-tuning of Polymer Structures

摘要： Herein we report a detailed study on the optoelectronic properties, photovoltaic performance, structural conformation, morphology variation, charge carrier mobility and recombination dynamics in bulk heterojunction (BHJ) solar cells comprising of a series of donor-acceptor (D-A) conjugated polymers as electron donors based on benzodithiophene (BDT) and 5,8-bis(5-bromothiophen-2-yl)-6,7-difluoro-2,3-bis(3-(octyloxy)phenyl)quinoxaline as a function of the BDT’s thienyl substitution (alkyl (WF3), alkylthio (WF3S) and fluoro (WF3F)). It is manifested the synergistic positive effects of the fluorine substituents on the minimization of the bimolecular recombination losses, the reduction of the series resistances (RS), the increment of the shunt resistances (RSh), the suppression of the trap-assisted recombination losses, the balanced charge transport, the finer nanoscale morphology and the deeper highest occupied molecular orbital (EHOMO) versus the alkyl- and alkylthio- substituents. According to these findings, WF3F:[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) based-organic photovoltaic (OPV) device is a scarce example that feature a high power conversion efficiency (PCE) of 17.34% under 500 lx indoor LED light with a high open-circuit voltage (VOC) of 0.69 V, due to the suppression of the voltage losses and a PCE of 9.44% at 1-sun (100 mW/cm2) conditions, simultaneously.