Organic Photovoltaic Devices Based On All-Fused-Ring Small Molecule Acceptors

All-fused-ring small molecules are a novel type of electron acceptor materials with excellent chemical stability,photostability and thermal stability,and thus possess broad prospects for application in the field of organic photovoltaic.Organic solar cells and photovoltaic organic photodetectors utilize the blends of organic polymer donor materials and acceptor materials as the active layer.The blended separation morphology of the donor and acceptor in the active layer plays an important role in the device performance.The blended morphology control of all-fused-ring small molecule acceptor materials is of great significance for the development of high performance organic solar cells and photovoltaic organic photodetectors.In this paper,based on the all-fused-ring small molecule acceptor materials,by changing the alkyl chain branching site of the all-fused-ring small molecule materials,the donor/acceptor blended phase separation morphology of the active layer is regulated,and thus the performance of organic solar cells gets improved.Besides,the effect of residual palladium contents in the polymer donor on the performance of photovoltaic organic photodetectors is investigated.The specific contents are as follows:1.For organic solar cell devices,we developed two all-fused-ring small molecule acceptors,FM5 and FM6,with different branching positions of alkyl chains on the pyrrole motif.The effect of branching points of the alkyl chains on optical and electronic properties,molecular stacking of the molecules has been investigated.Compared with FM5 with 2nd-position branched alkyl chains,FM6 with 3rd-position branched alkyl chains exhibits the blue-shifted absorption and higher crystallinity.Due to the large steric hindrance caused by alkyl chains at 2nd branching position,FM5 exhibits appropriate molecular aggregation and thus favorable film morphology in the blend film.Due to the suitable blend film morphology,the OSC device using FM5 as electron acceptor exhibits a power conversion efficiency(PCE)of 9.03%,which is higher than that of FM6(6.67%).2.For organic photodetector devices,in order to further reduce the dark current density,we used metal chelating agents to remove palladium from polymer donor D18.Before and after the removal of palladium by metal chelating agents,the residual palladium content in D18 was 66.33 ppm and 18.15 ppm,respectively,with a small difference,so the level of dark current density was similar as well.