Anode Modification Of Graphene And Its Application In Organic Photovoltaic Cells

As one of two-dimensional(2D)nanomaterials,graphene is a single sheet of hexagonally arranged sp~2-hybridized carbon atoms.It has been extensively studied in the field of optoelectronic devices due to its unique optical,electronic and mechanical properties.In this paper,graphene is applied into organic photovoltaic device(OPV)as a novel transparent electrode.In this thesis,monolayer graphene synthesized by chemical vapor deposition(CVD)method was used.And it was transferred from copper foil to a target substrate via a wet transfer route using polymethyl methacrylate(PMMA)as a supporting layer.The organic photovoltaic devices were successfully fabricated by spin-coating the active layer blend solution onto a 40 nm thick PEDOT:PSS-coated graphene electrode.However,the power conversion efficiency was sacrificed due to the mismatch between the work function of graphene and the Highest Occupied Molecular Orbital energy level of hole transport layer and hydrophobic intristic property of graphene.In this paper,several materials were used to modify graphene.It was found that copper oxide can be used as p-type dopant to modify graphene.And its water contact angle is also decreased,which allows PEDOT:PSS to spread on the surface of graphene effectively.Meanwhile,the work function of graphene was increased from 4.45 to 4.76 e V after Cux O modification.After that,the Cux O modified graphene was applied as anode into poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5–b?]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate]:[6,6]-phenyl-C71-butyric acid methyl ester(PCE-10:PC71BM)-based bulk heterojunction OPVs,and the PCE was enhanced from 4.00±0.44 to 5.23±0.47%.In order to further improve device performance,a small molecule 1,2,5-thiadiazole-fused 12-ring polyaromatic hydrocarbon(DNNBT-C12)with highly contorted conformation was further introduced into the active layer,forming a ternary blend polymer solar cell.The results showed that the PCE is further increased to 6.03±0.53% due to the improved light absorption of the active layer and enhanced recombination resistance in devices with this small molecular material induced.