Functionalized Graphene as an Electron-Cascade Acceptor for Air-Processed Organic Ternary Solar Cells

Functionalized graphene nanofl akes (GNFs) are used as an electron-cascade acceptor material in air-processed organic ternary bulk heterojunction solar cells. The functionalization is realized via the attachment of the ethylenedinitrobenzoyl (EDNB) molecule to the GNFs. Simulation and experimental results show that such nanoscale modifi cation greatly infl uences the density of states near the Fermi level. Consequently, the GNF-EDNB blend presents favorable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels to function as a bridge structure between the poly[ N -9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′- benzothiadiazole)] (PCDTBT) and the [6,6]-phenyl-C71-butyric-acid-methylester (PC 71 BM). The improved exciton dissociation and charge transport are associated with the better energy level alignment of the ternary blend and the high electrical conductivity of the GNFs, which act as additional electron transport channels within the photoactive layer. The resulting PCDTBT/GNFEDNB/ PC 71 BM ternary organic solar cells, fabricated entirely under ambient conditions, exhibit an average power conversion effi ciency enhancement of ≈18% as compared with the binary blend PCDTBT/PC 71 BM