Recent advances in organic photovoltaics (OPVs) have shown promising alternatives to green energy, enabling cost-effective and lightweight substitutes to traditional silicon solar cells. The synthetic versatility of organic small molecules has driven small-molecule based OPVs to reach power conversion efficiency surpassing 8%. Boron dipyrromethene (BODIPY) dyes are a class of highly absorptive materials suitable for OPVs. A benzannulated BODIPY (bDIP) molecule exhibiting strong absorption at 640 nm is used as an electron donor with C60 as the acceptor. The BODIPY dye demonstrated the best performance in lamellar architecture (ITO/bDIP/C60/bathocuproine/Al), giving power conversion efficiency up to 4.5 %. The insensitivity of short-circuit current to bDIP thickness was probed by neutron reflectivity experiment. The analysis on reflectivity measurements suggests the presence of a mixed layer at the D/A interface in the bilayer device. bDIP and C60 exhibit a substantial amount of mixing, forming a 13 nm mixed layer when C60 was deposited onto a room temperature bDIP film. Planar-mixed heterojunction (PMHJ) devices were fabricated to understand the extent of spontaneous mixing between the donor and acceptor material. The native mixed region in the bilayer device was shown to most resemble a blended 1:3 bDIP:C60 layer in the structure:(ITO/bDIP/bDIP:C60 blend/C60/bathocuproine/Al). Our results show a discrete interface in lamellar devices cannot always be assumed to be present. A PMHJ-like picture may be a more realistic representation of our lamellar devices.

High efficiency BODIPY lamellar organic photovoltaics

249th National Meeting (2015)

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