Donor-Acceptor Shape Matching Drives Performance in Photovoltaics

• Published in: Advanced energy materials Vol. 3; no. 7; pp. 894 - 902
• Main Authors: Schiros, Theanne, Kladnik, Gregor, Prezzi, Deborah, Ferretti, Andrea, Olivieri, Giorgia, Cossaro, Albano, Floreano, Luca, Verdini, Alberto, Schenck, Christine, Cox, Marshall, Gorodetsky, Alon A., Plunkett, Kyle, Delongchamp, Dean, Nuckolls, Colin, Morgante, Alberto, Cvetko, Dean, Kymissis, Ioannis
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-07-2013; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Acceptors (electronic); Buckminsterfullerene; Donors (electronic); Efficiency; Electron transfer; Excitation; Fullerenes; organic electronics; Photovoltaic cells; Self assembly; self-assemblies; Solar cells; supramolecular materials
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201201125

While the demonstrated power conversion efficiency of organic photovoltaics (OPVs) now exceeds 10%, new design rules are required to tailor interfaces at the molecular level for optimal exciton dissociation and charge transport in higher efficiency devices. We show that molecular shape‐complementarity between donors and acceptors can drive performance in OPV devices. Using core hole clock (CHC) X‐ray spectroscopy and density functional theory (DFT), we compare the electronic coupling, assembly, and charge transfer rates at the interface between C60 acceptors and flat‐ or contorted‐hexabenzocorone (HBC) donors. The HBC donors have similar optoelectronic properties but differ in molecular contortion and shape matching to the fullerene acceptors. We show that shape‐complementarity drives self‐assembly of an intermixed morphology with a donor/acceptor (D/A) ball‐and‐socket interface, which enables faster electron transfer from HBC to C60. The supramolecular assembly and faster electron transfer rates in the shape complementary heterojunction lead to a larger active volume and enhanced exciton dissociation rate. This work provides fundamental mechanistic insights on the improved efficiency of organic photovoltaic devices that incorporate these concave/convex D/A materials.
Shape‐complementarity of donor and acceptor molecules drives self‐assembly into an extended interface with a ball‐and‐socket structural motif, which increases both the active volume and exciton dissociation rates to improve the efficiency of organic solar cells.