Hydrogen bond directed assembly of oligothiophene/fullerene superstructures on Au(1 1 1)

Abstract We previously reported that a branched quaterthiophene donor chromophore functionalized with a phthalhydrazide hydrogen bonding (H-bonding) unit ( MeBQPH ) gives twofold more efficient bulk heterojunction organic solar cells (with C 60 acceptors) compared to a nearly identical donor incapable of H-bonding ( MeBQPME ). Here, scanning tunneling microscopy (STM) studies confirm the formation of MeBQPH trimer rosettes on Au(1 1 1) through phthalhydrazide H-bonding interactions that are sufficiently strong to compete with adsorbate/substrate interactions. The MeBQPME comparator molecule void of hydrogen bonding functionality does not similarly assemble on the metal surface. Complementary density functional theory (DFT) calculations facilitate a structural understanding of the MeBQPH donor assemblies and their strong stabilization through formation of six hydrogen bonds. STM studies also reveal the templated growth of C 60 on ordered MeBQPH monolayers with C 60 molecules preferentially occupying the threefold interstitial sites of the MeBQPH monolayer. This work supports the idea that H-bonding interactions can be used to control the morphology of organic donor–acceptor blends to potentially create efficient and stable bulk heterojunction photovoltaic devices.