IMPACT OF SOLVENT VAPOR ANNEALING ON THE MORPHOLOGY AND PHOTOPHYSICS OF MOLECULAR SEMICONDUCTOR THIN-FILMS

The effect of solvent vapor annealing on the fluorescence properties a nd morphology of titanyl phthalocyanine/ perylene phenethylimide thin- film molecular semiconductor bilayers (TiOPc/PPEI) is investigated. A combination of atomic force microscopy (AFM) and near-field scanning o ptical microscopy (NSOM) is used in conjunction with bulk absorption a nd fluorescence measurements to correlate the morphological and photop hysical properties of these bilayer systems. AFM data show that treatm ent of the vacuum-deposited amorphous PPEI and TiOPc/PPEI films result s in the crystalline transformation of these materials and severely al ters the contact between the TiOPc and PPEI layers. AFM data show exte nded solvent vapor annealing produces void spaces in the TiOPc coverag e on the order of several hundred nanometers. Steady-state fluorescenc e intensity and fluorescence lifetime measurements are used as a measu re of charge-transfer quenching efficiencies. Very efficient charge-tr ansfer quenching is observed when amorphous layers of TiOPc are deposi ted onto PPEI resulting from uniform contact between the layers. Exten ded annealing results in decreased charge-transfer quenching efficienc ies as a result of widely dispersed, localized interfacial contact poi nts.