Small-Molecule-Based Organic Photovoltaic Devices Covering Visible and Near-Infrared Absorption through Phase Transition of Titanylphthalocyanine Induced by Solvent Exposure

Abstract

Small-molecule p–n heterojunction organic photovoltaic (OPV) devices with a two-component donor layer composed of tetrabenzoporphyrin (BP) and titanyl phthalocyanine (TiOPc) can utilize near-infrared (NIR) light up to 950 nm and shows a 2.4% power conversion efficiency (PCE) (J _sc = 7.7 mA/cm²; open circuit voltage, V _oc = 0.61 V; and fill factor, FF= 0.50) under AM1.5G illumination at an intensity of 100 mW/cm². This value is higher than the 2.0% value obtained by an archetypal device composed of a single-component BP layer. The device performance was improved by the exposure of the TiOPc layer to toluene, which induced a rapid change in the morphology of the TiOPc layer from what is called Phase I to Phase II. The acceptor layer comprising 1,4-bis(dimethyl-phenylsilylmethyl)[60]fullerene (SIMEF) showed higher V _oc and PCE than that comprising popular PCBM, because the lowest unoccupied molecular orbital (LUMO) level of SIMEF is higher than that of PCBM.