Influence of Stacking Order of Phthalocyanine and Fullerene Layers on the Photoexcited Carrier Dynamics in Model Organic Solar Cell

Abstract

Metal phthalocyanine and fullerene are typical p-type and n-type organic semiconductors and are often used as constituents of model systems of organic photovoltaics (OPVs). The light–electricity conversion efficiency of the OPVs is influenced by many factors, and a composite structure is one of them. In the present study, time-resolved X-ray photoelectron spectroscopy has been utilized to examine the influence of the stacking order of copper phthalocyanine (CuPc) and fullerene (C60) on photoexcited carrier dynamics in layered CuPc–C60 thin-film OPVs fabricated on a rutile TiO2(110) substrate. TiO2 is a strong n-type semiconductor and is found to serve as an electron acceptor, which collects the excited electrons in both CuPc and C60 layers irrespective of their stacking order. However, a clear difference is found in the electron transfer from C60 to TiO2 in short delay times below 1 ns; an electron transfer is facilitated in CuPc/C60/TiO2 stacking, whereas the fast electron transfer is suppressed in C60/CuPc/TiO2 stacking. The insertion of the CuPc layer between C60 and TiO2 is effective to block the C60 → TiO2 electron transfer even though the CuPc layer has a monolayer thickness.

Modulation of charge transfer exciton dynamics in organic semiconductors using different structural arrangements

“…6,7 In recent years, many studies pointed out the active role of the aggregation and intermolecular interactions in tuning the photo-physical and dynamical carrier properties of the film, affecting the light absorption, the energy level alignment, the exciton diffusion, allowing for more efficient charge transport in the material. [6][7][8][9][10][11] As a consequence, accurate control of the molecular structure in the solid aggregation is a key factor in designing and optimizing the device performance, implying the possibility of ad hoc engineering of the electronic properties and the carrier transport dynamics in molecular films. Here we demonstrate how different molecular structural arrangements modulate the CT exciton dynamic in ordered cobalt phthalocyanine (CoPc) thin films.…”