Axially phenoxylated aluminum phthalocyanines and their application in organic photovoltaic cells

Abstract

Novel axially phenoxylated aluminium phthalocyanines, pentafluorophenoxy aluminium phthalocyanine (F₅PhO-AlPc) and p-nitrophenoxy aluminium phthalocyanine (NO₂PhO-AlPc), were synthesized through a one-step reaction starting from the commonly used photoactive material, chloro aluminium phthalocyanine (Cl-AlPc), and the respective phenols. Reactions with other phenols did not yield corresponding AlPc derivatives. Optical, electrical, and thermal analyses were carried out on F₅PhO-AlPc and NO₂PhO-AlPc using UV-Vis measurements (solution and thin-film), cyclic voltammetry (CV), differential-pulse voltammetry (DPV), and thermogravimetric analysis (TGA). A simple thermodynamic model was used to explain the lack of reaction when Cl-AlPc was treated a variety of alkylated phenols. We noted a side reaction producing fluoro aluminium phthalocyanine (F-AlPc) when the synthesis of F₅PhO-AlPc was attempted in DMF. The model also explains this observation. F₅PhO-AlPc and NO₂PhO-AlPc were integrated into organic photovoltaic devices (OPVs) both as electron-donating and as electron-accepting materials. The phenoxy-AlPcs enable an enhancement of the open-circuit voltage (V_OC) of the OPVs when applied as either an electron donor or as an electron acceptor compared to Cl-AlPc. The results within the OPV, specifically the increased V_OC, are consistent with the steric shielding effect seen in other OPVs.