Oxy phosphorus tetrabenzotriazacorrole: firming up the chemical structure and identifying organic photovoltaic functionality to leverage its unique dual absorbance

Abstract

The structure of oxy phosphorus tetrabenzotriazacorrole (POTbc) was firmed up using time-of-flight electron ionization mass spectrometry (TOF-EI MS), elemental analysis (EA), and core level X-ray photoelectron spectroscopy (XPS), addressing the contradictions in the literature around the nature of the bond between the phosphorus atom center and the axial oxygen atom(s). Pre-device fabrication physical characterization of POTbc was conducted in the solid-state using ultraviolet photoelectron spectroscopy (UPS), optical measurements, and thermogravimetric analysis (TGA) to enable appropriate device integration. POTbc, tetrabenzotriazacorroles in general, was then applied for the first time in an organic electronic device, a planar heterojunction organic photovoltaic (PHJ OPV). The functionality of POTbc was confirmed in PHJ OPV devices by pairing with conventional organic semiconductors, with fullerenes, C₆₀ and C₇₀, as an electron donor and with α-sexithiophene as an electron acceptor. POTbc showed highest promise as an electron donor within a POTbc:C₇₀ based OPV owing to external quantum efficiencies broadly across the entire visible spectrum (300 nm–750 nm). The thicknesses of the POTbc and C₇₀ active layers was then probed and a PHJ OPV with 1.96% power conversion efficiency (PCE) was achieved. The high short-circuit current densities (J_SC) obtained with the POTbc:fullerene based OPVs is attributable to the unusual dual absorbance of POTbc in the visible spectrum, yielding a conclusion that POTbc and other Tbc derivatives are promising functional organic electronic materials for visible light harvesting applications.