Decoding Fluorine Peripheral Substitution Impact in Zinc Phthalocyanines for Perovskite Solar Cells

Abstract

We designed six zinc phthalocyanine derivatives (ZnPc-1-ZnPc-6) as molecular semiconductors. By adjusting peripheral substituents with differing electron-donating and -withdrawing properties (-C(CH3)3, -O(CH2)CF3, -CF3), we rationalized solubility, energy levels, and molecular arrangement to influence interfacial charge dynamics and thus device performance. Among the derivatives, ZnPc-2 with three tert-butyl groups and a trifluoroethoxy provides favorable energy level alignment, better thin film coverage, and high conductivity suited to be used as hole-selective materials. When integrated into n-i-p architecture perovskite solar cells, it measures a power conversion efficiency approaches that of Spiro-OMeTAD under our lab conditions. ZnPc-2 showed ambient operational stability, maintaining around 80% of its initial JMPP over 24 h without encapsulation. Our combined theoretical and experimental assessment revealed detailed electro-optical properties to substantiate the influence of molecule design on the device performance. Specifically, three tert-butyl groups with a trifluoroethoxy arm outperform, evidencing molecular design as a strategy to modulate properties.