Interfacial Energy-Level Positioning in Stacked Phthalocyanine Heterostructures for Potential Use in Organic Solar Cell Applications: From Optical Response to Ambient-Induced Surface Effects

This study presents the comprehensive characterization of a phthalocyanine-based energy cascade for potential use in organic solar cell (OSC) application. By integrating four carefully selected materials, the proposed structure combines broad optical absorption with a cascade-like energy-level arrangement. Optical analysis and density functional theory calculations show broad spectral coverage arising from the combined contributions of the individual phthalocyanine layers. In parallel, X-ray photoelectron and ultraviolet photoelectron spectroscopies establish a well-defined frontier-orbital alignment and a uniform surface potential in the as-prepared stacked structure. Complementary calculations and photoemission measurements further demonstrate that controlled exposure of the terminal H2Pc layer to common atmospheric species induces slight modifications of the surface potential and energy-level alignment. These changes alter the electronic conditions at the H2Pc/TiOPc interface without detectable chemical degradation of the exposed layer, showing that ambient exposure can modify the interfacial energetics of the multilayer. Together, these results provide a detailed picture of the relationship between optical response, electronic structure, and ambientinduced interfacial modification in the investigated system and establish a basis for further device-level studies required to determine how these effects influence charge transport and photovoltaic performance.