Integrated Transport Analysis and Dynamic Photoexcitation of Interfacial Electronic States in Copper Phthalocyanine Nanojunctions

Organic semiconductors (OSCs), particularly copper phthalocyanine (CuPc), are critical to next-generation flexible electronics. While CuPc-based devices show great promise, complex charge transport mechanisms and optoelectronic dynamics fundamentally limit their performance and reliability at the molecular interface. This work presents an integrated, multimodal tunneling spectroscopy study to dissect these critical nanoscale processes. Specifically, by investigating the CuPc/highly oriented pyrolytic graphite (HOPG) interface, we established the electronic foundation, confirming Schottky barrier alignment and identifying a shallow-trap depth of 38 meV using classical transport models. Analysis of I-V characteristics across varying temperature and electric field regimes revealed that charge transport is governed by the coexistence of Richardson-Schottky emission, Poole-Frenkel conduction, and Fowler-Nordheim tunneling, with the low apparent barrier height (Φapp ≈ 0.1 eV) indicating significant interfacial inhomogeneity. Crucially, inelastic electron tunneling spectroscopy (IETS) identifies specific molecular vibrations, confirming that vibronic coupling provides an essential inelastic pathway for carriers. Finally, the dynamic optoelectronic response was investigated. Under UV illumination, a significant modification of the local density of states (LDOS) is observed, characterized by a pronounced Gaussian distribution of photopopulated interfacial states. Density functional theory (DFT) and vibrational analysis were conducted to correlate the observed electronic states and molecular vibrations with the experimental spectroscopic data. This integrated understanding of electron-vibration interactions and light-induced interfacial dynamics provides a mechanistic foundation for controlling charge injection and optimizing the functional response of molecular-scale electronic architectures.