Unveiling the Interfacial Charge Dynamics in Organic Heterostructures: From Density Functional Theory Calculations to Application in Ambipolar Sensors

Understanding interfacial charge transport in organic heterostructures is important to enhance the related electronic device performances. However, the atomistic/molecular-scale insights into the interfacial charge accumulation and transport are currently missing, hindering the precise design of organic heterostructures for targeted applications. In this endeavor, the present work reports a correlated experimental electrical study and first-principles calculations to unravel the interfacial charge accumulation and transfer in metal phthalocyanines (MPc)-based bilayer organic heterostructures. The tuning of interfacial charge dynamics in Cu(F x Pc)/LuPc 2 heterostructures by fluorination is investigated, and its implication on the device semiconducting nature through NH 3 sensing is finally assessed. Structural optimization by density functional theory (DFT) reveals a distortion in the interfacial structure with increasing fluorination in Cu(F x Pc), which indeed enhances the binding of the macrocycles and accumulation of mobile charges. Electrical impedance measurements further reinforce this prediction, unveiling higher interfacial heterogeneity and charge accumulation in fluorinated CuPc-based heterostructures. Under exposure to a reducing gas NH 3, the heterostructures exhibit p-type, ambipolar, and n-type charge transport properties, for degrees of fluorination in the Cu(F x Pc) component x = 0, 8, and 16, respectively. Such transition in the semiconducting properties is finally correlated to interfacial intermolecular and intramolecular charge transfer analysis by DFT, confirming a net electron accumulation and depletion in the device conduction channel at the interface for fluorination degrees of x = 16 and 0, respectively.