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(FxPc)/LuPc2 heterostructures by fluorination is investigated, and its implication on the device semiconducting nature through NH3 sensing is finally assessed. Structural optimization by density functional theory (DFT) reveals a distortion in the interfacial structure with increasing fluorination in Cu(FxPc), 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 NH3, the heterostructures exhibit p-type, ambipolar, and n-type charge transport properties, for degrees of fluorination in the Cu(FxPc) 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.