6533b7d8fe1ef96bd126b7cb

RESEARCH PRODUCT

Photon assisted-inversion of majority charge carriers in molecular semiconductor-based organic heterojunctions

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International audience; Ambipolar molecular materials hold great promises as a building block of next generation highly efficient, less complex and low cost electronics devices. In this endeavor, the present work reports the fabrication of organic heterojunction devices based on halogenated copper Phthalocyanines (CuPc) and lutetium bisphthalocyanine (LuPc2) bilayer, investigates their structural and electrical properties and probes the ambipolar behavior by ammonia sensing. Microstructural analysis of the heterostructure thin films revealed compact and semicrystalline organization, depending on the number of halogen substituents in CuPc. The heterojunction devices reveal a non-linear I(V) characteristics associated with interfacial energy barrier which is tuned by the number and type of halogen substituents. The devices behavior towards NH3 exposure revealed n-type, p-type and ambipolar transport depending on 16, 0 and 8 fluorine substituents, respectively present in CuPc component of the heterostructure, demonstrating a correlation between electronic effects of substituents to the thin film electrical properties. The trigger of ambipolar transport regime in the heterojunction device is the visible light, such that device conduction channel is dominated by holes in the dark and electrons under illumination. In depth charge transport studies by impedance spectroscopy explains the device electrical behavior and highlights the important role played by the interface in the heterostructures. Different charge transport parameters are extracted by fitting of the experimental Nyquist curves, analysis of those confirm the presence of bulk and interfacial transport and provides an interpretation of the observed ambipolarity.