Electron doping in FeSe monolayer and multilayer via metal phthalocyanine adsorption: A first-principles investigation

Electron doping has been established as an effective method to enhance the superconducting transition temperature and superconducting energy gap of FeSe thin films on strontium titanate (SrTiO₃) substrates. Previous studies have demonstrated that electron/hole doping can be achieved through the adsorption of metal phthalocyanine (MPc, M = Co, Cu, Mn, Fe, and Ni) molecules on surfaces. This work explores the electron doping induced by the adsorption of MPc molecules, specifically cobalt phthalocyanine (CoPc) and copper phthalocyanine (CuPc), onto FeSe monolayer and multilayers. Utilizing first-principles calculations based on density functional theory, we demonstrate that charge rearrangement occurs when MPc molecules adsorb on the FeSe substrate, contributing to an accumulation of electrons at the interface. In the CoPc/FeSe systems, the electron accumulation increases with the layer number of FeSe substrate, converging for substrates with 3–5 layers. The analysis of the integrated planar charge difference up to the position with zero integrated charge transfer reveals that all the five MPc molecules donate electrons to the uppermost FeSe layer. The electron donation suggests that MPc adsorption can be a promising strategy to modulate the superconductivity of FeSe layers.