Transport and photogalvanic properties of covalent functionalized monolayer black phosphorus

Abstract

Covalent functionalization is an efficient approach to modulate the nanoelectronic properties, advance the charge separation efficiency, and thus optimize the optoelectronic applications of nanomaterials. Here, the electronic structures, transport properties, and linear photogalvanic effects of two dimensional (2D) monolayer black phosphorus (MLBP) functionalized by PtCl₂ groups, (PtCl₂)_n-MLBP (n = 1, 2, and 4) have been theoretically investigated using density functional theory (DFT), nonequilibrium Green's function (NEGF), and the Keldysh nonequilibrium Green's functions (KNEGF) methods. In the functionalized systems, the valence band maximum comes from the PtCl₂ groups while the conduction band minimum originates from the MLBP. Such spatial charge separation hinders electron–hole recombination, suggesting MLBP-based 2D materials as promising candidates for solar cells. The MLBP-based device exhibits opposite responses for the transport properties and linear photogalvanic effects. The transport properties of MLBP along both the armchair and zigzag directions decrease after being grafted with PtCl₂ groups. Moreover, the larger the grafting density n, the lower the conductivity. In comparison, the linear photogalvanic effects augment after functionalization, and this phenomenon is more significant with large n. Further, the photoresponse in the zigzag direction is larger by an order of magnitude than that in the armchair direction.