(a) Sketch of one-layer black phosphorus's (phosphorene) crystal structure, showing Li atom's (green atom) most stable adsorption site. Orange atoms represent the four atoms of the black phosphorus's primitive cell. (b) The Brillouin zone of black phosphorus. The ARPES spectra (referred to the chemical potential) of pristine black phosphorus recorded for (c) ZU and (d) ZT symmetry directions. ARPES spectra after Li doping along the (e) ZU and (f) ZT symmetry directions. (g) and (h) Depict the XPS spectra of the P2p and the Li1s core levels of doped black phosphorus, respectively. In panel (i), we report the x-ray absorption spectra for pristine and doped black phosphorus.