Simultaneous engineering of the conductivity and work function of biphenylene via fluorine adsorption

Biphenylene (BP) is a new member of the two-dimensional C nanomaterial family, and successful fabrication of BP offers an excellent opportunity for developing innovative C-based electronics. However, its unusual metallicity critically restricts its applications in field-effect transistors (FETs) and photocatalysis. Simultaneously, its relatively low work function (ϕ, 4.33 eV) seriously restricts its applications in anode materials of electronic devices. Therefore, understanding the tunabilities of electronic properties and ϕ of BP-based nanomaterials is crucial to guide experimental exploration; nevertheless, to date, little attention has been paid to this area. Herein, we theoretically demonstrate that conductivity of fluorinated BP (F_n-BP) evolves in the order metallic → semimetallic → semiconductivity with increasing F concentration, attributed to a bonding transition of BP (sp² → sp² + sp³ → sp³). Particularly, ϕ of BP can be significantly improved (4.82–6.97 eV) by fluorination, approximately two-fold higher than that of F_n-graphene owing to p electron transfer between F and BP. Consequently, metallic F_2D-BP and semimetallic F_4S-BP with favorable ϕs can be utilized as substitutes for Au and Pt anodes, respectively. Specifically, F_8D-BP, F_16D-BP, and F_24D-BP with exceptional band gaps of 0.40, 2.80, and 3.44 eV, respectively, exhibit high potentials for making channel materials in FETs, candidate materials in photocatalysis, and buffer layers in solar cells, respectively.