Tunable mechanical and optoelectronic behavior of BC <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si6.svg" display="inline" id="d1e1081"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> N m

Two-dimensional boron–carbon–nitrogen (BCN) materials represent a versatile class of layered compounds that bridge the electronic and structural characteristics of graphene and hexagonal boron nitride. Among these, the BC 2 N stoichiometry offers highly tunable properties but remains unexplored. We report a first-principles investigation of monolayer BC 2 N, exploring eleven possible atomic configurations. Phonon and ab initio molecular dynamics simulations reveal six dynamically and thermally stable structures. The stable monolayers display high in-plane stiffness with elastic constants of 252–305 N/m and Young’s moduli between 743 and 844 GPa, achieving ultimate strengths up to 104 GPa. Electronic band structures calculated with the HSE06 functional show that, while one configuration exhibits metallic behavior, the others possess direct band gaps ranging from 0.29 to 2.71 eV. Furthermore, exciton binding energies obtained via the Bethe–Salpeter equation vary from 134 to 471 meV. The spectroscopic limited maximum efficiency (SLME) analysis reveals promising photovoltaic performance, with specific structural phases achieving efficiencies of 20.5% and 31.5%. These findings demonstrate the tunable mechanical, electronic, and optical properties of BC 2 N monolayers and their potential for next-generation optoelectronic and solar energy harvesting devices.