Design of planar 2D semiconductors incorporating sp²-hybridized group 13 metals with boron, carbon, and nitrogen

The sp 2 -hybridization is key to understand structures of 2D materials with light p-block elements. However, hunting for sp 2 -hybridized 2D materials with heavy p-block elements remains challenging due to weaker π-bonding and increased steric effects. Here we proposed design principles for 2D materials based on carbon nitride with adjacent Lewis-acidic center of group IIIA elements. We introduce a family of 2D materials XB 9 C 4 N 6 (X = Al, Ga, In and Tl) with high thermodynamic stability. Density functional theory (DFT) calculations reveal that XB 9 C 4 N 6 exhibit a polycyclic lattice with high delocalized π electrons, primarily from B 6 ring, which play the key role in the hole and electron transports. These materials exhibit small electron effective mass of ~ 0.28m 0 , suitable bandgaps of ~ 1.2 eV and strong light absorption peaks of violet, red and near-infrared lights, which cover the solar spectral irradiance. Notably, AlB 9 C 4 N 6 emerges as an environmentally friendly semiconductor for electronics and photovoltaic devices. The design principles will enrich the fundamental understanding of π-conjugated heavy p-block elements and family of sp 2 -hybridized 2D materials. • A new designing principle is discovered in the π-conjugated III-A metals bonded B 6 ring and C 4 N 6 , planner XB 9 C 4 N 6 (X=Al,Ga,In,Tl). • Thermodynamically stable up to 1000k maintained by B 6 ring • Low entropy competed with typical 2D materials • Electron bandgap of about 1.2 eV and low effective electron mass (0.28-0.75 m 0 ) • Absorption spectra align with the solar radiation above 550 nm.