Strain tuning of optoelectronic properties of covalent organic framework bilayers and heterostructures

Heterostructures composed of two-dimensional materials have gained significant attention due to their unique properties and potential applications in various fields. Covalent organic frameworks (COFs) represent a novel class of organic porous materials that have shown promise in gas storage, catalysis, and optoelectronics. In this paper, we present a first-principles study of the optoelectronic properties of bilayers and heterostructures of C6N6 and B6O6 COFs, including excitonic effects within the G0W0-BSE approach and the effects of van der Waals corrections. Our study shows that the energetically favorable configuration is AC-stacking, where the upper pore is covered by the C-N (B-O) ring of the bottom layer. We also found that the AC-stacking C6N6/B6O6 heterostructure exhibits a surface buckling of 0.55 angstrom and an intrinsic type II band alignment, resulting in a redshift in optical absorption. The calculated band edge alignments for C6N6 and B6O6 monolayers and heterostructures using the HSE06 hybrid functional affirm their suitability for the photocatalytic splitting of water. Furthermore, we investigated the impact of strain on the band gap and demonstrated that increasing tensile strain leads to a decrease in the distance between the two layers, causing an increase in the electronic band gap and optical gap. These results provide a solid theoretical foundation for future experimental investigations and suggest potential applications in optoelectronic devices. Overall, our study sheds light on the optoelectronic properties of COF heterostructures and highlights their potential for use in a range of important applications.