1. Select monomers with HOMO-LUMO gaps of 3-4 eV. Conjugation will lower the HOMO-LUMO gap in the polymer, the stronger the conjugation, the stronger the reduction. In principle, molecular monomers that contain high concentrations of conjugated groups (such as phenyl, alkynyl and azaaryl) can be used as building units to construct 2D conjugated polymers. However, it is important to ensure that those conjugated groups can interact efficiently after polymerization, so that a high degree of conjugation of the constructed 2D polymers can be achieved.