Supplementary Information

See the supplementary materials for detailed formulas, figures related to data; The effective masses of heterostructures CSUP and CSDN; Band structures of free-standing Sc2CO2, Cs2PbI2Cl2; Electrostatic potentials of free-standing Sc2CO2, Cs2PbI2Cl2 and heterostructures; Lattice mismatch, charge-density isosurfaces, lattice deformation functions along a-axis and b-axis, projected band structures under different electric fields and stresses, device models, current-voltage characteristic and on/off ratio of CSUP and CSDN.