Organic-inorganic lead based halide perovskites were experimentally observed with enhanced solar cell performance and larger open-circuit voltage after the treatment of the crystal surfaces with pyridine.We model the Pb-I2 terminated perovskite surfaces and find pyridine and ethylamine,will interact with the surfaces and tune their electronic band gap.Due to the most stable perovskite system with consistently orientated methylammounium(MA)molecules,the doped surfaces whose dopants has the parallel polarity as MA pointed to the interface will differentiate with the doped ones with antiparallel polarity.Here,based on density-functional theory(DFT)calculations,we demonstrate that the ethylamine and pyridine with inverted polarities,compared with the previous MA cations in systems,can enlarge the band gaps of perovskite surfaces.We ascribed the change of electronic properties to the cancellation of the dipole moments caused by the pyridine and methylamnion molecules on surfaces.Furthermore,we vary the polarities of MA cations by interchanging the C and N atoms in a symmetric fashion for showing the influence of polarization on total energies,electronic properties and charge distributions.