CH ₃NH ₃PbI ₃is one of the most promising candidates for high-performance hybrid organic-inorganic perovskite solar cells. The CH ₃NH ₃PbI ₃single crystal and polycrystalline thin film exhibit the unique features of long carrier lifetimes and diffusion lengths, however, their carrier mobilities are in fact rather modest in a range from 1 cm ²·V ^–1·s ^–1to 100 cm ²·V ^–1·s ^–1. Experimentally, the temperature dependence of mobility is described as T ^–1.3to T ^–1.6due to the acoustic phonon scattering. To be sure, the rotating CH ₃NH ${}_3^+ $ cations are disadvantageous to the carrier transport and performance for CH ₃NH ₃PbI ₃solar cells. The effect of the rotating CH ₃NH ${}_3^+ $ cations on high-performance CH ₃NH ₃PbI ₃solar cells remains an open question. The Gaussian 09 software has been utilized to optimize the geometrical structures of CH ₃NH ₃dimer, trimer, tetramer, and pentamer in isolated state at the MP2 level with using the cc-PVTZ basis set. For CH ₃NH ₃polymer, the mean distance between two centroids of neighboring CH ₃NH ₃decreasing with the number of CH ₃NH ₃is slightly smaller than the lattice constant 6.28 Å of tetragonal CH ₃NH ₃PbI ₃, which is advantageous to structural stability and higher structural order of inorganic [PbI3] ^–framework. It signifies that the long range order of electrically neutral CH ₃NH ₃is easily formed for room-temperature CH ₃NH ₃PbI ₃. The total dipole moment linearly increases with the number of CH ₃NH ₃for CH ₃NH ₃polymer, and attains a large value 19.7 Debye for CH ₃NH ₃pentamer, which may be the origin of strong polarization in CH ₃NH ₃PbI ₃heterojunction. The molecular orbitals of five unpaired electrons for CH ₃NH ₃pentamer are distributed around NH ₃-sides of five different CH ₃NH ₃pentamers respectively, and these orbital energies are in a range from –4.4 eV to –3.2 eV. The unpaired electrons in CH ₃NH ₃polymer have an electrostatic attraction on the CH ₃-side of neighboring CH ₃NH ₃, which is the key cause of forming the ordered CH ₃NH ₃polymer. Hence it can be inferred that the orbital energies of unpaired electrons are getting closer when the longer range order of CH ₃NH ₃are formed in room-temperature CH ₃NH ₃PbI ₃through the interfacial electron injection. The vector field map of electrostatic potential (ESP) shows that CH ₃NH ${}_3^+ $ has strong electrophilic character, and the NH ₃-side has a stronger electrophilic character than CH ₃-side, however, CH ₃NH ₃monomer and polymer have weak electrophilic and nucleophilic character. Thus, the forming of CH ₃NH ₃polymer at the CH ₃NH ₃PbI ₃heterojunction leads the organic and inorganic portions to be decoupled, which can effectively reduce the anharmonic phonon modes. Under an applied electric field, the unpaired electrons in CH ₃NH ₃pentamer can transfer along the C-N axis through the hopping mechanism. According to these results, we can draw three useful conclusions below. i) The electrons under an applied electric field are easily injected into the CH ₃NH ₃PbI ₃material through the heterojunction, the CH ₃NH ₃polymer is easily formed, and the unpaired electrons in polymer are transferred between two neighboring CH ₃NH ₃through hopping mechanism. ii) The decoupling between organic CH ₃NH ₃and inorganic [PbI3] ^–framework can effectively reduce the anharmonic phonon modes, which can lead the carrier scattering decrease and the efficiency of carrier separation and transport to improve; iii) The ordered CH ₃NH ₃polymer at the CH ₃NH ₃PbI ₃heterojunction can enhance the order of inorganic [PbI3] ^–framework. Our researches may help to further understand the origin of high power conversion efficiency (PCE) for hybrid organic-inorganic perovskite solar cells.