| The efficient use of solar energy is an important way to reduce dependence on petrochemical energy and realize green and low-carbon energy.Tin-based halogen perovskite cell is a kind of solar cell with high photoelectric conversion efficiency and promising commercial application.To further improve its photoelectric stability is the key to promote the commercial use of tin-based halogen perovskite cell.The photoelectric stability and conversion efficiency of solar cell materials are closely related to the electronic structure and the properties of electronic transmission interface.The electronic structure,differential charge distribution and optical properties of Bγ-Cs Sn I3 doped F,Cs2Sn I6 doped F and Bγ-Cs Sn I3 doped Mn absorption layer materials were studied by first-principles method.And the electron buffer layer interface to assist the absorption layer to carry out electron transport,and the electron transport mechanism of Zn O/graphene composite electronic transport interface.Combined with experiments and literature,the main conclusions are as follows:1.The mixing ratio of F can adjust the band gap width of Bγ-Cs Sn I3-xFx structure.With the increasing of the mixing ratio of F,the formation energy of Bγ-Cs Sn I3-xFxgradually decreases and the band gap gradually increases,and the binding ability of the highly electronegative F atom to Sn atom improves,and an obvious covalent bond is formed between F and Sn,resulting in stable F-Sn-I group.As a result,the transformation from Sn2+to Sn4+becomes more difficult,which effectively delays the transformation process from Bγ-Cs Sn I3-xFx to Cs2Sn I6,and improves the stability of the Bγ-Cs Sn I3-xFxstructure.2.In the Cs2Sn I6-xFx structure of double-layer perovskite,F replaces some nodes of I and changes the internal local structure of the crystal,resulting in the diffraction peak of（22 2）crystal plane weakened and（0 0 4）crystal plane enhanced.At the same time,the band gap of the material increases significantly,and the high-density pear-shaped electron cloud around the F atom,Cs2Sn I6-xFx structure has infrared transmittance,strong absorption peak and energy loss peak appear in the short-wave ULTRAVIOLET region,and has ultraviolet luminescence.3.The Bγ-Cs Sn1-xMnxI3 structure is formed by replacing Sn atoms with Mn atoms in proportion.With the increase of Mn doping ratio,the stability of the Bγ-Cs Sn1-xMnxI3decreases and the formation energy increases,which is consistent with the larger grain size formed at high doping ratio.The calculation results of spin electron state density of Mn transition elements show that the quantum states with spin up and spin down are asymmetrical and ferromagnetic,and the magnetic moment decreases with the increase of Mn doping ratio.The spectral results show that the blue shift is caused by Mn doping,and two strong absorption peaks appear in the uv region,which verifies that the Bγ-Cs Sn1-xMnxI3 has luminescence characteristics in the UV region.The higher the proportion of Mn,the higher the light absorption intensity,the greater the energy loss,the higher the luminous efficiency.4.The work functions of Bγ-Cs Sn I3-xFx,Cs2Sn I6-xFx and Bγ-Cs Sn1-xMnxI3 materials are different with different doping elements and ratios.Based on the results of work function,the energy level structures of three kinds of perovskite light-absorbing materials were established.By comparing with the energy level structures of Zn O/Sn O2/Ti O2,the electronic transition potential barriers between the light-absorbing materials and the buffer layer in different combinations were obtained.The lowest electron injection barrier between Bγ-Cs Sn I2.625F0.375 and Sn O2 is 0.284e V.The lowest electron transition barrier between Cs2Sn I5F1 and Zn O is 0.062e V,which is easy for electron transport.Mn doped Bγ-Cs Sn1-xMnxI3 materials are prone to vacancy binding,which inhibits electron transport.5.The electron transport composite formed by graphene and Zn O with excellent electrical conductivity should have excellent electrical properties,but the experimental results show that the electrical properties of Zn O/graphene composite prepared by evaporation are not ideal,and it is found that the evaporation Zn O on the graphene substrate is amorphous Zn O thin film.First-principles calculations show that carbon-oxygen covalent bond is formed between the amorphous Zn O/graphene interface,which has strong binding effect on electrons,resulting in abnormal electrical properties,and the amorphous Zn O structure is not conducive to electron transport at the Zn O/graphene interface. |
