Studies On The Stability Of Two-dimensional And Three-dimensional Mixed Tin-based Perovskite Solar Cells

In recent years,solar cells using organic-inorganic hybrid lead perovskite as light absorbing materials have become a new research hotspot in the field of photovoltaic technology.At present,the power conversion efficiency of hybrid lead halide perovskite solar cells（PSCs）has exceeded 25%,which is comparable to that of crystalline silicon solar cells.However,these solar cells contain lead,the potential harm of which is bound to become a challenge in their future application.Tin belongs to the same main group with lead.It shows similar physical and chemical properties while it is non-toxic.More importantly,tin-based perovskite shows the wider light absorption range and high carrier mobility,making it one of the most promising highly efficient green energy materials.At present,the main problem of tin-based perovskite solar cells is that Sn²⁺can be easily oxidized to Sn⁴⁺,leading to a poor stability and low efficiency for corresponding photovoltaic devices.To solve the above problem,our study follows international research frontier and trys to improve the stability of tin-based perovskite applying two-dimensional（2D）and three-dimensional（3D）mixed structures.We intensively studied the important roles of different organic cations on the crystal quality and stability of tin-base perovskite films,and revealed that organic cations have a great effect on regusting the dimension,the phase distribution and the crystal growth orientation.The results reveal that the organic cations play an important role on the charge transport path.This study provides valueable guide for designing efficient and stable tin-base perovskite solar cells.The main research contents of this paper are as follows:Since two-dimensional ruddlesden-popper（RP）lead-based perovskite has showed high stability and good photovoltaic performance,tin was first introduced into the 2D RP lead-based perovskite to replace lead and Pb-Sn mixed perovskite light absorbing materials were therefore obtained.2D and 3D Pb-Sn mixed perovskite films were prepared by introducing organic spacer cations into perovskite precursor solution.The light absorption property and surface morphology of RP Pb-Sn mixed perovskite films at different n values reveals the phase separation problem in Pb-Sn films.By further optimizing the preparation parameters of thin films and completely replacing lead with tin,we effectively overcame the problem of phase separation.And the low-dimensional tin-based perovskite solar cells obtained an efficiency of more than 4%.The size and structure of organic spacer cations have an important influence on the properties of RP perovskite films.We then introduced different alkyl chain length cations（butylamine,octylamine and dodecylamine cations）to the perovskite precursor,and prepared different alkyl chain length of tin-base perovskite thin films.It proves that different alkyl chain length in the tin-base perovskite has a significant effect on films’crystal quality,crystal orientation and dimension distribution.The experimental results of grazing incident wide-angle X-ray scattering and photoemission spectrum show that the organic cation with shorter chain length is more conducive to the vertical orientation growth and orderly phase distribution of the crystal.These characteristics enhance the charge transport properties in the low-dimensional tin-based films and effectively inhibit the oxidation of Sn²⁺to Sn⁴⁺.