Design And Preparation Of New Electronic Transport Layer In Perovskite Solar Cells

In recent years,the perovskite solar battery has become the most promising photovoltaic devices,due to its solution prepared ability.Compared with other types of solar cells,perovskite solar cell research has been widely concerned.Because perovskite solar cell preparation process is easy to operate,and equipment preparation cost less than traditional silicon solar cells,more than 20% of the efficiency has achived.The study of stability of equipment has some breakthrough.In perovskite type solar cell research,improve the planar solar cell efficiency through optimize the interface or the charge transfer ability have become important method.Hrer we will get down toreseach in the two aspects.1,For perovskite solar cells,organic lead iodide with formamidinium ions is a promising light harvester material with relative small energy band gap.And photovoltaic devices with planar junctions can be fabricated because of the long diffusion length of charge carriers.However,planar devices need perovskite layers with high quality.Pin hole defects and yellow ?-phase can lead to intensive recombination process,which is usually existed in the formamidinium perovskite layers by two step methods.In this study,[6,6]-phenyl-C61-butyric acid methyl ester?PCBM?is employed as the intermediate layers between Ti O₂ electron transport layers and formamidinium perovskite layers.SEM images indicate PCBM intermediate layers encourage the growth of grains in formamidinium perovskite layers.XRD patterns show PCBM layers eliminate the yellow ?-phase and improve the crystallization.By optimizing the concentration of PCBM precursor solutions,the average power conversion efficiency of formamidinium planar devices was promoted from 6.8 % to 15.1 %.And it is also noted that devices with optimized PCBM layers are free from hysteresis effect.Impedance spectra indicate this improvement comes from the suppression of recombination process by the PCBM intermediate layers.2,TiO₂ is a wildly used material of electron selective contact layers in perovskite solar cells.The function of Ti O₂/ MAPb I₃ interface can be modified by doping metal ions in the Ti O₂ layers.As lanthanide elements usually exhibit unique properties for their incompletely occupied 5d or 4f orbitals,the state with La3+ which can impress the recombination process of electron/hole.We prepared lanthanum doped Ti O₂ films by spray pyrolysis method as the electron selective contact of perovskite solar cells.SEM images indicate lanthanum dopants improve the smoothness of Ti O₂ layers.In the optimized concentration,the average PCE of devices is promoted from 12.4% to 14.4% with the highest PCE of 17.2%,which comes from the improvement on charge transfer and recombination.Moreover,the Lanthanum dopants also lead to the improvement of photo-stability for perovskite solar cells by impress MAPb I₃ decompose process.