Study On Highly Efficient Perovskite Solar Cells

Organic-inorganic perovskite solar cells have been favored by many researchers due to their advantages of excellent photoelectric properties,simple manufacturing process and excellent photoelectric conversion efficiency,and became the hot research of clean and renewable energy in recent years.Perovskite solar cells are mainly composed of FTO layer,electron transfer layer,perovskite absorption layer,hole transfer layer and metal electrode layer,wherein the light absorption layer is the core component of perovskite solar cells.The quality of perovskite film was crucial for achieving high efficiency perovskite solar.During the traditional one-step solution deposition of perovskite films,there would arise many problems,such as disordered crystal growth,poor film crystallinity and poor morphology quality,which limited the photoelectric performance of the device.Therefore,optimizing the film preparation process and improving the quality of perovskite films was very important to obtain high efficiency perovskite solar cells.Based on the improvement of the photoelectric properties of perovskite solar cells,the research on the improving the preparation process of the perovskite films were developed in this paper.The main research work was as follows:1.High-quality CH3NH3PbI3 perovskite films were prepared by adding 4-tert-butylpyridine(tBP)and pyridine(PY)additives were introduced into the antisolvent during one-step solution deposition process.tBP and PY as an electron-pair donating Lewis base with nitrogen donor,could form Lewis adducts tBP·PbI2 DMSO and PY·PbI2 DMSO with Lewis acid PbI2 in CH3NH3PbI3 precursor solution.The intermediate phases could suppress the nucleation number and growth of CH3NH3PbI3 perovskite films,resulting in formation of uniform CH3NH3PbI3 film with large grain size.The photoelectric conversion efficiency of the perovskite device has achieved 18.92%.In addition,the addition of tBP and PY in the antisolvent could induce the additives in the perovskite to form a gradient structure,which made more additives on the surface of perovskite film.Because of the gradient structure of additive distribution in CH3NH3PbI3,the tBP and PY additives concentrations in the perovskite were much less than tBP on the surface of the perovskite,the presence of tBP and PY additives on the surface of perovskite could effectively improve the moisture resistance of perovskite films and enhance the stability of perovskite devices.2.Due to the band gap of CH(NH2)2PbI3(FAPbI3)was about 1.48 eV,which was close to the optimal value of single junction solar cells.However,the black phase FAPbI3 was easily converted into yellow phase FAPbI3 during the one step solution deposition process.Therefore,the sequential dropping of chlorobenzene(CB)and methylammonium chloride(MACl)in isopropanol method was used to control the perovskite nucleation growth process to obtain the high-quality and smooth FA based perovskite film.By comparing the different deposition sequence of MACl and CB,it was found that early introduction of MACl additive could easily lead to form uncontrollable nucleation on the substrate.After annealing,these nuclei tended to form different sizes of perovskite particles with randomly arranged seeds in various orientations and heights,which was easy to cause a large number of disordered grain boundaries on the TiO2 layer.However,when MACl additive was introduced in last step,the nucleation seeds of the intermediate phase with uniform preferred orientation and distribution was formed on the substrate.After annealing,a compact FAPbI3 film with larger crystal grains and less grain boundaries and defects was obtained on the TiO2 layer.Therefore,the photoelectric conversion efficiency of the best perovskite device reached 20.08%.At the same time,high quality perovskite films also significantly improved the stability of the perovskite device.3.Due to the surface defect state of perovskite,it provided a corrosion channel for humidity and temperature.The post-treatment method was adopted to fabricate a thin 2D ethylenediamine lead iodide(EDAPbI4)layer on the top of 3D FAPbI3 layer for efficient and stable 2D-3D-based devices.On the one hand,the 2D-3D perovskite film could effectively suppress the charge recombination in 2D-3D based device,thus achieving higher photoelectric conversion efficiency.On the other hand,benefiting from the high moisture resistance of the 2D film,the 2D-3D based device demonstrated remarkably enhanced long-term stability.4.In addition,we synthesized the NaYF4:Yb3+,Er3+materials and doped in the TiO2 mesoporous layer to formed the TiO2/NaYF4:Yb3+,Er3+heterojunction materials after annealing.On the one hand,the TiO2/NaYF4:Yb3+,Er3+mesoporous layer absorbed the near infrared light at 980 nm,the electrons at 660 nm(4F9/2-4I15/2)excited state level were quenched via a radiative path.At the same time,the converted red light could be absorbed by the perovskite absorption layer,which could effectively broaden the spectral response range of the perovskite solar cells.On the other hand,the TiO2/NaYF4:Yb3+,Er3+mesoporous layer absorbed the infrared light at 980 nm,and the electrons in the 520 nm(2H11/2-4I15/2)?545 nm(4S3/2-4I15/2)excited state level could directly inject into the conduction band layer of TiO2 by the shared interfaces between TiI2 and NaYF4:Yb3+,Er3+.At last,the short-circuit current of perovskite device was significantly increased,and the photoelectric conversion efficiency of devices was also increased from 17.36 to 18.62%.