High Stable Perovskite Solar Cells Prepared By Vacuum Evaporation

As a typical third-generation solar cells,the power conversion efficiency?PCE?of perovskite solar cells?PSCs?is comparable to monocrystalline silicon solar cells.Obviously,PSCs are expected to have a place in the future solar energy field.Although the PCE of PSCs in laboratory has been hitting new highs,the problem of stability has not been well solved.Besides,there is no suitable preparation process for large-area PSCs.Long-term stability is a necessary requirement for solar cells applications,and the preparation of large-area PSCs is the only way to industrialization.Therefore,it is vital to develop a suitable preparation process for large-area and high stable PSCs.Films prepared by vapor processing methods such as vacuum evaporation and chemical vapor deposition?CVD?are uniform and continuous,which are suitable for large-area PSCs devices.In this paper,vacuum evaporation and CVD techniques are used to prepare high stability PSCs.By optimizing the fabrication process,high quality films and optimum device performance were obtained.The long-term stability of the devices was also tested.The main contents of this paper are listed as following:1.We used CuPc as hole transport layer?HTL?to prepare inverted organic-inorganic hybrid PSCs by fully vapor deposition.By optimizing the thickness of HTL,the PCE of the device achieved 12.06%.With encapsulation,the device maintained 73%of initial PCE after keeping at 85?for 30 days.The high PCE and excellent stability should be attribute to the good physical and chemical stability of CuPc.2.In order to further improve the thermal stability of perovskite,we prepared CsPbBr₃ perovskite films by immersing vapor-deposited PbBr₂ in a solution of CsBr.The high-purity CsPbBr₃ perovskite film was obtained by using a multiple immersion method to control the progress of the reaction.Using the films,we prepared all-inorganic PSCs with a structure of FTO/c-TiO₂/CsPbBr₃/Carbon,and a PCE of4.61%was achieved.In addition,the device with encapsulation maintained 83%of initial PCE after keeping at 85?for 30 days.3.We developed a multiple sequential vapor deposition?MSVD?method to prepare high quality CsPbBr₃ films.CsBr and PbBr₂ were deposited on the substrate layer by layer.A solid phase reaction is performed to form CsPbBr₃ films after annealing.By adjusting the annealing temperature and humidity,we improved the morphology and crystallization of the film.Finally,the HTL-free CsPbBr₃ PSCs achieved a PCE of 7.13%.4.On the basis of MSVD,we added a small amount of excess PbBr₂ to prepare CsPbBr₃-CsPb₂Br₅ composite films.We found that the faster heating rate during annealing,the larger grain size we obtained.The optimized CsPbBr₃-CsPb₂Br₅ film have a grain size of 4?m,and the corresponding PSCs have achieved a PCE of8.86%.To the best of our knowledge,this is the highest PCE of planar CsPbBr₃ PSCs that have been reported so far.In order to remove the non-perovskite phase in the CsPbBr₃-CsPb₂Br₅ composite film,we placed the composite film in the vapor of methyl bromide?FABr?to obtain Cs_1-xFA_xPbBr₃ perovskite film.The Cs_1-x-x FA_xPbBr₃film has a larger grain size,and the device prepared by the film not only exhibits superior PCE,but also has better stability.With encapsulation,the device maintained90%of initial PCE after keeping at 85?for 30 days.