The Study On Alkali Metal Doped CH₃NH₃PbI₃ Thin Films And Solar Cells

Organic-inorganic hybrid perovskite solar cells have attracted much attention due to their high efficiency and simple preparation process.In order to improve the efficiency and stability of solar cells,the preparation of high quality perovskite films is particularly important.The CH₃NH₃PbI₃?MAPbI₃?is popular for its excellent optoelectronic properties such as suitable optical bandgap,small exciton binding energy and long diffusion distance.However,the environmental stability and thermal stability of MAPbI₃ are not good.Recently studies shown that cesium doping or adding alkali metal salts can increase crystallization and improve film quality.Therefore,based on the preparation of large grain MAPbI₃ thin films and the improvement of the stability of solar cells,the following studies are carried out in this paper:?1?Alkali metal iodide?NaI/KI/CsI?was added to the precursor of MAPbI₃.Perovskite precursor was prepared by non-stoichiometric method.The effects of alkali metal iodide doping on the MAPbI₃ thin films and solar cells were studied.Because of experiments in the air environment,the effect of humidity on the preparation of Perovskite Thin films was studied.When the humidity is lower than 20%RH,the Perovskite films with no pinholes and smooth surface can be prepared.Secondly,the effects of CsI doping MAPbI₃ thin films and solar cells were studied.When CsI doping content is 2%,the crystallinity,grain size and thermal stability of the films are improved significantly.The solar cell efficiency increased from 10.9%to 14.2%.the efficiency retained 13.9%after 5 weeks without encapsulation.Finally,the effects of different NaI/KI additions on the photoluminescence intensity of MAPbI₃ thin films were studied.It was found that when NaI/KI additions were 5%,the grain size increased significantly,and the internal defects decreased,which enhanced the photoluminescence intensity of the films.In addition,both of them could promote the growth of MAPbI₃ thin films along?310?surface.?2?The effects of post-treatment of alkali metal iodide?NaI/KI/CsI?solution on MAPbI₃ thin films and solar cells were studied.Firstly,the effect of CsI solution post-treatment on MAPbI₃ thin films and solar cells was studied.When the concentration of CsI solution was 6.0 mg/ml,the MAPbI₃ is recrystallized,?m-sized grain film with high surface coverage is obtained,and the roughness of the films is reduced,as well the photoluminescence is enhanced by reducing the internal defects.The efficiency of the solar cells increased from 10.5%to 15.3%.Secondly,the effect of NaI/KI solution post-treatment on t MAPbI₃ thin films was studied.Both of them can also induce the second crystallization of the films and increase the grain size to the micron level.When NaI/KI solution concentration is 1.6 mg/ml and 1.4 mg/ml respectively,the internal defects were reduced significantly,and the photoluminescence intensity was the highest,but the band gap of the films after post-treatment has little change.