Organic Coordinative Solvent-assisted Preparation Of High Quality Perovskite Films And Their Photovoltaic Performance

In the past few years,the efficiency of organic-inorganic hybrid perovskite solar cells(PSCs)has zoomed from 3.8%in 2009 to the current world record of 22.1%.The rapid improvement has been attributed to exceptional photoelectric properties of perovskite materials,including adjustable bandgap,ambipolar charge transport,quite long electron and hole diffusion length,high light absorption coefficient.Besides the high power conversion efficiency,the perovskite solar cells possess low cost and solution processability,making them a promising candidate to replace the existing commercial PV technologies.High quality perovskite films are prerequisite for achieving high performance PSCs.Solvent engineering,which introduces DMSO into perovskite precursor solution and can produce high quality perovskite films with large grains and no pinholes,has received increasing attention.However,previous studies have demonstrated that the ratio of PbI2/DMSO in the precursor solution must be constrained to a quite narrow window around 1:1 for high quality perovskite films.At present,it was still unclear why the ratio of PbI2/DMSO could not been enlarged.Besides,the composition of crucial intermediate was just speculated by XRD,FTIR and element analysis,and its detailed structure is still unclear.Thus,understanding the impact of DMSO on perovskite film quality from the molecule level was conducive to both further optimizing the solvent engineering and developing a new method to deposit the perovskite films.The stability and reproducibility of PSCs have been major obstacles towards their industrialization.The pure perovskite compounds that is suitable for PV applications,primarily MAPbX3,FAPbX3 and CsPbX3(X = Br-,I-),show numerous disadvan-tages.Recently,mixing cations and halides has become an important design principle to achieve perovskite compounds with improved thermal and structural stability.Therefore,it is beneficial to further improve the stability and efficiency of devices for us to develop different process of depositing the mixed-cations perovskite films.This thesis takes organic-inorganic hybrid perovskite solar cells as our research object,and main contents are showed as follows:First,understanding the impact of DMSO on perovskite film quality from the molecule level.We captured some intermediate single crystals and resolved their crystal structures.Then,combining with some characterizations of SEM,XRD and TGA,we invesigated the impact of DMSO on perovskite film quality from the molecule level.Based on the above research,we hope for further optimizing the solvent engineering or developing a new method to deposite perovskite films.Second,NMP-assisted preparation of high quality perovskite films.Single crystal measurement verified that just one kind of complex PbI2·NMP could form when we used NMP as solvent to dissolve PbI2 and grow crystals.And XRD measurement also demonstrated that only one kind of precursor film formed whatever the ratio of PbI2/NMP in the precursor solution was.The results indicated there was a wider additive window with NMP as the coordinative solvent,which would make the fabricaion process of devices more controllable.As a result,regardless of the ratio of PbI2/NMP in the precursor solution and the deposition methods,the final perovskite films all displayed dense and uniform morphology,and the performance of devices was also decent.Third,exploring the deposition process of cesium-containing triple cation perovskite films.We developed sequential two-step method to deposite cesium-containing triple cation perovskite films and screened out the optimal content of CsI in the precursor solution by performance mesurement of devices,Futher stability test demonstrated the introduction of Cs greatly improved the stability of devices.Fourth,summary and perspective.In this section,we summarized the results and shortages of this thesis,and looked forward to the next research.