Film And Interface Modification Towards The Chemical Stability Of Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells（PSCs）have achieved a very fast development in recent years,which benefits from its advantages of high conversion efficiency,low-cost and easy-preparation technique.Interface modification is an effective approach to further improve the power conversion efficiency and stability of PSCs.Here,in order to solve the key scientific problems such as the corrosion of the perovskite layer induced by the smaller polar molecules in hole transport materials（HTM）,the charge carrier recombination at the interface between the perovskite and HTM layer,we carried out the research on the interface engineering.Likewise,to sort out the problems including the lower coverage of the film,the residual of solvent with high boiling,the poor crystallized quality,and the higher trap density of the thin film,etc.We conducted the investigation by means of solvent engineering and endeavored to prepared the perovskite thin film with higher crystallization and orientation.The main results and conclusions are as follows:（1）The effects of MMT as surface modifier on perovskite films were investigated.UV-vis result showed that the TBP as additive in HTM could corrode the perovskite thin film and thereby deteriorate the stability of the solar cells.XRD results revealed that TBP was demonstrated to be intercalated in the MMT structure by means of hydrogen bond between molecular,which could effectively prevent the perovskite layer from corrosion.A delayed corrosion led to an increased current density owing to the enhanced absorption,while a reduced charge recombination led to an increased fill factor and open voltage circuit values.Consequently,the corresponding efficiency increased from 9.0%to 11.9%.（2）The dimethyl sulfoxide（DMSO）solvent was introduced into precursor solution and its effect on perovskite thin films was then studied.XRD results revealed that the dimethylformamide（DMF）by additional solvent of DMSO could retard the crystallization of PbI₂,which was proved to be capable of coordinating with PbI₂ by coordinate covalent bond.The complexes of PbI₂（DMSO）_x（0≤x≤1.86）was confirmed by XPS and TGA measurement.Afterward,an intramolecular exchange of DMSO with CH₃NH₃I（MAI）enabled the complexes to deform their shape and finally to reorganize to be an ultraflat and dense perovskite thin film.The controllable grain morphology of perovskite thin film allows obtaining a power conversion efficiency（PCE）above 17%.And then,we introduced DE to remove the residual DMSO via formation an azeotropic mixture.Consequently,the perovskite films and devices with better thermal stablity and higher efficiency are obtained.（3）The high quality crystal perovskite film was obtained using MA_2.5PbI₃Cl_1.5·2H₂O as precursor and the mechanism of the perovskite process was studied.In the present work,highly-orientated perovskite thin films(MAPbI_3-xCl_x)are prepared by means of aquo-intermediates-assisted solution-process.It displayed super-duper preferred-orientation along<110>direction that was close to the single crystal,and its aspect ratio of（110）/（310）was nearly two orders of magnitude higher in contrast to the films that prepared by traditional way.Owing to its superior performances,e.g.,highly crystallized quality,stress-free inside films,longer electron lifetime,faster temporal response time etc,the highly-orientated perovskite-based solar cells accordingly allowed realizing high efficiency while improving its thermal stability.