Study Of The Effect Of Different Deposition Method Of Organic-inorganic Hybrid Perovskite CH₃NH₃PbI₃ On Solar Cell Performance

Perovskite can be used as an excellent light absorber in solar cell mostly due to its good physical properties,such as nonlinear optical characteristics,electroluminescent,magnetic conduction,direct bandgap,large absorption coefficient,high carrier mobility and low emissivity carrier recombination rate.Perovskite combining with FTO glass,n-type semiconductor TiO2,hole transporting material and counter electrode are the main part of the perovskite based solar cell.In this device,perovskite plays as the light absorber,and generated exactions.The surface morphology of the film has a great influence on the optical and physical properties.For instance,the lighe-absorbing,charge transport and exction diffusion length are closely related to the crystallization properties of perovskite.The microcrystalline defects and grain boundaries of perovskite crystal can act as charge traps,increasing the charge combination.Due to the crystallinity and grain boundary of perovskite,hysteresis in the evaluation of cell efficiency is not accurate.Thus the performance of the cell is greatly influenced by the surface morphology of perovskite.Herein,we mainly fabricated perovskite thin films by different methods to optimize its morphology,regularity and uniformity in order to increase conversion efficiency of the solar cell.The research contents and conclusions are as follows:(1)The solution whit equivalent ratio of PbI2 and CH3NH3I(40 wt%diluted in DMF)was deposited on TiO2 anode by spin coating.After annealing,carbon ink was deposited directly on the top of the CH3NH3PbI3 by blade coating to form the counter electrodes.X-ray,scanning electron microscopy and UV-visible spectrophotometer were used to analysis the properties of perovskite thin films.The results suggested that after annealed under certain conditions of temperature,the fill rates on the surface of the thin films fabricated by one step solution method is relatively low.Its morphology is uneven,and roughness is bigger.The efficiency of perovskite based solar cells obtained by this method is 3.5%.It is mainly because that the porosity of the film obtained by this method is relatively large.The separated eletron could not transport effectively.Moreover,it made the TiO2 contact with the carbon counter electrode directly,which increasd the recombination of electron and hole.(2)One layer of PbI2 was deposited on the mesoporous TiO2 films by spin coating firstly.Then the films were dipped in a solution of CH3NH3I in isopropanol to obtain a crystallographic perovslite film,and assembled into the solar cell.X-ray,scanning electron microscopy and UV-visible spectrophotometer was also introduced to analysis the properties of the perovskite thin films.The results revealed that the thin films fabricated by the two step solution method has higher surface coverage.Its grain is closely connected with each other,and the hole fill rate was also higher.After optimizing,the cell efficiency of the perovskite based solar cell fabricated by this methods is 4.36%.This is mainly because that the morphology of thin films prepared by this mothod were compact and inerratic,which is beneficial to the charge transport.(3)One layer of PbI2 was deposited on the mesoporous TiO2 films by spin coating.Then the films were surrounded by some sprinkling white crystals of CH3NH3I under the sealed vacuum conditions,insulating at 150 ℃ for 3 hours.The fabricated method of the solar cell was as the same as the above.According to the test results,we found that the perovskite crystals are large in these planar structured perovskite solar cells.Its grain boundary is less,with high degree of regularity.The highest efficiency of perovskite based solar cell prepared by this the method is 3.59%.The large crystal and isdense morphology will promote the charge transport.(4)Perovskite thin film were prepared by these three different deposition methods to fabricated the perovskite based solar cell without any hole transporting materials,and using commercial carbon ink as a counter electrode.Overall,the cell efficiency is low on account of the lower fill rate.Using the carbon counter electrode by the blade coating method,may increase the series resistance of the devises,generally resulting a lower efficiencies of the solar cells.