| Under the pressure of global energy crisis and environmental issues,clean energy draws great attention of researchers.As a significant member of new energy,solar energy could effectively relieve the energy crisis and environmental issues.Solar cells play an irreplaceable role in utilization of solar energy.However,the problems of high cost and complex fabricating process in traditional silicon-based solar cells are still in need to be solved.And among new-generation of solar cells,perovskite solar cells have a great potential of replacing silicon-based solar cells based on the advantages like long carrier diffusion length,tunable band gap,large optical absorption coefficient and simple fabricating process,etc.Since 2009,perovskite solar cells have a great breakthrough in power conversion efficiency which is now comparable to silicon-based solar cells.And such a rapid development make perovskite a promising candidate for the next-generation solar cells.Presently,there remains several problems to be solved,and one of the problems is hysteresis that will cause an over-or under-estimate of device efficiency.In terms of the origins of hysteresis,the main view claims that the hysteresis is induced by the ion migration and the charge trapping and de-trapping process.In this work,2-aminoethanesulfonamide hydrochloride(ASCl)was doped into perovskite to eliminating hysteresis.Correspondingly,the average efficiency resulted from forward scan and reverse scan was increased.The results of testing cells with different scan rate indicate that the doped cells have no hysteresis under any scan rate,which conformed the elimination of hysteresis.Besides,both the optical stability of devices and the moisture stability of perovskite films were improved after doping.In order to analyze the mechanism of the doping-induced elimination of hysteresis in this work,many characterizations of perovskite films were carried out.The morphology test results indicated that the perovskite crystals arrayed denser and the crystal size became more uniform after doping,and the roughness of the film decreased.The results of surface element analysis suggested that the dopant distributed uniformly on the surface of perovskite.The X-ray photoelectron spectroscopy test revealed the coordination between dopants and defects,which indicated that the defects were passivated.The fluorescence spectrum test showed that the perovskite after doping had stronger fluorescence intensity and longer fluorescence lifetime.Such result demonstrated the decreased defect-induced non-radiation recombination,which was coincide with the passivation to defects.The result of X-ray diffraction test indicated the improved crystallinity of perovskite after doping.Combining the molecular structure of dopant,it was revealed that the elimination of hysteresis was due to the improved crystallinity of perovskite and the passivation to defects,which could decrease the amount and activity of defects.Such improvement was rooted in the sulfoxide “S=O” group.We have also designed and synthesized several small molecule materials as hole transport layer.The HOMO levels provided by cyclic voltammetry test suggest that these new HTMs have a good alignment of energy level with perovskite.The efficiency test results indicated that the devices based the new HTMs could work normally,even though the present efficiency still lower than the cells based on the traditional HTM spiro-OMeTAD.We speculated that the bad results were ascribed to the low hole mobility of the new HTMs which lead to low fill factor.However,such results paved the way for adjustments to the molecule of new HTMs. |
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