Effect Of Interface Modification On Performance Of CH₃NH₃PbI₃ Perovskite Solar Cells

The energy crisis and environmental pollution are becoming more and more serious,so developing clean energy to replace traditional energy has become an important task around the world.Solar energy is exhaustless,clean and renewable.Therefore it is crucial to develop solar cells to alleviate above-mentioned problems.Developing solar cells vigorously is a project that benefits all mankind.In 2009,a kind of solar cell prepared by a new material was born and attracted the attention of correlative researchers.It is the first perovskite solar cell based on the structure of CH₃NH₃PbX₃.After that,perovskite solar cells have been developed widely.So far,the highest efficiency of perovskite solar cells has reached 25.7%.Although the perovskite solar cells develop rapidly,there are still many factors that affect the commercialization of them,such as the polycrystalline perovskite film which lead to defects and grain boundaries,low carrier mobility between the perovskite layer and the transport layer,and the decomposition of perovskite film in the air.In this paper,CH₃NH₃PbI₃(MAPbI₃)perovskite solar cells were mainly studied from the interface modification.The main contents of the paper are as follow:(1)A simple solution spin-coating method was used to place KCl modification layers with different concentrations at the SnO₂/MAPbI₃ interface.Through the optimization of the modification layers,it is found that the grain size of the MAPbI₃ is the largest and the distribution of grains is the most uniform when the concentration of KCl modification layer is 2 mg/mL.The devices modified by 2 mg/mL KCl modification layer were prepared and performed.The modification layer induces crystallization to enlarge the grains and reduce the number of grain boundaries.K ions from the modification layer diffuse into the perovskite film and passivate the grain boundaries to improve the morphology of the perovskite active layer.The non-radiative recombination caused by defects is reduced while the extraction and transport of carriers at the interface are enhanced,thus the performance of devices are improved.The V_OC,J_SC,FF and PCE of the optimized device were 1.12 V,21.13 mA/cm~2,0.72and 17.09%,respectively.The KCl modification layer significantly improves the open circuit voltage(V_OC)and fill factor(FF),and suppresses the hysteresis of devices.Meanwhile,the air stability of the device is also improved.(2)CsPbBr_xI_3-x perovskite nanocrystals(NCs)with different Br/I ratios were successfully prepared,and they were dispersed in toluene as the modification layers and coated on MAPbI₃ films.The grain sizes of MAPbI₃ films modified by different nanocrystals were almost the same with unmodified MAPbI₃ film,but the surface roughness of modified MAPbI₃ films were reduced and the modified surfaces were smoother.Then,the effect of CsPbBr_xI_3-x NCs on the stability of MAPbI₃ films were studied.It was found that the NCs modification layers reduced the surface roughness of MAPbI₃ films thus the hydrophobicity of MAPbI₃ films was also improved.The energy level arrangement of the films modified by the interface layers was studied,the positions of the valence band top(VBM)of CsPbBr_xI_3-x NCs with different Br/I ratios were measured,and the effect of Br/I ratio on the energy band was analyzed.(3)The synthesized CsPbBr_xI_3-x NCs were introduced between the MAPbI₃ light-absorbing layer and Spiro-OMe TAD layer as the modified layer to prepare perovskite solar cells.The J-V curves of devices modified by CsPbBr_xI_3-x NCs of different Br/I ratios show that the CsPbBr_1.2I_1.8 NCs modified device is the champion device with the highest efficiency of 19.16%,while V_OC,J_SC and FF are 1.13 V and 22.70 mA/cm~2 and0.75.And the hysteresis of the CsPbBr_1.2I_1.8 NCs modified device is negligible.At the same time,the air stability of the champion device was studied.Since the CsPbBr_1.2I_1.8NCs modification layer enhanced the hydrophobicity of the MAPbI₃ film and delayed the degradation of the device.The efficiency of NCs modified device only decreased from 19.16%to 17.16%within 25 days,so the CsPbBr_1.2I_1.8 NCs modification layer improves the stability of the device.Through a series of carrier dynamics characterizations,it is found that the CsPbBr_1.2I_1.8 NCs modification layer passivated the surface defects of the MAPbI₃ active layer,reduced the defect density of the film,inhibited the carrier recombination at the interface and accelerated the extraction of holes.Thereby improving device performance.