Defect Control Of Perovskite Solar Cells And Optimization Of The Composition Of Hole Transport Layer

Since the appearance of the perovskite solar cells（PSCs）in 2009,rely on its excellent photoelectric performance and huge development potential,the photoelectric conversion efficiency（PCE）has grown rapidly from 3.8%to 25.2%certified by NREL in the past 11 years.However,there are many problems that need to be solved,for example,at the interface between the perovskite light-absorbing layer and the hole transport layer（HTL）,the large number of defects and poor energy level matching will resulting in low hole mobility and plentiful carrier recombination,then preventing further improvement in device performance.The hole transport layer needs to be modified due to the inherent properties of its material.This article focuses on the modification of the interface between the perovskite layer and HTL,and the hole transport material from different directions.The main research contents and conclusions are as follows:（1）We introduced iodobenzene diacetate（DAIB）to the interface between the perovskite layer and HTL to modify the interface layer and optimize the surface of the perovskite layer by eliminating formamidine iodide（FAI）,which is unfavorable for device performance.We first clarified the reaction mechanism between DAIB and FAI through the solution reaction,¹H-NMR and FTIR tests.The observation of the surface morphology of the perovskite thin film and XRD,XPS tests proved that the introduction of DAIB will not adversely affect the formation and crystallinity of the perovskite thin film,and effectively reduced the FAI on the surface of the perovskite layer.The UV-vis,UPS,PL,TRPL,defect density,and EIS tests have proved that the energy level of the modified perovskite layer is more conducive to carrier migration,fewer surface defects on the perovskite layer,and reduced non-radiative recombination.The hole transport performance was successfully optimized.In the end,the modification not only significantly improved the photovoltaic performance parameters,but also improved its repeatability and stability to light,water and oxygen.The PCE of the best device reached 20.08%.（2）We introduced lanthanum acetylacetonate（La（acac）₃）as an interface treatment agent at the interface between the perovskite layer and HTL to reduce surface defects caused by lead iodide（PbI2）accumulated on the surface of the perovskite layer.We first observed the cross-section of PSCs and the surface morphology of the perovskite film by FESEM and AFM,and tested the perovskite film by XRD,XPS.The results show that the introduction of La（acac）3 does not affect the film-forming property and crystallinity of the perovskite layer.Moreover,it reduced the roughness and defects of the perovskite layer.The UV-vis absorption spectroscopy,UPS,PL,TRPL,defect density and EIS tests proved that the energy level of the modified perovskite layer is beneficial to carrier migration,and the defect density of the perovskite layer is reduced.Nonradiative recombination is reduced and hole transport performance is optimized.The results show that not only the photovoltaic performance parameters of the modified device have been significantly improved,but the hysteresis effect has also been improved.Finally,a PCE of 20.10%was achieved.（3）We introduced potassium ferricyanide（K3[Fe（CN）6]）as an additive to the Spiro-OMeTAD solution to promote its oxidation.The UV-vis absorption spectrum showed that K3[Fe（CN）6]successfully pre-oxidized Spiro-OMeTAD.Tests by UPS,PL,TRPL,EIS,and defect density show that the doped-HTL has enhanced hole extraction capability,less carrier recombination inside the device,and better hole transport performance.The tests of the J-V curve and the steady-state output prove that the introduce of the K3[Fe（CN）6]not only greatly improved the PCE,the photovoltaic performance parameters are significantly improved,but also reduces the hysteresis effect of the device.At the same time,the current output was more stable.The doped device eventually reached a best PCE of 20.65%.