The Influence Of Regulation Of Hole Transport Layer On The Perovskite Active Layer And Performance Of Perovskite-based Optoelectronic Devices

Recently,due to high light absorption coefficient,large carrier diffusion length,high defect tolerance direct band gap,continuously adjustable band gap and high fluorescence quantum yield,metal halide perovskite materials have been widly used in optoelectronic devices,which become a focused hot in the materials filed both at home and abroad.As representative of optoelectronic devces,perovskite solar cells（PeSCs）and perovskite light emitting diodes（Pe LEDs）have a wild application prosect owing to their constantly updated efficiency limits.PeSC and Pe LED are similar in structure,mainly composed of perovskite active layer,transport layer and electrode.In this dissertation,we investigated PIN planar PeSCs and Pe LEDs as model to explore the influence of regulation of hole transport layer（HTL）on the perovskite active layer and performance of perovskite-based optoelectronic devices.In view of the existing bottleneck problems such as lack of hole transport materials,poor hole extraction ability,energy level mistach.In this dissertation,the optoelectronic characteristics of HTL are regulated from the aspects such as doping engineering,materials engineering,solvent engineering and film post-treatment engineering,while the crystallization condition of the perovskite active layer is improved,in order to improve the efficiency and stability of perovskite optoelectronic devices.The dissertation consists of the following four parts:1.Influence of HTL doping with PMAA on the performance of PeSCs devicesThe insulating polymer polymethyl methacrylate（PMMA）was firstly doped into p-type polymer polytriarylamine（PTAA）as a mixed hole transport layer to prepare PIN type PeSCs.The introduction of PMMA can resist the roll-off of conductivity caused by the necessary UV ozone-treated（UVO）treatment.Compared to PeSCs without PMMA doping,the efficiency and stability of PMMA doped devices are significantly improved.After optimizing the concentration of PMMA,the maximum power conversion efficiency（PCE）of the device can reach 14.56%,which is 33%higher than that of the control group（10.92%）.The performance improvement can be attributed to the high conductivity of the mixed cavity transport layer doped with PMMA after UVO treatment,and the optimized crystallization properties of perovskite.Meanwhile,residual Pb I₂ can further passivate perovskite,which is also benficial to the device performance.The mixed HTL has better ability to block moisture from penetrating into the perovskite layer than pure PTAA layer.Hence,PeSCs based mixed HTL could keep good stability,retaining 80%of their initial performance after 700 hs.2.Effect of organic small molecules as HTL on the performance of PeSCs devicesIn the preparation of PIN-type PeSCs,it is necessary to select an appropriate p-type semiconductive material as HTL,which will determine the crystallization quality of the subsequent perovskite films and hole charge extraction at the perovskite/HTL interface.Herein,organic small molecule N,N-Bis（3-methylphenyl）-N,N-bis（phenyl）benzidine（TPD）as the hole transport layer was first used as HTL in the fabrication of PeSCs.It achieves a peak PCE of 19.77%by optimizing the thickness,which is about 1.4 times higher than the PeSCs employing poly（3,4-ethylenedioxythiophene）-poly（styrenesulfonate）（PEDOT:PSS）as HTL.The excellent photovoltaic performance can be attributed to the high hole mobility,relatively matched HOMO level of TPD film,and good crystralinity of the perovskite active layer deposited on it.Due to the hydrophobicity of TPD film,The TPD-based PeSCs have excellent environmental stability.3.Study on the effect of ethanolamine doping PEDOT:PSS on the performance of PeSCsAs a common hole transport material,PEDOT:PSS has excellent electrical conductivity,visible light transparency,and high quality film prepared by wet process.,which can be used as HTL in the fabrication of PeSCs.However,PEDOT:PSS has a low work function of-4.9-5.2 e V,which doesn’t match the conduction band of the perovskite active layer based on MAPb I₃（-5.4 e V）,which may lead to a severe energy loss of PIN type PeSCs.It usually results in a poor open-circuit voltage of the device（<1V）.Herein,ethanolamine（ETA）was introduced to modify the PEDOT:PSS in the first time.The modified PEDOT:PSS rendered a deeper work function,from-5.1 e V to-5.35e V,which is more suitable for the hole extraction from the perovskite to HTL.Hence,the results show that the open-circuit voltage of the device increases from 0.99 V to 1.06V,and the corresponding PCE increases from 14.68%to 19.16%.The alkaline nature of ethanolamine greatly neutralizes the acidic of PEDOT:PSS,and plays a role in protecting the anode,leading to a significant improvement in the stability of the devices.After stored for 2000 hours,the PCE of doped devices can maintain 84.2%of the initial value,which is much higher than 67.1%of undoped devices.4.The effect of alcohol solvent treatment on the performance of Pe LEDsMethanol（Me OH）with high dielectric constant and high hydrophiliciy was introdected to treat the surface of PEDOT:PSS as HTL in th fabrication of Pe LEDs,which leads to the significant increase in the conductivity of film surfaces.The Me OH treated PEDOT:PSS layer improves the hole injection through reducing the contact barrier between the HTL and the CH₃NH₃Pb Br₃ emitting layer without sacrificing the quality of the perovskite film.Hence,the turn-on voltage of Pe LED is reduced from 3.3V to 2.4 V.The maximum brightness of Pe LED is increased from 201 cd/m² to 1565cd/m² via Me OH treatment.Besides,green environment-friendly solvent isopropyl alcohol（IPA）was employed instead of cholrobenzene（CB）as anti-solvent to make perovskite crystallize more quickly in the fabrication of perovskite films,with smaller grains and faseter exciton radiation recombination.The device prepared by IPA achieve the maximum brightness of 7960 cd/m² and current efficiency of 2.2 cd/A,which is 1.5and 2.2 times than that CB devices,respectively.In summary,this work explored the effect of hole transport layer modification including polymer and solvent doping,new p-type organic small molecule,alcohol post treatment on PeSCs and Pe LEDs from different perspectives,and proposed a new straget to optimize the overall performance of devices including lifetime,which provided paractical strategies for the large-scale commercial application of perovskite optoelectronic devices.