The Performances Of Perovskite Solar Cells Enhanced By Doping And Interface Modification

Perovskite solar cells（PSCs）were successfully prepared for the first time in 2009,the initial power conversion efficiency（PCE）was only 3.8%.Due to many excellent properties of perovskite materials such as high optical absorption coefficient,long carrier mobility as well as direct and adjustable optical band gap,once discovered,it attracts wide attention from researchers all over the world and developed rapidly.Nowdays,the latest internationally certified PCE of PSCs has up to 25.7%,which shows a great commercial application prospect.At present,stability and PCE are the two major problems to be faced in its commercialization process.Moreover,they largely depend on the quality of perovskite film.Therefore,in this paper,the grain boundary passivation,interface modification,bulk/surface joint modification,and post-treatment method were adopted to improve the quality of the MAPbI₃ film.The effects of different modification methods on the crystal growth,interface and surface were discussed systematically.The regulation mechanism was disclosed.Finally,high-quality and dense MAPbI₃ films with large crystal size as well as suppressed boundary and interface defects were reached successfully.And as a result,the PCE and stability of PSCs were improved markedly.The main research contents are shown as follows:1.8-hydroxyquinolone lead（Pbq₂）contained Pyridine nitrogen,C-O bonds and quinoline ring was doped into the MAPbI₃ perovskite film to fabricate PSCs doped with pbq₂.The growth of perovskite crystals was regulated by the simultaneous interaction between the above functional groups in pbq₂ with Pb²⁺,MA⁺,and I^-in perovskite.At the same time,pbq₂ chelated at the perovskite grain boundary,which passivates the defects and inhibits the photo-carriers non-radiative recombination and ion migration at the grain boundary.And as a result,the high-quality and dense perovskite films with large grain size was obtained.On the other hand,the conductive band energy barrier between perovskite layer with Sn O₂ layer interface was reduced by the pbq₂ doping,which accelerates the separation and transportation of carriers at the electron transfer layer（ETL）/perovskite layer interface.Finally,the average PCE of PSCs with high environmental stability was improved significantly from 17.17%of the original sample to 19.67%.2.The efficient and stable PSCs was successcully produced by using bathocuproine（BCP）bilateral-modified perovskite layer.The wide band gap n-type semiconductor BCP was adopted to simultaneously modify the bottom（Sn O₂ layer ETL）/Perovskite)and the top interfaces（Perovskite/Spiro-OMe TAD layer（Hole Transport Layer,HTL））of perovskite film.In this method,the perovskite growth was controlled by the interaction between the pyridine nitrogen in BCP molecule and Pb²⁺ions in perovskite crystal,which leads to high-quality and dense perovskite film.At the same time,the thin BCP molecular modification layers were formed simultaneously on the top and bottom interfaces of the perovskite film,which passivates the Pb²⁺defects and forms a wide and suitable energy bairrier（CB:-3.5 eV–VB:-7.0 eV）,which can inhibit the non-radiative recombination and promote the separation and tunneling transmission of carriers at the bottom/top interfaces of the perovskite layer.And as a result,the PCE of PSCs increased from 17.5%to 20.6%.Moreover,due to the good hydrophobicity of BCP molecules,the stability of PSCs with BCP bilateral modification was greatly improved.Its PCE was remained at 91.4%of the original value,which is much better than 78.3%of the reference PSCs after aging for 144 hours at 20℃and RH 25%in air condition.3.A kind of joint modification method by doping with CsPbBr₃ QDs in bulk and surface treatment with phenylethylamine iodide（PEAI）was proposed.Firstly,the inorganic perovskite quantum dots（CsPbBr₃ QDs）was doped into MAPbI₃ perovskite film by anti-solution.It can regulate crystallization process of MAPbI₃ as nucleations with bigger grain size,the Cs⁺and Br^-can enter into the perovskite grain and reduce the bulk defects,and as a result,dense MA_1-xCs_xPbI_3-yBr_y perovskite film was reached.Secondly,the PEAI was used to modify the surface（including grain boundary and interface）of the doped perovskite film.Then,a PEAI thin barrier layer was formed on its top surface,which reduces the surface defect density in the perovskite crystal,and as a result,the non-radiative recombination of carriers was reduced.On the other hand,the PEAI layer can block the direct contact between HTL and ETL in the interval,form a high-energy barrier,which can inhibit the leakage current and promote carrier transmission in PSCs.Therefore,the joint modification strategy significantly improved the PCE of PSCs from 17.21%to 21.04%,and effectively enhanced its stability in air condition.4.Zn²⁺doped CsPbBr₃ QDs（CsPbBr₃:ZnQDs）with high quality and low defects were successfully prepared firstly,which is then used to modify MAPbI₃ perovskite films by post treatment to produce CsPbBr₃:ZnQDs post-treated PSCs.Both the bulk and surface defects in perovskite films were passivated by only one-step post treatment process.Therefore,the passivation process of perovskite films is largely simplified.CsPbBr₃:ZnQDs played a dual regulation role of Zn²⁺ions and CsPbBr₃ QDs on MAPbI₃ system.The Cs⁺,Br^-and Zn²⁺was released from surface of the spin-coated QDs to the bottom MAPbI₃ layer to passivate defects both in bulk and surface of MAPbI₃.The crystallinity was ehanced and at the same time,MA_1-xCs_xPbI_3-yBr_y:Zn barrier layer on the upper layer of MAPbI₃ film was also formed,which reduces the energy level barrier between the valence band of perovskite layer and HTL,and accelerates the hole separation and transportation at this interface.Therefore,the PCE of the PSCs post-treated by CsPbBr₃:ZnQDs was increased from 17.56%in reference device to 21.07%.In addition,the chelation of hydrophobic oleamine and oleic acid molecules on the surface target MAPbI₃film improved its hydrophobicity（82.5°）.And as a result,as-prepared PSCs showed a high environmental stability.After aging for 50 days in20℃and RH 25%air,its PCE still maintained at 77.5%of the initial value,which is much better than 51.3%of the reference PSCs.