Research On The Key Materials In Perovskite Solar Cells

The performance improvement of solar cells mostly due to the update of fabrication process and cell structure.However,the application of new materials is the key point to settle such problem.The perovskite solar cells still face the problems of poor stability,high cost and further improvement of efficiency.The fundamental way to improve device performance is still the material problem for the development.Researches targeted on the controllable material synthesis,device design,device mechanism.This work mainly studies the electron transfer layer with one-dimensional TiO2 nanostructures and light-absorbing layer.The purpose is to reveal the key factors that affect the performance of solar cells and to cut down the cost in the condition of improving photo-to-electron conversion efficiency.Research on the electron transport layer based on one-dimensional TiO2 nanowire structure.Due to the advantages of providing direct electron transport channels for photogenerated electrons and high electron transfer rates,the one-dimensional TiO2 nanowire arrays have been widely used in the optoelectronic devices.However,the one-dimensional nanowire is tend to cluster while grow,make it hard for perovskite penetration.The defects on the nanowire surface make it harmful to perovskite deposition.In this study,hydrothermal method was firstly used to prepare uniformly nanowires arrays.The influence of the parameters such as the titanium isopropoxide(TIP)concentration and growth time on the morphology was investigated.The growth mechanism was discussed.By adoting the etch and anneal process,the cluster and surface state of TiO2 nanowire arrays was optimized and the formation mechanism of pores on the nanowires surface was clarified.The efficiency of the perovskite solar cells based on the porous one-dimensional TiO2 nanowires and perovskite film of bad quality was 2.24%,which is not superior than device based on mesoporous TiO2 nanocrystals.The improvement of perovskite film quality by using the halogen-free lead source.The Pb(CH3COO)2 and PbI:are common lead precursors for the CH3NH3PbI3 thin films preparation in the present study.The use of Pb(CH3COO)2 can accelerate the growth rate of perovskite films,and then control the morphology of the films.Since CH3NH3PbI3 film prepared by the two-step method is usually made of stacked CH3NH3PbI3 particles,pores between the inter-particle will cause the direct contact of the electron transport layer and the hole transport layer.In this study,Pb(CH3COO)2 and PbI2 composite lead sources were used to improve the low coverage of perovskite films prepared by two-step method.The influence of lead source on the crystallization,morphology,light absorption properties and photoelectric properties of perovskite solar cells was revealed.The carrier transfer characteristics were further discussed.It was found that Pb(CH3COO)2 can effectively improve the poor coverage of the perovskite film prepared by the two-step method.The amount of residual PbI2 at the mesoporous TiO2/CH3NH3Pbl3 interface is also effectively controlled by changing the Pb(CH3COO)2 concentration.The results show that the proper amount of PbI2 residues can not only passivate defects on the mesoporous TiO2 surface,but also ensure the efficient transfer of photoelectrons.On the other hand,it can suppress carrier recombination because the conduct band of PbI2 is higher than CH3NH3PbI3.The perovskite solar cell obtained 15%improvement o efficiency by using two-step solution process.By one-step anti-solvent method,the average photoelectric conversion efficiency was also improved by 10%(from 13.6%to 15.0%),the open circuit voltage improvement of about 70 mV has been achieved.Achieving perovskite solar cells based on halogen-mixed perovskite via low pressure vapor-assisted solution process.Compact,flat and pinhole-free perovskite film could be efficiently prepared by low pressure vapor-assisted solution process.Flat perovskite solar cells based on the film can achieve good optoelectronic performance.In this study,PbI2 is used as precursor of lead source,pure CH3NH3Cl/CH3NH3Br was used to prepare perovskite films.The influence of reaction temperature on the crystal structure,surface morphology,light absorption properties of perovskite films and photoelectric properties of perovskite solar cells has been studied.Then,the perovskite films were prepared by using CH3NH3CI:CH3NH3I and CH3NH3Br:CH3NH3I mixed amine salts respectively.The influence of CH3NH3Cl/CH3NH3Br content on the crystal structure,surface morphology,light absorption properties and photoelectric properties of perovskite films was investigated.The results show that the perovskite constituted of CH3NH3PbCl3:CH3NH3PbI3 mixed phase is obtained when CH3NH3Cl is used,whereas CH3NH3PbBr3-xI-x with different Br doping amount is obtained when CH3NH3Br is used.Through the control of amine salt,the doping amount of halogen in CH3NH3PbI3 film can be controlled,and the perovskite film with excellent film uniformity and crystallinity can be obtained.The film has adjustable visible light absorption characteristics and diversified device performances.The fluorescence lifetime of CH3NH3Pbl3-xClx films is longer than CH3NH3PbBr3-xIx films.The efficiency of perovskite solar cells based on CH3NH3PbI3-xClx films is generally higher than that of CH3NH3PbBr3-xIx films.Using 15 wt%CH3NH3Cl:CH3NH3I to prepare perovskite films,perovskite solar cell with the highest efficiency of 17.3%was achieved,which was 21%more efficient than perovskite solar cell based on pure MAPbI3.Meanwhile,device based on CH3NH3PbBr3-xIx behaves better stability under continuous illumination of AM1.5G.Preparation of CH3NH3PbCl3 film via low pressure vapor-assisted solution process.Flat,dense and pinhole-free CH3NH3PbCI3 film was prepared using PbI2 as precursors.The thin films consisted of grains with an average size about 1.5 ?m.This work solves the problem of low solubility of PbC12 and serious contamination of PbC12 film by vapor deposition when prepare CH3NH3PbCl3 film by solution method.During the vapor reaction,the I element introduced by PbI2 is gradually replaced by the Cl element in CH3NH3Cl,and the pure CH3NH3PbC13 film can be finally obtained.The photodetector based on this film achieves an optimum response of 297 ?A/W at 2 mW/cm2.