| In recent years,organic-inorganic hybrid perovskite materials with ABX3 structure are considered as one of the most promising photoelectric materials in the future due to their high optical absorption coefficient,high carrier mobility and simple synthesis method.Perovskite-based PSCs are a new and efficient organic-inorganic hybrid solar cell.Compared with traditional silicon-based or copper-indium-gallium-selenium thin film photovoltaic devices,PSCs have the advantages of high efficiency,low cost,flexibility and easy preparation.The photoelectric conversion efficiency of perovskite solar cells(PSCs)has increased from 3.8%in 2009 to 23.7%in 2019.Although great breakthroughs have been made in the photoelectric conversion efficiency of PSCs,the stability of PSCs is still a big problem compared with traditional photovoltaic devices.The lack of stability of PSCs has cast a shadow on its future large-scale production and practical application.During the research period,I focused on several aspects of stability of PSCs.Our results show that the optimization of perovskite photoactive materials in terms of structural stability,thermal stability,environmental stability and light stability is the key to the further practicality of PSCs.The highly efficient and stable PSCs can be prepared by reasonably designing perovskite composition and optimizing carrier interface modification.(1)Firstly,on the basis of the PSCs with normal planar structure,we introduce hydrophobic zinc phthalocyanine(ZnPc)material with a thickness of 80 nm as a hole modification layer inside the device,which greatly improves the stability and photoelectric conversion efficiency of PSCs devices.In terms of stability,the device can maintain an initial efficiency of more than 90%after 2400 hours in ambition conditions.In the aspect of photoelectric conversion efficiency,the introduction of ZnPc can improve the optical absorption and absorption of the device,and make the photoelectric conversion efficiency increase from the initial 15.1%to 16.8%.At the same time,we also introduce Nb-TiOx thin films into the device as electron transport layer by low temperature pulsed laser deposition(PLD)method.PLD technology could not only fabricate Nb-TiOx electron transport layer,but also realize low temperature and flexible fabrication process of devices.It has very excellent application prospects.Based on the PLD technology,large area devices(225 mm2)with 11.5%photoelectric conversion efficiency and flexible devices with 12.5%photoelectric conversion efficiency were fabricated.This work has very important reference significance for the study of PSCs with high performance and environmental stability.(2)Secondly,in order to explore solutions to improve the optical stability of PSCs.We try to introduce a photon energy down-conversion layer inside the device to improve the ultraviolet(UV)stability of the device.PL photoluminescence spectra show that SrAl2O4:Eu2+,Dy3+can emit visible light at 520 nm after being stimulated by UV light.The PLD method is used to introduce SrAl2O4:Eu2+,Dy3+thin films with thickness of 200 nm into the PSCs device,which improves the UV stability and illumination stability of the device,and makes the photoelectric conversion efficiency of the device reach 17.8%.At the same time,due to the long afterglow effect of SrAl2O4:Eu2+,Dy3+materials,PSCs devices have the same afterglow current without illumination.This is the first time that PSCs devices with optical storage effect have been realized.(3)Thirdly,all-inorganic perovskite nanocrystals have the advantages of simple synthesis method,adjustable band gap and high fluorescence quantum efficiency.Their down-conversion effect on UV light makes them an effective photon energy conversion layer.In this work,CsPbBr3 nanocrystals were introduced into the structure of PSCs devices.The devices fabricated by vapor deposition and one-step solution method exhibited 16.4%and 20.8%photoelectric conversion efficiency,respectively,which were 11.6%and 5.6%higher than those without CsPbBr3 modification.The improvement of photoelectric conversion efficiency can be attributed to the effective utilization of UV light by PSCs and the suppression of carrier recombination at the interface of PSCs.At the same time,CsPbBr3 layer can also significantly improve the lightstability of the device,so that the stability time of the prepared PSCs device can still be maintained for more than 100 hours under sustained high-energy UV ultraviolet irradiation.In addition,CsPbBr3 modified devices have very low hysteresis effect and various fluorescent colors.In this work,photon energy down-conversion and carrier interface modification are realized simultaneously,which provides a research idea for the preparation of PSCs with high efficiency and light stability.(4)Further,we found that perovskite materials still have serious decomposition problems at higher temperatures.The decomposition of perovskite materials will directly cause the performance degradation of PSCs devices,which also seriously hinders the application process of PSCs under actual conditions.It is found that the crystallinity and structural stability of the films can be effectively improved when the precursor solution MA3Bi2Br9 containing Bi3+ions is added to FA0.83MA0.17Pb(I0.83Br0.17)3 perovskite precursor solution.The photoelectric conversion efficiency of PSCs doped with Bi3+can reach 19.4%.The improvement of device performance can be attributed to the reduction of lattice defects,the increase of grain size and the improvement of electronic extraction efficiency.More importantly,Bi3+doping could significantly improve the thermal stability of PSCs devices at 80-180?,and achieves a long-term stability of 2500 hours.It is attributed to the fact that Bi3+can increase the tolerance factor of perovskite materials,improve the phase stability and structural stability of crystals,and decrease the degradation rate of doped perovskite films at high temperature.In this work,by modifying the structure defect of perovskite photoactive layer,a simple way to prepare PSCs with high efficiency and thermal stability was realized.(5)Finally,we modified the electron transport layer and the hole transport layer in the device by rare earth ions and conjugated small molecules,and prepared the double-interface modified PSCs device.Firstly,the rare earth ion doped titanium dioxide prepared by low temperature electron beam evaporation process can show higher conductivity and more reasonable band gap matching,so that the optimized PSCs devices show 19.6%photoelectric conversion efficiency.In addition,high quality perovskite thin films can be prepared by introducing a small amount of DRCN5T into antisolvent chlorobenzene,which makes the photoelectric conversion efficiency of the devices up to 20.53%.The PSCs modified by two interfaces have very low hysteresis effect.Finally,we have fabricated flexible,large area and semi-transparent PSCs.The results show that this work provides a method to fabricate PSCs with high efficiency,high stability,flexibility,large area and translucency. |
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