The Research On Highly Efficient And Stable Perovskite LEDs

Metal halide perovskite materials have drawn a high level of research interest in the past decades due to their superior electrical and optical properties,such as strong optical absorption,tunable band gaps,low non-radiative recombination rates,relatively high charge-carrier mobility and long diffusion lengths.So far,perovskite solar cells have demonstrated a high power conversion efficiency of 22.7%,which is outperforming conventional polycrystalline silicon solar cells.In addition to their use in photovoltaics,perovskites are promising for realizing light-emitting diodes(LEDs)owing to their facile solution processing,high color purity with narrow emission linewidths less than 20 nm and high photoluminescence quantum yield(PLQY,greater than 90%in solution for nanocrystals).In this thesis,we focused on the preparation of the perovskite films and devices.We obtained thin perovskite films with high quality by one-step method and further explored the ideal preparation process of assembling the devices by using them as emitting layer in order to achieve high-efficiency perovskite LEDs(PeLEDs).What's more,we explored the origins of the low stability of PeLEDs,which were manufactured in different preparation conditions,and employed two effective strategies to improve the stability of PeLEDs.The main experimental results were as follows:1.Preparation of perovskite emitting,charge injecting layer and manufacture perovskite light-emitting diodes.At first,we prepared three-dimensional(3D)perovskite Cs1-xMAxPbBr3 films and used them as emitting layer,ZnO or ZnMgO as electron injection layer and CBP as hole injection layer to manufacture three-dimensional perovskite based LEDs.Then larger-group ammonium halides compound was added to the perovskite precursor solution as a surfactant that dramatically constrained the growth of 3D perovskite grains during film formation,producing crystallites with small grain sizes and film roughness of less than 1 nm,namely quasi two-dimensional perovskite films.In order to manufacture quasi 2D perovskite based LEDs,we chose PEDOT:PSS as hole injection layer,quasi 2D perovskite films mentioned above as emitting layer and TBPi plays the important role in injecting electron.At last,we prepared two kinds of perovskite LEDs.2.Optimization of the preparation process of two kinds of perovskite LEDs for high efficiency.In 3D perovskite based LEDs,a series of devices with different thickness of CBP,Csi-xMAxPbBr3 and ZnMgO were prepared to balance the transport and injection of electron and hole.Through this way,we acquired high performance device.On the other hand,the electron injecting layer of ZnO was replaced by ZnMgO due to its well-matched energy level with the emitting layer,which can efficiently solve the large barrier for charge injection between ZnO and perovskite emitting layer.Furthermore,through electron-injecting interface passivation by PVP,high quality perovskite light-emitting thin films with minimized pinholes were obtained.This strategy was able to reduce the leakage current of our devices,as a result,the brightness and current efficiency of the LEDs were improved to 26000 cd/m2 and 8.67 cd/A.In quasi-2D perovskite based LEDs,various solutions concerning electron injection layer,hole injection layer,light-emitting layer and interface between them were developed to improve the performance of light-emitting diodes.The charge injection barrier between PEDOT:PSS and light-emitting layer can be reduced by adding PSS-Na into PEDOT:PSS aqueous solution.The valance band maximum of modified PEDOT:PSS was decreased by 0.2 eV,facilitating the hole injection and resulting in a higher efficiency.Then,the thickness of TBPi and LiF was optimized to improve the performance of devices.The influence of perovskite film thickness,annealing and component on the efficiency of the device was discussed in detail,later.We obtain highly efficient quasi-2D perovskite based light-emitting diodes with the current efficiency of 60.2 cd/A and external quantum efficiency of 18.5%,while n = 5 composition was used as the emitting material because of appropriate charge limited effect and better injection.In addition,PVP was also introduce to passivate the defective states,which generally acted as non-radiative recombination centers at the interfaces.3.Research on stability of PeLEDs.First,we compared the stability of PeLEDs PeLEDs.Then we found two effective strategies that wefabricated under different conditions and analyzed origins of the low stability of re AI2O3 intercalation and PVK doping to improve the stability of PeLEDs.The results showed that the devices lasted more lasted more than two hours when Al2O3 was introduced into our samples.