Preparation And Properties Of CsPbBr₃ All-Inorganic Perovskite Light-Emitting Diodes

Perovskite materials are used extensively in the field of light-emitting diodes,owing to its distinctive optical and electrical characteristics,such as tunable bandgap,high color purity and solution-processability at low temperature,a best external quantum efficiency over 20%has been achieved in perovskite light-emitting diodes(PeLEDs).Compared with its organic-inorganic counterparts,all-inorganic perovskites show better stability under ambient condition,however,the all-inorganic perovskite films suffer poor surface coverage as well as low electroluminescence(EL)efficiency,which is one of the key issues that impedes rapid commercialization.In this thesis,the device performance has been improved significantly by:1)adding a highly soluble polymer into the perovskite precursor thus passivating the perovskite film and 2)optimizing the technology of the two-step spin-coating method.The main works of this thesis are listed as follows:(1)A highly soluble polymer at room temperature:methoxypolyethylene glycol(mPEG)was added into the perovskite precursor,the as fabricated perovskite film using one-step spin-coating method show decreased grain size as well as improved surface morphology.The results show that by modifying the concentration of mPEG,the perovskite grain size decreased significantly from 151 nm to 93 nm,the fluorescence lifetime increased from 13.79 ns to 55.86 ns,as well as better crystallinity.The fabricated PeLED shows a maximum luminance of 33500 cd m-2 and a maximum current efficiency of 3.14 cd A-1.Meantime,the luminescence at 2 V,which is lower than its bandgap voltage,has been detected in general device structure for the first time.The PeLED also shows good stability,maintain its initial luminance of 100 cd m-2 for more than 24 h after encapsulation.(2)A simplest two-step spin-coated method,to spin-coat PbBr2 and CsBr solution in sequence,is employed,and the dipping or loading time is not needed to make full reaction.By modifying the thickness of PbBr2 film,the concentration of CsBr and the final annealing time,high quality perovskite film could be achieved.The results show that the grain size decrease from 114 nm to 67 nm,and the surface coverage is notably increased,which are beneficial for reducing non-radiative processes,a maximum luminance and a current efficiency of 16106 cd m-2 and 1.68 cd A-1 have been achieved,respectively,which are not only far better than previous two-step fabricated all-inorganic PeLEDs,but as efficient as one-step ones(without any additives and post-treatment),indicating good prospect of the two-step fabricated all-inorganic PeLEDs.