Benefited from excellent optical and electronic properties, metal halide perovskites are considered as good candidates for next generation semiconductors which have been widely investigated in many fields such as photodetectors (PDs), solar cells (SCs) and light emitting diodes (LEDs). In particular, features including bandgap tunability, high carrier mobility, defect tolerance ability as well as high photo luminance quantum yield (PLQY) in theory show more straightforward and significant optimization on light emission application. Low-dimensional perovskite, represented by quasi-2D perovskite and nanometer-sized nanoparticles is a good solution to prepare high performance perovskite-based LEDs (PeLEDs) by improving PLQY via quantum confinement, accelerating charge injection and enhance...[ Read more ]

Benefited from excellent optical and electronic properties, metal halide perovskites are considered as good candidates for next generation semiconductors which have been widely investigated in many fields such as photodetectors (PDs), solar cells (SCs) and light emitting diodes (LEDs). In particular, features including bandgap tunability, high carrier mobility, defect tolerance ability as well as high photo luminance quantum yield (PLQY) in theory show more straightforward and significant optimization on light emission application. Low-dimensional perovskite, represented by quasi-2D perovskite and nanometer-sized nanoparticles is a good solution to prepare high performance perovskite-based LEDs (PeLEDs) by improving PLQY via quantum confinement, accelerating charge injection and enhance exciton binding. Although the external quantum efficiency (EQE) of green, red and infrared PeLEDs have surpassed the 20% efficiency mark, approaching those of conventional inorganic and organic light-emitting diodes, the EQE of blue PeLEDs still fall behind. Besides, color-stability issue induced by ion-migration in mixed halide perovskites, scalability limited by conventional spin-coating method as well as short device lifetime inhibit further development of PeLEDs. Moreover, the effect of defects and surface / interface passivation and their influence on the performance of PeLEDs are still not clear.

As for the first work in this thesis, for the first time, we discovered a universal method to prepare organic-inorganic hybrid (BA)₂Cs_n−1Pb_nBr_3n+1 quasi-2D perovskite thin film by thermal evaporation method. By varying the material composition, annealing temperature, and film thicknesses, the crystal phase of the perovskite may be changed from 3D to 2D, controllably. Besides, the perovskite shows preferential growth along [100] zone axis suggested by 2D perovskite slabs so that carriers are confined inside 3D interlayers and the PLQY is enhanced as well. Importantly, we sandwich charge injection layer with anode and cathode on perovskite thin film to further prove the feasibility of all-evaporation fabrication of PeLEDs. As a result, a record high external quantum efficiency (EQE) of 5.3 percent was attained. In addition, a centimeter-scale PeLEDs (1.5 cm× 2 cm) has been obtained. Furthermore, with a thin layer PMMA passivation, the T₅₀ lifetime of our device with an initial brightness of 100 cd m^-2 is determined to be 90 minutes, which is among the longest for all PeLEDs fabricated via PVD method. Overall, our study provides a strong foundation for the high-performance PeLEDs with good reproducibility and large-scale production.

In second work, we discovered a lithography-free nano porous anodized aluminum oxide membranes (AAO) template with size quantization along radial direction. Then, a template-assisted low-pressure close space sublimation (CSS) process was presented to build three-dimensional (3D) all-inorganic perovskite quantum wire arrays (QPNWs) without any particular design. Benefit from quantum confinement and light extraction structure of AAO, high-density and good-uniformity 3D all-inorganic CsPbBr₃ QPNWs with high crystal quality, narrow full width at half-maximum (FWHM) PL peaks, high PLQY (~88%), and high OCE (exceeding 50%) are achieved using this unique template. Furthermore, a Poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB) hole-injection layer followed by top transparent electrode are deposited on top of QPNWs. We further replace TFB by a dual-functional small semiconductor molecule 1,1-Bis[(di-4-tolylamino) phenyl] cyclohexane (TAPC), which served as both passivation layer and hole-transporting layer, to improve device performance significantly. Eventually, our top light-emission PeLEDs show a maximum EQE of 11.8%, which are competitive in green-emission PeLEDs. These evidence points to a potential technique for implementing LD perovskite-based optoelectronics in real-world applications.

In the third part of work, we further extended the second part of work: to prepare AAO template with pore size smaller than 6 nm by coating certain thickness of aluminum oxide by ALD. Afterwards, CsPbBr₃ perovskite is filled inside to obtain monocrystalline ultra-small diameter CsPbBr₃ QPNW arrays (CsPbBr₃ s-QPNWs). The structural and photophysical properties of CsPbBr₃ s-QPNWs are characterized and discussed. As a result, the PL color can be tuned from green (512 nm) to cyan (492 nm) to sky-blue (481 nm) and finally to pure blue (467 nm), continuously. The PL color tunability via quantum size effects without halide doping exhibit good long-life stability and color stability. To better understand the photophysical properties of s-QPNWs, carrier dynamics and the influence of AAO passivation are studied and discussed. Eventually, PeLEDs with cyan, sky-blue and pure blue emission base on different diameters of CsPbBr₃ s-QPNWs are fabricated with maximum EQE of 7.1%, 3.2% and 0.9%, which are the best of pure CsPbBr₃ blue emission PeLEDs to our best knowledge.