ABSTRACT
Recently, lead halide perovskite nanocrystal (NC)-based heterostructures have demonstrated significant promise in various research areas, including solar cells, CO2 reduction, and photocatalysis. These hybrid structures have also played a crucial role in advancing our fundamental conception of charge transfer mechanisms occurring at the interface. A thin shell around the NCs is not suitable for the formation of stable and luminescent materials. However, such NCs are suitable for solar cells, LEDs, CO2 reduction, and photocatalytic applications due to higher carrier mobility. Thick-shelled NCs are highly stable but hinder charge transport among the NCs which is beneficial for bio-imaging and color-converted LED fabrication. So, understanding the mechanism of charge transport among the NCs dependent on the shell materials is important. Here, we synthesized CsPbBr3 NCs with various coating materials to vary the effective distance between the perovskite and nitrogen-doped carbon quantum dots (NCQDs) to understand the charge transfer process among them. We encapsulated the NCs with different coating materials (i.e., oleic acid, oleylamine, polyvinylpyrrolidone, and silica) such that the thickness of the NCs' shell can differ. We observed that the charge transfer rate between thick-shelled NCs and NCQDs is slow. The faster charge transfer among the thinner-shelled NCs and NCQDs is feasible due to the bonding of the N-state of NCQDs with Pb-atoms of the CsPbBr3 structure. The density functional theory (DFT) calculations of the heterostructure indicate that the electron acceptor state of the N-atom in NCQDs lies below the conduction band of perovskite NCs, which is accountable for such charge transfer. This study has immense significance as it provides crucial insights into the design and application of heterostructures, which can be extended to various novel opportunities for progress and innovation.
ABSTRACT
Formamidinium lead halide (FAPbX3) has attracted greater attention and is more prominent recently in photovoltaic devices due to its broad absorption and higher thermal stability in comparison to more popular methylammonium lead halide MAPbX3. Herein, a simple and highly reproducible room temperature synthesis of device grade high quality formamidinium lead bromide CH(NH2)2PbBr3 (FAPbBr3) colloidal nanocrystals (NC) having high photoluminescence quantum efficiency (PLQE) of 55-65% is reported. In addition, we demonstrate high brightness perovskite light emitting device (Pe-LED) with these FAPbBr3 perovskite NC thin film using 2,2',2â³-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) commonly known as TPBi and 4,6-Bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine (B3PYMPM) as electron transport layers (ETL). The Pe-LED device with B3PYMPM as ETL has bright electroluminescence of up to 2714 cd/m2, while the Pe-LED device with TPBi as ETL has higher peak luminous efficiency of 6.4 cd/A and peak luminous power efficiency of 5.7 lm/W. To our knowledge this is the first report on high brightness light emitting device based on CH(NH2)2PbBr3 widely known as FAPbBr3 nanocrystals in literature.
ABSTRACT
Recently, CsPbBr3 perovskites have been emerging as very promising green emission materials for light-emitting diodes (LEDs) due to their high color purity, low cost and high photoluminescence quantum yield (PLQY). However, the corresponding LED performance is still low and far behind CH3NH3PbBr3; it is due to the lack of proper perovskite film preparation methods and interfacial engineering. Herein, we report highly bright and durable CsPbBr3-based LEDs fabricated using a one-step solution method. The precursor solution is prepared by simply dissolving CsPbBr3 powder and a CsBr additive in dimethyl sulfoxide (DMSO). We find that the CsBr additive not only significantly enhances the PLQY but also induces directional crystal growth into micro-plates, forming a smooth perovskite film for LEDs. LEDs employing such high quality films show a high luminance of 7276 cd m-2 and high color purity with a full width at half maximum of 18 nm. Furthermore, the as-fabricated LEDs reveal an outstanding ambient stability with a decent luminance output (>100 cd m-2, steady increase without any degradation trend) for at least 15 h under a constant driving current density (66.7 mA cm-2). And we propose two reasons for this unique luminance increasing behavior: (1) the CsPbBr3 perovskite is thermally stable and can survive from joule heat; and (2) on the other hand, the joule heating will induce interface or crystalline film annealing, reduce device resistance and then enhance the luminance output.
ABSTRACT
Copper thiocyanate (CuSCN) is introduced as a hole-injection/hole-transport layer (HIL/HTL) for solution-processed organic light-emitting diodes (OLEDs). The OLED devices reported here with CuSCN as HIL/HTL perform significantly better than equivalent devices fabricated with a PEDOT:PSS HIL/HTL, and solution-processed, phosphorescent, small-molecule, green OLEDs with maximum luminance ≥10 000 cd m(-2) , maximum luminous efficiency ≤50 cd A(-1) , and maximum luminous power efficiency ≤55 lm W(-1) are demonstrated.
