Structure optimization of perovskite quantum dot light-emitting diodes.

Although all-inorganic perovskite light emitting diodes (PeLED) have satisfactory stability under an ambient atmosphere, producing devices with high performance is challenging. A device architecture with a reduced energy barrier between adjacent layers and optimized energy level alignment in the PeLED is critical to achieve high electroluminescence efficiency. In this study, we report the optimization of a CsPbBr3-based PeLED device structure with Li-doped TiO2 nanoparticles as the electron transport layer (ETL). Optimal Li doping balances charge carrier injection between the hole transport layer (HTL) and ETL, leading to superior performance in both devices. The turn-on voltages for devices with Li-doped TiO2 nanoparticles were significantly reduced from 7.7 V to 4.9 V and from 3 V to 2 V in the direct and inverted PeLED structures, respectively. The low turn-on voltage for green emission is one of the lowest values among the reported CsPbBr3-based PeLEDs. Further investigations show that the device with an inverted structure is superior to the device with a direct structure because the energy barrier for carrier injection was minimized. The inverted structure devices exhibited a current efficiency of 5.6 cd A-1 for the pristine TiO2 ETL, while it was 15.2 cd A-1 for the Li-doped TiO2 ETL, a factor of ∼2.7 enhancement at 5000 cd m-2.

A Color Tunable Quantum-Dot Light-Emitting Diode Device Driven by Variable Voltage.

A hole transporting layer (HTL) consisting of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine)] doped with 4,4'-Bis(9H-carbazol-9-yl)biphenyl was designed for high-performance multicolor quantum-dot light-emitting diode (QLED) fabricated by an all-solution process technique. The band structure of the HTL is tailored via small molecule doping to create a cascade of highest occupied molecular orbital levels (HOMO) from the hole injection layer to the quantum-dot emissive layer (EML). This energy band tailoring significantly overcomes the energy barrier for hole injection and enables multicolor emission from a single device, which consists of mixture of red, green, and blue QDs as EML. The color tunability as a function of applied voltage is the most novel feature of our device. The color tunability was observed at a voltage of 2 V for red emission, 3 V for orange, 4 V for yellow and 6 V for greenish white and a high brightness of 15,000 cd m-2 was demonstrated for white emission, which is attributed to the efficient and balanced carriers' injection into the EML. The strategy of using tunable HOMO of the HTL in combination with color tunability of the EML as a function of applied voltage, pushes QLED a step closer to practical multicolor display applications.

Interfacial Energy-Level Alignment for High-Performance All-Inorganic Perovskite CsPbBr3 Quantum Dot-Based Inverted Light-Emitting Diodes.

All-inorganic perovskite light-emitting diode (PeLED) has a high stability in ambient atmosphere, but it is a big challenge to achieve high performance of the device. Basically, device design, control of energy-level alignment, and reducing the energy barrier between adjacent layers in the architecture of PeLED are important factors to achieve high efficiency. In this study, we report a CsPbBr3-based PeLED with an inverted architecture using lithium-doped TiO2 nanoparticles as the electron transport layer (ETL). The optimal lithium doping balances the charge carrier injection between the hole transport layer and ETL, leading to superior device performance. The device exhibits a current efficiency of 3 cd A-1, a luminance efficiency of 2210 cd m-2, and a low turn-on voltage of 2.3 V. The turn-on voltage is one of the lowest values among reported CsPbBr3-based PeLEDs. A 7-fold increase in device efficiencies has been obtained for lithium-doped TiO2 compared to that for undoped TiO2-based devices.

Effects of TiCl4 Post-Treatment on the Efficiency of Dye-Sensitized Solar Cells.

The effects of compact TiO2 overlayers, deposited on TiO2 photoelectrodes through the hydrolysis of TiCl4, on the overall performance of dye-sensitized solar cells (DSSCs) were investigated. A thermal treatment at high-enough temperature was required for a more effective and higher dye-loading of the compact TiO2 overlayers. This led to improvements in the crystallinity and porosity of the layer, which contributed to higher power conversion efficiencies (PCE) of DSSCs compared with the electrodes prepared at relatively lower temperatures. Moreover, the existence of an additional secondary overlayer led to an increase in the net PCE of the cells by increasing the amount of dye-loading, even though this layer itself, in the absence of a first overlayer formed under high thermal treatment, did not enhance cell efficiency, because of the higher charge transport resistance over the layers and an increase in surface states.

Development of eSSR-Markers in Setaria italica and Their Applicability in Studying Genetic Diversity, Cross-Transferability and Comparative Mapping in Millet and Non-Millet Species.

Foxtail millet (Setariaitalica L.) is a tractable experimental model crop for studying functional genomics of millets and bioenergy grasses. But the limited availability of genomic resources, particularly expressed sequence-based genic markers is significantly impeding its genetic improvement. Considering this, we attempted to develop EST-derived-SSR (eSSR) markers and utilize them in germplasm characterization, cross-genera transferability and in silico comparative mapping. From 66,027 foxtail millet EST sequences 24,828 non-redundant ESTs were deduced, representing ~16 Mb, which revealed 534 (~2%) eSSRs in 495 SSR containing ESTs at a frequency of 1/30 kb. A total of 447 pp were successfully designed, of which 327 were mapped physically onto nine chromosomes. About 106 selected primer pairs representing the foxtail millet genome showed high-level of cross-genera amplification at an average of ~88% in eight millets and four non-millet species. Broad range of genetic diversity (0.02-0.65) obtained in constructed phylogenetic tree using 40 eSSR markers demonstrated its utility in germplasm characterizations and phylogenetics. Comparative mapping of physically mapped eSSR markers showed considerable proportion of sequence-based orthology and syntenic relationship between foxtail millet chromosomes and sorghum (~68%), maize (~61%) and rice (~42%) chromosomes. Synteny analysis of eSSRs of foxtail millet, rice, maize and sorghum suggested the nested chromosome fusion frequently observed in grass genomes. Thus, for the first time we had generated large-scale eSSR markers in foxtail millet and demonstrated their utility in germplasm characterization, transferability, phylogenetics and comparative mapping studies in millets and bioenergy grass species.