In this paper, highly stable violet-blue emitting ZnSe/ZnS core/shell QDs have been synthesized by a novel "low temperature injection and high temperature growth" method. The resulting nearly monodisperse ZnSe/ZnS core/shell QDs exhibit excellent characteristics such as a high color saturation (typical spectral full width at half-maximum between 12 and 20 nm), good emission tunability in the violet-blue range of wavelengths from 400 to 455 nm, a high absolute PL quantum yield (up to 83%), and superior chemical and photochemical stability. By employing ZnSe/ZnS core/shell quantum dots (QDs) as emitters with a fully solution processable method, bright, efficient, and color-stable violet Cd-free quantum dot-based light-emitting diodes (QD-LEDs) with maximum luminance up to 2632 cd m(-2) and a peak EQE of 7.83% have been demonstrated successfully. Considering the factors of the photopic luminosity function, the brightness and efficiency results of such violet QD-LEDs not only represent a 12-fold increase in device efficiency and an extraordinary 100 times increase in luminance compared with previous Cd-free QD-LEDs but also can be much superior to the best performance (1.7%) of their Cd-based violet counterparts. These results demonstrate significant progress in short-wavelength QD-LEDs and shed light on the acceleration of commercial application of environmentally-friendly violet QD-based displays and lighting.

An ultrathin Mg(OH)2 layer was solution‐deposited onto the ZnO nanowires to solve the problem of interfacial charge recombination, caused by the increase of interfacial area in bulk heterojunction (BHJ) PbS colloidal quantum dot solar cells (CQDSCs). This Mg(OH)2 interlayer efficiently passivated the surface defects of ZnO nanowires and provided tunnel barrier at ZnO/PbS interface. As a result, the charge recombination at ZnO/PbS interface was largely suppressed, proved by the significantly elongated electron lifetime and the increased open‐circuit voltage of the Mg(OH)2‐involved BHJ CQDSCs. Careful thickness optimization of Mg(OH)2 interlayer finally brought a ∼33% increase in Voc and ∼25% improvement in power conversion efficiency.

Lead sulfide (PbS) colloidal quantum dot solar cells (CQDSCs) present the distinctive ability to utilize short-wave infrared light, good ambient stability, and convenient solution-based fabrication processes and thus attract much attention in the photovoltaic research field. The performance of CQDSCs has been improved by constructing the ZnO/PbS heterojunction, due to suitable band levels and electron mobility of ZnO electron transfer layer (ETL). However, the huge number of defects in low-temperature processed ZnO cause an unbalanced carrier-related processes, which restrict further performance enhancement and flexible production of CQDSCs. Here, we described a facile method to passivate defects in low-temperature sol–gel ZnO by introducing polyethylenimine (PEI) into the precursor solution. Versus the original ZnO film, the composite ZnO:PEI films exhibit better crystallization because of the Zn–N interaction. A series of electronic analyses have shown that the addition of PEI reduces the work function (WF) of ZnO and increases the built-in voltage (V bi) at the heterojunction interface, suggesting that the carrier separation is improved in the depletion region of solar cells. The carrier transport in ZnO ETL is also optimized by PEI, since the electron mobility of ZnO is maximized when the mass faction of PEI is 5%. In addition, the carrier recombination is effectively suppressed in the ZnO:PEI based solar cells proved by the increased carrier lifetime. Consequently, a power conversion efficiency (PCE) of 7.30% was achieved with the ZnO:PEI 5% film versus 5.84% for the reference cellthis was attributed to the optimized carrier-related processes.

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