IntroductionColloidal quantum dots (CQDs) offer advantages over conventional bulk inorganic semiconductors such as solution Low-temperature solution-processed high-effi ciency colloidal quantum dot (CQD) photovoltaic devices are developed by improving the interfacial properties of p-n heterojunctions. A unique conjugated polyelectrolyte, WPF-6-oxy-F, is used as an interface modifi cation layer for ZnO/PbS-CQD heterojunctions. With the insertion of this interlayer, the device performance is dramatically improved. The origins of this improvement are determined and it is found that the multifunctionality of the WPF-6-oxy-F interlayer offers the following essential benefi ts for the improved CQD/ZnO junctions: (i) the dipole induced by the ionic substituents enhances the quasi-Fermi level separation at the heterojunction through favorable energy band-bending, (ii) the ethylene oxide groups containing side chains can effectively passivate the interfacial defect sites of the heterojunction, and (iii) these effects occur without deterioration in the intrinsic depletion region or the series resistance of the device. All of the fi gures-of-merit of the devices are improved as a result of the enhanced built-in potential (electric fi eld) and the reduced interfacial charge recombination at the heterojunction. The benefi ts due to the WPF-6-oxy-F interlayer are generally applicable to various types of PbS/ZnO heterojunctions. Finally, CQD photovoltaic devices with a power conversion effi ciency of 9% are achievable, even by a solution process at room temperature in an air atmosphere. The work suggests a useful strategy to improve the interfacial properties of p-n heterojunctions by using polymeric interlayers.

The optical properties of ZnS–AgIn5S8 quantum dots (QDs) with core/shell structures are examined to clarify the enhancement mechanism of the photoluminescence (PL) quantum yield (QY). Two types of QDs are synthesized by varying the concentration of zinc precursors, with alloyed-core (ZnS–AgIn5S8, ZAIS), inner-shell (ZnIn2S4, ZIS), and outer-shell (ZnS) structures, such as ZAIS/ZIS/ZnS and ZAIS/ZnS. Upon alloying/shelling processes from the preformed AgIn5S8 QDs, the evolution of the band gap energy indicates the formation of the solid solution of ZAIS. Due to the difference in the degree of alloying between ZAIS/ZIS/ZnS and ZAIS/ZnS QDs, the blue shift of PL, Stokes shift, and QY are different. The alloying/shelling processes improve the QY of the intrinsic defect states more effectively than the QY of the surface defect states, while the time-resolved studies suggest that the enhanced radiative rate of the intrinsic states is responsible for the improvement of the QY, in addition to the reduced nonradiative rate. In ZAIS/ZIS/ZnS QDs, the QY increases to 85%, which is attributed to the existence of the ZIS layer, as well as the reduced nonradiative states and the enhanced radiative states by the alloying/shelling processes. The ZIS layer mitigates the lattice strains and provides the appropriate levels of the electronic structures in the QDs, which further reduces the nonradiative rate and enhances the radiative rate, respectively, leading to the unprecedentedly high PL QY of ZAIS/ZIS/ZnS QDs.

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Currently, heavy-shelled and gradient-shelled InP/ZnSeS/ZnS quantum dots (QDs) are commercially utilized as green (G) and red (R) color-converting layers in color-by-blue (B) QD-based displays. There is still a lack of systematic approaches to solve optical issues created when transforming QD nanoparticles into QD films. Here, triply protected approaches, such as using an Al dopant to passivate shell defects, Hf-nbutoxide (Hf(OtBu) 4 )-complex treatment to reduce ligand detachment, and the Al tri-sec-butoxide (Al(OsBu) 3 ) electrospray (E-spray) process to form an outer protecting layer and transform the material into QD-embedded Al 2 O 3 microbeads, are sequentially performed to improve the photoluminescence quantum yield (PLQY) and environmental stability of QDs. Moreover, QDembedded microbeads improve QD distribution uniformity inside Al 2 O 3 microbeads for high loading of nonagglomerated QDs and promote a scattering effect of QD green emission and blue excitation light in color-by-blue QD films. Therefore, the luminous efficacy (LE) of a mixed norland optical adhesive (NOA) film of QD@Al&Hf nanoparticles and QD@Al&Hf microbeads reaches ∼145.2 lm/W, which is 2.86 times higher than that of a QD@Al&Hf nanoparticle-only NOA film (50.8 lm/W). This combined approach can provide one example of promising combined approaches to fabrication of QD composite structures and suitable shapes for highly efficient and stable InP/ZnSeS/ZnS QD films in color-by-blue QD displays.