All Inorganic Mixed Halide Perovskite Nanocrystal-Graphene Hybrid Photodetector: From Ultrahigh Gain to Photostability.

Hybrid graphene-perovskite photodetectors embrace the excellent photoabsorption properties of perovskites and high carrier mobility of graphene in a single device. Here, we demonstrate the integration of halide-ion-exchanged CsPbBrI nanocrystals (NCs) as a photoabsorber and graphene as a transport layer. The NCs conform to a cubic lattice structure and exhibit an optical band gap of 1.

Stable Sn doped FAPbI nanocrystals for near-infrared LEDs.

Herein, we report Sn2+ doping in FAPbI3 NCs to stabilize the α-phase, while using propionic acid as a co-ligand. The Sn2+ doping enhances the emission quantum yield from 35% to 63% and dramatically improves the colloidal and phase stability. Also, we demonstrated the use of Sn doped FAPbI3 NCs in near-infrared (NIR) LEDs.

Low threshold and efficient multiple exciton generation in halide perovskite nanocrystals.

Multiple exciton generation (MEG) or carrier multiplication, a process that spawns two or more electron-hole pairs from an absorbed high-energy photon (larger than two times bandgap energy E), is a promising way to augment the photocurrent and overcome the Shockley-Queisser limit. Conventional semiconductor nanocrystals, the forerunners, face severe challenges from fast hot-carrier cooling. Perovskite nanocrystals possess an intrinsic phonon bottleneck that prolongs slow hot-carrier cooling, transcending these limitations.

Inducing Isotropic Growth in Multidimensional Cesium Lead Halide Perovskite Nanocrystals.

A new two-step synthetic protocol to yield monodisperse spherical zero-dimensional (0D) Cs PbX nanocrystals (NCs) and three-dimensional (3D) CsPbX NCs is described. The first step of the reaction involves the colloidal synthesis of spherical PbX seed NCs, which are subsequently converted to Cs PbX and CsPbX NCs through hot injection of a Cs precursor at the desired reaction temperatures. By employing less reactive Pb and halide precursors, the reaction time was extended from several seconds to about five minutes, thereby allowing greater control during the crystallization and growth stages.

Facile Method to Reduce Surface Defects and Trap Densities in Perovskite Photovoltaics.

Owing to improvements in film morphology, crystallization process optimization, and compositional design, the power conversion efficiency of perovskite solar cells has increased from 3.8 to 22.1% in a period of 5 years.

An Interactive Quantum Dot and Carbon Dot Conjugate for pH-Sensitive and Ratiometric Cu Sensing.

Herein we report the photoinduced electron transfer from Mn -doped ZnS quantum dots (Qdots) to carbon dots (Cdots) in an aqueous dispersion. We also report that the electron transfer was observed for low pH values, at which the oppositely charged nanoparticles (NPs) interacted with each other. Conversely, at higher pH values the NPs were both negatively charged and thus not in contact with each other, so the electron transfer was absent.

Engineering Interfacial Charge Transfer in CsPbBr Perovskite Nanocrystals by Heterovalent Doping.

Since compelling device efficiencies of perovskite solar cells have been achieved, investigative efforts have turned to understand other key challenges in these systems, such as engineering interfacial energy-level alignment and charge transfer (CT). However, these types of studies on perovskite thin-film devices are impeded by the morphological and compositional heterogeneity of the films and their ill-defined surfaces. Here, we use well-defined ligand-protected perovskite nanocrystals (NCs) as model systems to elucidate the role of heterovalent doping on charge-carrier dynamics and energy level alignment at the interface of perovskite NCs with molecular acceptors.

Redox-Tuned Three-Color Emission in Double (Mn and Cu) Doped Zinc Sulfide Quantum Dots.

The photoluminescence characteristics of colloidal Mn(2+) and Cu(2+) (double) doped zinc sulfide (ZnS) quantum dots (Qdots) could be drastically influenced by reactions with redox reagents. Importantly, experiments revealed Cu(+) in ZnS nanocrystals rather than Cu(2+), in conjunction with Mn(2+), as the emitting dopant. Thus, as-synthesized aqueous Qdots emitted orange (with peaks at 460 and 592 nm) due to the host and Mn(2+) dopant emissions.

Recovering hidden quanta of Cu(2+)-doped ZnS quantum dots in reductive environment.

We report that photoluminescence of doped quantum dots (Qdots)-which was otherwise lost in the oxidized form of the dopant-could be recovered in chemical or cellular reducing environment. For example, as-synthesized Cu(2+)-doped zinc sulfide (ZnS) Qdots in water medium showed weak emission with a peak at 420 nm, following excitation with UV light (320 nm). However, addition of reducing agent led to the appearance of green emission with a peak at 540 nm and with quantum yield as high as 10%, in addition to the weak peak now appearing as a shoulder.

Surface ion engineering of Mn2+-doped ZnS quantum dots using ion-exchange resins.

We report the engineering of surface ions present as defects in doped quantum dots (Qdots) following their synthesis. This was achieved by treating the Qdots with cation-exchange resin beads (CB). An aqueous dispersion of Mn(2+)-doped ZnS Qdots, when treated with different amounts of CB, resulted in two kinds of changes in the emission due to Mn(2+) ions.

In situ reversible tuning of photoluminescence of Mn2+-doped ZnS quantum dots by redox chemistry.

Herein we report the development of a new method for in situ reversible tuning of photoluminescence properties of quantum dots (Qdots) by partial oxidation of population of the emitting species and subsequent chemical reduction of the oxidized form. The concept has been demonstrated using Mn(2+)-doped ZnS Qdots stabilized by acetyl acetonate. Treatment of an aqueous solution of the Qdots (with Mn(OAc)(2) being the source of Mn used for the synthesis of the Qdots) by potassium peroxodisulfate (KPS) led to reduction of intensity of emission due to Mn(2+) ((4)T(1)-(6)A(1)).