Cesium lead halide (CsPbX) perovskite nanocrystals (NCs) have demonstrated extremely excellent optical properties and great application potentials in various optoelectronic devices. However, because of the anion exchange, it is difficult to achieve white-light and multicolor emission for practical applications. Herein, we present the successful doping of various lanthanide ions (Ce, Sm, Eu, Tb, Dy, Er, and Yb) into the lattices of CsPbCl perovskite NCs through a modified hot-injection method. For the lanthanide ions doped perovskite NCs, high photoluminescence quantum yield (QY) and stable and widely tunable multicolor emissions spanning from visible to near-infrared (NIR) regions are successfully obtained. This work indicates that the doped perovskite NCs will inherit most of the unique optical properties of lanthanide ions and deliver them to the perovskite NC host, thus endowing the family of perovskite materials with excellent optical, electric, or magnetic properties.

Quantum cutting can realize the emission of multiple near-infrared photons for each ultraviolet/visible photon absorbed, and has potential to significantly improve the photoelectric conversion efficiency (PCE) of solar cells. However, due to the lack of an ideal downconversion material, it has merely served as a principle in the laboratory until now. Here, the fabrication of a novel type of quantum cutting material, CsPbCl Br :Yb , Ce nanocrystals is presented. Benefiting from the larger absorption cross-section, weaker electron-phonon coupling, and higher inner luminescent quantum yield (146%), the doped perovskite nanocrystals are successfully explored as a downconverter of commercial silicon solar cells (SSCs). Noticeably, the PCE of the SSCs is improved from 18.1% to 21.5%, with a relative enhancement of 18.8%. This work exhibits a cheap, convenient, and effective way to enhance the PCE of SSCs, which may be commercially popularized in the future.

long carrier diffusion lengths, adjustable bandgaps, and low-cost fabrication. [1][2][3] Until now, the certified power conversion efficiency (PCE) has reached 25.5%, [4] making the PSC a promising candidate for the next-generation thin-film solar cells. [3,5] However, the presently obtained record PCE is still far from Shockley-Queisser limit efficiency. [6] In addition, the currently achieved stability is much lower below the standard of commercial application. It is well known that poor perovskite film quality is one of the main reasons for efficiency and stability losses. Consequently, it is highly expected to minimize the trap-assisted nonradiative recombination losses via improving perovskite film quality.The traditional solution method with fast crystallization and high-temperature annealing process would inevitably lead to a variety of defects in perovskite bulk and at the surfaces and grain boundaries (GBs). [7][8][9] Most defects in the bulk of perovskite films are shallow-level defects, while most defects at the surface and GBs of perovskite films are deep-level defects, which is detrimental to device performance through capturing carriers. [6,10,11] Moreover, these defects would provide pathways for ion migration, which results in efficiency and stability losses. [6,12,13] In addition, water and oxygen would preferentially attack the surface and GBs of perovskiteThe nonradiative recombination losses resulting from the trap states at the surface and grain boundaries directly hinder the further enhancement of power conversion efficiency (PCE) and stability of perovskite solar cells. Consequently, it is highly desirable to suppress nonradiative recombination through modulating perovskite crystallization and passivating the defects of perovskite films. Here, a simple and effective multifunctional additive engineering strategy is reported where 11 Maleimidoundecanoic acid (11MA) units with carbonyls (carboxyl and amide) and long hydrophobic alkyl chain are incorporated into a perovskite precursor solution. It is revealed that improved crystallinity, reduced trap state density, and inhibited ion migration are achieved, which is ascribed to the strong coordination interaction between the carbonyl groups at both sides of 11MA molecules and Pb 2+ . As a result, improved efficiency and stability are achieved simultaneously after introducing 11MA additive. The device with 11MA additive delivers a champion PCE of 23.34% with negligible hysteresis, which is significantly higher than the 18.24% of the control device. The modified device maintains around 91% of its initial PCE after aging under ambient conditions for 3000 h. This work provides a guide for developing multifunctional additive molecules for the purpose of simultaneous improvement of efficiency and stability.

Lead halide perovskite nanocrystals are currently under intense investigation as components of solution-processed light-emitting devices (LEDs). We demonstrate LEDs based on Ag doped–passivated CsPbI3 perovskite nanocrystals with external quantum efficiency of 11.2% and an improved stability. Ag and trilayer MoO3/Au/MoO3 structure were used as cathode and anode, respectively, which reduce the electron injection barrier and ensure the high transparency and low resistance of the anode. Silver ions diffuse into perovskite film from the Ag electrode, as confirmed by the elemental mapping, the presence of Ag 3d peaks in the X-ray photoelectron spectrum, and the peak shift in the X-ray diffraction patterns of CsPbI3. In addition to doping, silver ions play the beneficial role of passivating surface defect states of CsPbI3 nanocrystals, which results in increased photoluminescence quantum yield, elongated emission lifetime, and improved stability of perovskite films.

Carbon dots (CDs) have emerged as novel fluorescent probes due to their remarkable optical properties; however, red emission is still rare, has a relatively low efficiency, and its mechanism remains ambiguous. Herein, relatively efficient red-emission CDs based on p-phenylenediamine were prepared through various solvothermal means, where the highest quantum yield approached 41.1% in n-amyl alcohol, which was the most efficient quantum yield reported to date. Various structural characterizations were performed and confirmed that the red emission originated from the molecular states consisting of a nitrogen-containing organic fluorophore. The CDs were dispersed in different organic solvents and showed tunable emission, evolving from green to orange-red in aprotic solvents and a red emission in protic solvents. Further solvent correlation studies indicated that the hydrogen bond effect between the CDs and solvents was the main mechanism leading to the spectral shift. Accordingly, solid-state luminescent CDs-polymers were fabricated, which also demonstrated continuously tunable emission properties. This work opens a new window for recognizing the generation of tunable and red-emission CDs.

A 2D surface plasmon photonic crystal (SPPC) is achieved by implanting gold nanorods onto the periodic surface apertures of the poly(methyl methacrylate) (PMMA) opal photonic crystals. On the surface of the SPPC, the overall upconversion luminescence intensity of NaYF4 :Yb(3+) , Er(3+) under 980 nm excitation is improved more than 10(3) fold. The device is easily shifted to a transparent flexible substrate, applied to flexible displays.

Here we present the synthesis of core-shell structured hexagonal-phase NaYF 4 : Yb 3+ ,Er 3+ @Ag nanoparticles (NPs) and their unique bio-functional properties. The structure and morphology of the NPs are confirmed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) measurements. They displayed both strong 2 H 11/2 / 4 S 3/2 -4 I 15/2 (green) and 4 F 9/2 -4 I 15/2 (red) upconversion luminescence (UCL) and photothermal transfer properties under the excitation of a continuous 980 nm laser diode. Furthermore, the UCL intensity ratio of 2 H 11/2 -4 I 15/2 to 4 S 3/2 -4 I 15/2 acted as a temperature sensor due to the low energy gap between 2 H 11/2 and 4 S 3/2 ($740 cm À1 ). After coating with the silver shell, the cytotoxicity of the composite NPs was reduced largely in contrast to the pure NaYF 4 : Yb 3+ ,Er 3+ NPs. HepG2 cells from human hepatic cancer and BCap-37 cells from human breast cancer incubated with the composite NPs in vitro were found to undergo photothermally induced death on exposure to 980 nm NIR light, and the optimum mortality approaches 95% with a power density of 1.5 W cm À2 which is much lower than that reported for Au nanoshells and Au nanorods. Overall, this class of core/shell NPs is expected to be an attractive therapeutic agent for tumor ablation with bioimaging and thermal detection in real time.

Recently, various lanthanide ions (Ln 3+ ) have been successfully doped into perovskite quantum dots (PQDs), and the quantum-cutting emission of 2 F 5/2 − 2 F 7/2 for Yb 3+ with a measurable inner efficiency of more than 100% has been discovered and applied as the luminescent converter of solar cells, which has opened a new branch for the application of PQDs. In this work, to further improve the quantum-cutting efficiency of Yb 3+ , the codoping and tridoping methods were used to improve the quantum-cutting emission of PQDs. The Yb 3+ −Ln 3+ (Ln = Nd, Dy, Tb, Pr, Ce) pair-doped CsPbCl x Br y I 3−x−y PQDs were fabricated, with all displaying excitonic emission, narrowband emission of Ln 3+ ions, and quantum-cutting emission of Yb 3+ ions. It was interesting that Yb 3+ −Pr 3+ as well as Yb 3+ −Ce 3+ pairs could effectively sensitize the emission of Yb 3+ , owing to Pr 3+ and Ce 3+ ions offering intermediate energy states close to the exciton transition energy of the PQDs. After host composition optimization and tridoping investigation, overall emissions with a 173% photoluminescence quantum yield (PLQY) were obtained in the Yb 3+ −Pr 3+ −Ce 3+ -tridoped CsPbClBr 2 PQDs. Then, the tridoped PQDs were designed as the down-converter for CuIn 1−x Ga x Se 2 (CIGS) as well as the silicon solar cells, which leads to an enhancement of the power conversion efficiency (PCE) of as high as ∼20%. The modified CIGS was further employed to charge the smart mobile phone, which could largely shorten the charging time from 180 to 150 min. This finding is of great significant for expanding the application fields of the impurity-doped PQDs.