The Influence of Oxygen Plasma on Methylammonium Lead Iodide (MAPbI3) Film Doped with Lead Cesium Triiodide (CsPbI3)

In recent years, the study of organic–inorganic halide perovskite as an optoelectronics material has been a significant line of research, and the power conversion efficiency of solar cells based on these materials has reached 25.5%. However, defects on the surface of the film are still a problem to be solved, and oxygen plasma is one of the ways to passivate surface defects. In order to avoid destroying the methylammonium lead iodide (MAPbI₃), the influence of plasma powers on film was investigated and the cesium triiodide (CsPbI₃) quantum dots (QDs) were doped into the film. In addition, it was found that oxygen plasma can enhance the mobility and carrier concentration of the MAPbI₃ film.     

In Situ Ligand Bonding Management of CsPbI3 Perovskite Quantum Dots Enables High-Performance Photovoltaics and Red Light-Emitting Diodes

To fine-tune surface ligands towards high-performance devices, we developed an in situ passivation process for all-inorganic cesium lead iodide (CsPbI₃) perovskite quantum dots (QDs) by using a bifunctional ligand, L-phenylalanine (L-PHE). Through the addition of this ligand into the precursor solution during synthesis, the in situ treated CsPbI₃ QDs display significantly reduced surface states, increased vacancy formation energy, higher photoluminescence quantum yields, and much improved stability. Consequently, the L-PHE passivated CsPbI₃ QDs enabled the realization of QD solar cells with an optimal efficiency of 14.62 % and red light-emitting diodes (LEDs) with a highest external quantum efficiency (EQE) of 10.21 %, respectively, demonstrating the great potential of ligand bonding management in improving the optoelectronic properties of solution-processed perovskite QDs.     

Investigation of the Stability of Methylammonium Lead Iodide (MAPbI3) Film Doped with Lead Cesium Triiodide (CsPbI3) Quantum Dots under an Oxygen Plasma Atmosphere

In this study, we describe composited perovskite films based on the doping of lead cesium triiodide (CsPbI₃) quantum dots (QDs) into methylammonium lead iodide (MAPbI₃). CsPbI₃ QDs and MAPbI₃ were prepared by ligand-assisted re-precipitation and solution mixing, respectively. These films were optimized by oxygen plasma treatment, and the effect of powers from 0 to 80 W on the structural properties of the composited perovskite films is discussed. The experimental results showed that the light-harvesting ability of the films was enhanced at 20 W. The formation of the metastable state (lead(II) oxide and lead tetroxide) was demonstrated by peak differentiation-imitating. A low power enhanced the quality of the films due to the removal of organic impurities, whereas a high power caused surface damage in the films owing to the severe degradation of MAPbI₃.     

1D Choline-PbI3-Based Heterostructure Boosts Efficiency and Stability of CsPbI3 Perovskite Solar Cells

Defects in perovskite are key factors in limiting the photovoltaic performance and stability of perovskite solar cells (PSCs). Generally, choline halide (ChX) can effectively passivate defects by binding with charged point defects of perovskite. However, we verified that ChI can react with CsPbI₃ to form a novel crystal phase of one-dimensional (1D) ChPbI₃, which constructs 1D/3D heterostructure with 3D CsPbI₃, passivating the defects of CsPbI₃ more effectively and then resulting in significantly improved photoluminescence lifetime from 20.2 ns to 49.4 ns. Moreover, the outstanding chemical inertness of 1D ChPbI₃ and the repair of undesired δ-CsPbI₃ deficiency during its formation process can significantly enhance the stability of CsPbI₃ film. Benefiting from 1D/3D heterostructure, CsPbI₃ carbon-based PSCs (C-PSCs) delivered a champion efficiency of 18.05 % and a new certified record of 17.8 % in hole transport material (HTM)-free inorganic C-PSCs.     

Ambient Air Temperature Assisted Crystallization for Inorganic CsPbI2Br Perovskite Solar Cells

Inorganic cesium lead halide perovskites, as alternative light absorbers for organic–inorganic hybrid perovskite solar cells, have attracted more and more attention due to their superb thermal stability for photovoltaic applications. However, the humid air instability of CsPbI₂Br perovskite solar cells (PSCs) hinders their further development. The optoelectronic properties of CsPbI₂Br films are closely related to the quality of films, so preparing high-quality perovskite films is crucial for fabricating high-performance PSCs. For the first time, we demonstrate that the regulation of ambient temperature of the dry air in the glovebox is able to control the growth of CsPbI₂Br crystals and further optimize the morphology of CsPbI₂Br film. Through controlling the ambient air temperature assisted crystallization, high-quality CsPbI₂Br films are obtained, with advantages such as larger crystalline grains, negligible crystal boundaries, absence of pinholes, lower defect density, and faster carrier mobility. Accordingly, the PSCs based on as-prepared CsPbI₂Br film achieve a power conversion efficiency of 15.5% (the maximum stabilized power output of 15.02%). Moreover, the optimized CsPbI₂Br films show excellent robustness against moisture and oxygen and maintain the photovoltaic dark phase after 3 h aging in an air atmosphere at room temperature and 35% relative humidity (R.H.). In comparison, the pristine films are completely converted to the yellow phase in 1.5 h.     

The Role of Dimethylammonium Iodide in CsPbI3 Perovskite Fabrication: Additive or Dopant?

The controllable growth of CsPbI₃ perovskite thin films with desired crystal phase and morphology is crucial for the development of high efficiency inorganic perovskite solar cells (PSCs). The role of dimethylammonium iodide (DMAI) used in CsPbI₃ perovskite fabrication was carefully investigated. We demonstrated that the DMAI is an effective volatile additive to manipulate the crystallization process of CsPbI₃ inorganic perovskite films with different crystal phases and morphologies. The thermogravimetric analysis results indicated that the sublimation of DMAI is sensitive to moisture, and a proper atmosphere is helpful for the DMAI removal. The time‐of‐flight secondary ion mass spectrometry and nuclear magnetic resonance results confirmed that the DMAI additive would not alloy into the crystal lattice of CsPbI₃ perovskite. Moreover, the DMAI residues in CsPbI₃ perovskite can deteriorate the photovoltaic performance and stability. Finally, the PSCs based on phenyltrimethylammonium chloride passivated CsPbI₃ inorganic perovskite achieved a record champion efficiency up to 19.03 %.     

Lead Halide Perovskite Quantum Dots To Enhance the Power Conversion Efficiency of Organic Solar Cells

The facile synthesis, solution‐processability, and outstanding optoelectronic properties of emerging colloidal lead halide perovskite quantum dots (LHP QDs) makes them ideal candidates for scalable and inexpensive optoelectronic applications, including photovoltaic (PV) devices. The first demonstration of integrating CsPbI₃ QDs into a conventional organic solar cell (OSC) involves embedding the LHP QDs in a donor–acceptor (PTB7‐Th:PC₇₁BM) bulk heterojunction. Optimizing the loading amount at 3 wt %, we demonstrate a power conversion efficiency of 10.8 %, which is a 35 % increase over control devices, and is a record amongst hybrid ternary OSCs. Detailed investigation into the mechanisms behind the performance enhancement shows that increased light absorption is not a factor, but that increased exciton separation in the acceptor phase and reduced recombination are responsible.     

Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with Tunable Composition and Thickness by Ultrasonication

We describe the simple, scalable, single‐step, and polar‐solvent‐free synthesis of high‐quality colloidal CsPbX₃ (X=Cl, Br, and I) perovskite nanocrystals (NCs) with tunable halide ion composition and thickness by direct ultrasonication of the corresponding precursor solutions in the presence of organic capping molecules. High angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) revealed the cubic crystal structure and surface termination of the NCs with atomic resolution. The NCs exhibit high photoluminescence quantum yields, narrow emission line widths, and considerable air stability. Furthermore, we investigated the quantum size effects in CsPbBr₃ and CsPbI₃ nanoplatelets by tuning their thickness down to only three to six monolayers. The high quality of the prepared NCs (CsPbBr₃) was confirmed by amplified spontaneous emission with low thresholds. The versatility of this synthesis approach was demonstrated by synthesizing different perovskite NCs.     

Carrier dynamics in CsPbI3 perovskite microcrystals synthesized in solution phase

Carrier diffusion and recombination kinetics in all-inorganic CsPbI₃ perovskite microcrystals directly synthesized in solution phase are reported.     

Low temperature fabrication for high-performance semitransparent CsPbI2Br perovskite solar cells

All-inorganic Cs Pb I₂Br perovskite with suitable bandgap and excellent thermal stability has been reported as the most promising candidate for efficient perovskite solar cells（PSCs）. However, the high annealing temperature（> 250 °C） and poor stability of α-Cs Pb I₂Br greatly limit the future application in photovoltaic field. Herein, a facile method is reported to prepare α-Cs Pb I₂Br perovskite film with high stability at low temperature（70 °C） by incorporat...     

Soft Lattice and Defect Covalency Rationalize Tolerance of β‐CsPbI3 Perovskite Solar Cells to Native Defects

Although all‐inorganic metal halide perovskites (MHPs) have shown tremendous improvement, they are still inferior to the hybrid organic–inorganic MHPs in efficiency. Recently, a conceptually new β‐CsPbI₃ perovskite reached 18.4 % efficiency combined with good thermodynamic stability at ambient conditions. We use ab initio non‐adiabatic molecular dynamics to show that native point defects in β‐CsPbI₃ are generally benign for nonradiative charge recombination, regardless of whether they introduce shallow or deep trap states. These results indicate that MHPs do not follow the simple models used to explain defect‐mediated charge recombination in the conventional semiconductors. The strong tolerance is due to the softness of the perovskite lattice, which permits separation of electrons and holes upon defect formation, and only allows carriers to couple to the low‐frequency vibrations. Both factors decrease notably the non‐adiabatic coupling and slow down the dissipation of energy to heat.     

Alkyl-Chain-Regulated Charge Transfer in Fluorescent Inorganic CsPbBr3 Perovskite Solar Cells

Improved charge extraction and wide spectral absorption promote power conversion efficiency of perovskite solar cells (PSCs). The state-of-the-art carbon-based CsPbBr₃ PSCs have an inferior power output capacity because of the large optical band gap of the perovskite film and the high energy barrier at perovskite/carbon interface. Herein, we use alkyl-chain regulated quantum dots as hole-conductors to reduce charge recombination. By precisely controlling alkyl-chain length of ligands, a balance between the surface dipole induced charge coulomb repulsive force and quantum tunneling distance is achieved to maximize charge extraction. A fluorescent carbon electrode is used as a cathode to harvest the unabsorbed incident light and to emit fluorescent light at 516 nm for re-absorption by the perovskite film. The optimized PSC free of encapsulation achieves a maximum power conversion efficiency up to 10.85 % with nearly unchanged photovoltaic performances under 80 %RH, 80 °C, or light irradiation in air.     

<Emphasis Type="Italic">In silico</Emphasis> study of the atomic and electronic structure of quantum dots of the CdTe family doped with atoms of rare earth elements

An in silico study of semiconductor quantum dots of the CdTe family doped with atoms of rare earth elements is performed based of density functional theory. An ab initio computer design of quantum dots based on CdTe nanoparticles doped with Eu и Gd atoms is carried out. Partial densities of states of CdTe:Eu and CdTe:Gd quantum dots are calculated and analyzed. X-ray absorption near edge (XANES) spectra near the Eu K-, L₁-, and L₃- and Gd K-, L₁-, and L₃-edges of CdTe:Eu and CdTe:Gd quantum dots are calculated. The sensitivity of XANES spectroscopy for the verification of parameters of a nanosized atomic structure of quantum dots based on CdTe particles doped with atoms of rare earth elements and the determination of the local atomic structure around the atoms of rare earth elements in quantum dots is demonstrated.     

Crucial Role of Water in the Mechanosynthesis of CsPbI3 and Other ABX3 Halides

Mechanochemical synthesis of CsPbI₃, as a model system for ABX₃ halides, was studied. Water was shown to strongly promote the kinetics of formation of CsPbI₃ from the CsI+PbI₂ mixture through increased mobility of the constituting ionic species. Since many binary and ternary halides are hygroscopic, it was concluded that the presence of small, uncontrollable and unintentional additions of water should often occur in both precursor mixtures and synthesized complex halides boosting the kinetics of formation of many, if not all, ternary organic–inorganic hybrid halides such as, for example, MAPbX₃ (X=Cl, Br, I). In addition, trace amounts of water should influence the transport characteristics of complex halides. Thus, the presence of water explains, at least partially, the huge scatter in both the reported mechanochemical reaction times necessary for obtaining single-phase APbX₃ perovskite halides and the activation energies of ionic diffusion in APbX₃.     

Alkyl‐Chain‐Regulated Charge Transfer in Fluorescent Inorganic CsPbBr3 Perovskite Solar Cells

Improved charge extraction and wide spectral absorption promote power conversion efficiency of perovskite solar cells (PSCs). The state‐of‐the‐art carbon‐based CsPbBr₃ PSCs have an inferior power output capacity because of the large optical band gap of the perovskite film and the high energy barrier at perovskite/carbon interface. Herein, we use alkyl‐chain regulated quantum dots as hole‐conductors to reduce charge recombination. By precisely controlling alkyl‐chain length of ligands, a balance between the surface dipole induced charge coulomb repulsive force and quantum tunneling distance is achieved to maximize charge extraction. A fluorescent carbon electrode is used as a cathode to harvest the unabsorbed incident light and to emit fluorescent light at 516 nm for re‐absorption by the perovskite film. The optimized PSC free of encapsulation achieves a maximum power conversion efficiency up to 10.85 % with nearly unchanged photovoltaic performances under 80 %RH, 80 °C, or light irradiation in air.     

Chemically Tailoring the Dopant Emission in Manganese-Doped CsPbCl3 Perovskite Nanocrystals

Doping in perovskite nanocrystals adopts different mechanistic approach in comparison to widely established doping in chalcogenide quantum dots. The fast formation of perovskites makes the dopant insertions more competitive and challenging. Introducing alkylamine hydrochloride (RNH₃Cl) as a promoting reagent, precise controlled doping of Mn^II in CsPbCl₃ perovskite nanocrystals is reported. Simply, by changing the amount of RNH₃Cl, the Mn incorporation and subsequent tuning in the excitonic as well as Mn d–d emission intensities are tailored. Investigations suggested that RNH₃Cl acted as the chlorinating source, controlled the size, and also helps in increasing the number of particles. This provided more opportunity for Mn ions to take part in reaction and occupied the appropriate lattice positions. Carrying out several reactions with varying reaction parameters, the doping conditions are optimized and the role of the promoting reagent for both doped and undoped systems are compared.     

Chemically Tailoring the Dopant Emission in Manganese‐Doped CsPbCl3 Perovskite Nanocrystals

Doping in perovskite nanocrystals adopts different mechanistic approach in comparison to widely established doping in chalcogenide quantum dots. The fast formation of perovskites makes the dopant insertions more competitive and challenging. Introducing alkylamine hydrochloride (RNH₃Cl) as a promoting reagent, precise controlled doping of Mn^II in CsPbCl₃ perovskite nanocrystals is reported. Simply, by changing the amount of RNH₃Cl, the Mn incorporation and subsequent tuning in the excitonic as well as Mn d–d emission intensities are tailored. Investigations suggested that RNH₃Cl acted as the chlorinating source, controlled the size, and also helps in increasing the number of particles. This provided more opportunity for Mn ions to take part in reaction and occupied the appropriate lattice positions. Carrying out several reactions with varying reaction parameters, the doping conditions are optimized and the role of the promoting reagent for both doped and undoped systems are compared.     

Novel ytterbium-doped CsPbI2Br thin-films–based inorganic perovskite solar cells toward improved phase stability

In this study, we used ytterbium (Yb²⁺) as a dopant in the CsPbI₂Br inorganic perovskite thin film and stabilized its black phase. Here, we varied the Yb²⁺ doping concentration in the CsPb_1?xYb_xI₂Br (x = 0–0.04) perovskite phase through simple solution method. The optimum concentration of Yb²⁺ showed improved morphology and crystal growth. The fabricated all-inorganic perovskite solar cells (IPVSCs) having CsPb_0.97Yb_0.03I₂Br-based champion device showed the highest 15.41% power conversion efficiency (PCE) for a small area of 0.09 cm² and 14.04% PCE for a large area of 1 × 1 cm² with excellent reproducibility, which is higher than the controlled CsPbI₂Br device. Detailed photovoltaic analysis revealed that the PCE, open-circuit voltage (V_OC), short circuit current density (J_SC) and fill factor (FF) of the final IPVSC device attributed to the suppressed charge recombination, better film quality, and well growth orientation of the perovskite film. Moreover, the champion CsPb_0.97Yb_0.03I₂Br device retains >85% initial efficiency after 280 h under 85 °C thermal annealings. Our results provide a new method to boost the performance of the photovoltaic application.     

Iodotrimethylsilane as a Reactive Ligand for Surface Etching and Passivation of Perovskite Nanocrystals toward Efficient Pure-red to Deep-red LEDs

Resurfacing perovskite nanocrystals (NCs) with tight-binding and conductive ligands to resolve the dynamic ligands—surface interaction is the fundamental issue for their applications in perovskite light-emitting diodes (PeLEDs). Although various types of surface ligands have been proposed, these ligands either exhibit weak Lewis acid/base interactions or need high polar solvents for dissolution and passivation, resulting in a compromise in the efficiency and stability of PeLEDs. Herein, we report a chemically reactive agent (Iodotrimethylsilane, TMIS) to address the trade-off among conductivity, solubility and passivation using all-inorganic CsPbI₃ NCs. The liquid TMIS ensures good solubility in non-polar solvents and reacts with oleate ligands and produces in situ HI for surface etching and passivation, enabling strong-binding ligands on the NCs surface. We report, as a result, red PeLEDs with an external quantum efficiency (EQE) of ≈23 %, which is 11.2-fold higher than the control, and is among the highest CsPbI₃ PeLEDs. We further demonstrate the universality of this ligand strategy in the pure bromide system (CsPbBr₃), and report EQE of ≈20 % at 640, 652, and 664 nm. This represents the first demonstration of a chemically reactive ligand strategy that applies to different systems and works effectively in red PeLEDs spanning emission from pure-red to deep-red.     

Channeling Exciton Migration into Electron Transfer in Formamidinium Lead Bromide Perovskite Nanocrystal/Fullerene Composites

Hydrophobically capped nanocrystals of formamidinium lead bromide (FAPbBr₃) perovskite (PNC) show bright and stable fluorescence in solution and thin‐film states. When compared with isolated PNCs in a solution, close‐packed PNCs in a thin film show extended fluorescence lifetime (ca. 4.2 μs), which is due to hopping or migration of photogenerated excitons among PNCs. Both fluorescence quantum efficiency and lifetime decrease in a PNC thin film doped with fullerene (C₆₀), which is attributed to channeling of exciton migration into electron transfer to C₆₀. On the other hand, quenching of fluorescence intensity of a PNC solution is not accompanied by any change in fluorescence lifetime, indicating static electron transfer to C₆₀ adsorbed onto the hydrophobic surface of individual PNCs. Exciton migration among close‐packed PNCs and electron transfer to C₆₀ places C₆₀‐doped PNC thin films among cost‐effective antenna systems for solar cells.