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.     

Encapsulating Perovskite Quantum Dots in Iron‐Based Metal–Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction

Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low‐cost CH₃NH₃PbI₃ (MAPbI₃) perovskite QDs in the pores of earth‐abundant Fe‐porphyrin based metal organic framework (MOF) PCN‐221(Fe_x) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI₃@PCN‐221(Fe_x) (x=0–1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO₂ reduction. Using water as an electron source, MAPbI₃@PCN‐221(Fe_0.2) exhibits a record‐high total yield of 1559 μmol g^?1 for photocatalytic CO₂ reduction to CO (34 %) and CH₄ (66 %), 38 times higher than that of PCN‐221(Fe_0.2) in the absence of perovskite QDs.     

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.     

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.     

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.     

Effect of Growth Temperature on the Characteristics of CsPbI3-Quantum Dots Doped Perovskite Film

In this study, adding CsPbI₃ quantum dots to organic perovskite methylamine lead triiodide (CH₃NH₃PbI₃) to form a doped perovskite film filmed by different temperatures was found to effectively reduce the formation of unsaturated metal Pb. Doping a small amount of CsPbI₃ quantum dots could enhance thermal stability and improve surface defects. The electron mobility of the doped film was 2.5 times higher than the pristine film. This was a major breakthrough for inorganic quantum dot doped organic perovskite thin films.     

Highly Efficient,Reproducible, Uniform (CH3NH3)PbI3 Layer by Processing Additive Dripping for Solution‐Processed Planar Heterojunction Perovskite Solar Cells

A processing additive dripping (PAD) approach to forming highly efficient (CH₃NH₃)PbI₃ (MAPbI₃) perovskite layers was investigated. A MAPbI₃(CB/DIO) perovskite film fabricated by this approach, which included briefly dripping chlorobenzene incorporating a small amount of diiodooctane (DIO) during casting of a MAPbI₃ perovskite precursor dissolved in dimethylformamide, exhibited superior smooth, uniform morphologies with high crystallinity and large grains and revealed completely homogeneous surface coverage. The surface coverage and morphology of the substrate significantly affected the photovoltaic performance of planar heterojunction (PHJ) perovskite solar cells (PrSCs), resulting in a power conversion efficiency of 11.45 % with high open‐circuit voltage of 0.91 V and the highest fill factor of 80.87 %. Moreover, the PAD approach could effectively provide efficient MAPbI₃(CB/DIO) perovskite layers for highly efficient, reproducible, uniform PHJ PrSC devices without performance loss or variation even over larger active areas.     

Cesium Methylammonium Lead Iodide (CsxMA1−xPbI3) Nanocrystals with Wide Range Cation Composition Tuning and Enhanced Thermal Stability of the Perovskite Phase

Cesium methylammonium lead iodide (Cs_xMA_1−xPbI₃) nanocrystals were obtained with a wide range of A-site Cs-MA compositions by post-synthetic, room temperature cation exchange between CsPbI₃ nanocrystals and MAPbI₃ nanocrystals. The alloyed Cs_xMA_1−xPbI₃ nanocrystals retain their photoactive perovskite phase with incorporated Cs content, x, as high as 0.74 and the expected composition-tunable photoluminescence (PL). Excess methylammonium oleate from the reaction mixture in the MAPbI₃ nanocrystal dispersions was necessary to obtain fast Cs-MA cation exchange. The phase transformation and degradation kinetics of films of Cs_xMA_1−xPbI₃ nanocrystals were measured and modeled using an Avrami expression. The transformation kinetics were significantly slower than those of the parent CsPbI₃ and MAPbI₃ nanocrystals, with Avrami rate constants, k, at least an order of magnitude smaller. These results affirm that A-site cation alloying is a promising strategy for stabilizing iodide-based perovskites.     

Accelerated Interfacial Charge Transfer in Br-Gradient MAPbI3-xBrx Perovskite Thin Films?

Mixed halide perovskites (MHPs) are a class of semiconductor materials with great promise for many optoelectronic applications due to their outstanding photophysical properties. Understanding and tailoring the photogenerated carrier dynamics is essential for further improvement of perovskite performance. Herein, we report a study about the carrier transport and interfacial charge transfer dynamics in Br-gradient MAPbI_3-xBr_x perovskite thin films prepared by surface ion-exchange method. Driven by the bandgap gradient in MAPbI_3-xBr_x films, the accelerated internal hole transport and enhanced interfacial extraction efficiency were both observed. Meanwhile, the interfacial electron transfer was also found to be evidently facilitated due to the surface modification during post-treatment. Our findings suggest the possibility of simultaneous acceleration of interfacial electron and hole transfer processes in halide perovskite films via surface post-treatment technique, which is of great importance in further improving the power conversion efficiency of perovskite solar cells.     

Steric Mixed‐Cation 2D Perovskite as a Methylammonium Locker to Stabilize MAPbI3

The reduced dimension perovskite including 2D perovskites are one of the most promising strategies to stabilize lead halide perovskite. A mixed‐cation 2D perovskite based on a steric phenyltrimethylammonium (PTA) cation is presented. The PTA‐MA mixed‐cation 2D perovskite of PTAMAPbI₄ can be formed on the surface of MAPbI₃ (PTAI‐MAPbI₃) by controllable PTAI intercalation by either spin coating or soaking. The PTAMAPbI₄ capping layer can not only passivate PTAI‐MAPbI₃ perovskite but also act as MA⁺ locker to inhibit MAI extraction and significantly enhance the stability. The highly stable PTAI‐MAPbI₃ based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion PCE of 21.16 %. Such unencapsulated devices retain 93 % of initial efficiency after 500 h continuous illumination. This steric mixed‐cation 2D perovskite as MA⁺ locker to stabilize the MAPbI₃ is a promising strategy to design stable and high‐performance hybrid lead halide perovskites.     

In CH3NH3PbI3 Perovskite Film,the Surface Termination Layer Dominates the Moisture Degradation Pathway

Theoretical studies have shown that surface terminations, such as MAI or PbI layers, greatly affect the environmental stability of organic–inorganic perovskite. However, until now, there has been little effort to experimentally detect the existence of MAI or PbI terminations on MAPbI₃ grains, let alone disclose their effects on the humidity degradation pathway of perovskite solar cell. Here, we successfully modified and detected the surface terminations of MAI and PbI species on polycrystalline MAPbI₃ films. MAI-terminated perovskite film followed the moisture degradation process from MAPbI₃ to hydrate MAPbI₃⋅H₂O and then into PbI₂, with penetration of water molecules being the main driving force leading to the degradation of MAPbI₃ layer by layer. In contrast, for the PbI-terminated perovskite film in a humid atmosphere, a deprotonation degradation pathway was confirmed, in which the film preferentially degraded directly from MAPbI₃ into PbI₂, here the iodine defects played a key role in promoting the dissociation of water molecules into OH⁻ and further catalyzing the decomposition of perovskite.     

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 %.     

Low‐Energy Electron‐Induced Transformations in Organolead Halide Perovskite

Methylammonium lead iodide perovskite (MAPbI₃), a prototype material for potentially high‐efficient and low‐cost organic–inorganic hybrid perovskite solar cells, has been investigated intensively in recent years. A study of low‐energy electron‐induced transformations in MAPbI₃ is presented, performed by combining controlled electron‐impact irradiation with X‐ray photoelectron spectroscopy and scanning electron microscopy. Changes were observed in both the elemental composition and the morphology of irradiated MAPbI₃ thin films as a function of the electron fluence for incident energies from 4.5 to 60 eV. The results show that low‐energy electrons can affect structural and chemical properties of MAPbI₃. It is proposed that the transformations are triggered by the interactions with the organic part of the material (methylammonium), resulting in the MAPbI₃ decomposition and aggregation of the hydrocarbon layer.     

Composition‐Dependent Hot Carrier Relaxation Dynamics in Cesium Lead Halide (CsPbX3, X=Br and I) Perovskite Nanocrystals

Cesium‐based perovskite nanocrystals (NCs) have outstanding photophysical properties improving the performances of lighting devices. Fundamental studies on excitonic properties and hot‐carrier dynamics in perovskite NCs further suggest that these materials show higher efficiencies compared to the bulk form of perovskites. However, the relaxation rates and pathways of hot‐carriers are still being elucidated. By using ultrafast transient spectroscopy and calculating electronic band structures, we investigated the dependence of halide in Cs‐based perovskite (CsPbX₃ with X=Br, I, or their mixtures) NCs on the hot‐carrier relaxation processes. All samples exhibit ultrafast (<0.6 ps) hot‐carrier relaxation dynamics with following order: CsPbBr₃ (310 fs)>CsPbBr_1.5I_1.5 (380 fs)>CsPbI₃ NC (580 fs). These result accounts for a reduced light emission efficiency of CsPbI₃ NC compared to CsPbBr₃ NC.     

Stable Perovskite Quantum Dots Coated with Superhydrophobic Organosilica Shells for White Light‐Emitting Diodes

Metalammonium lead perovskite (MAPbX₃, MA=CH₃NH₃⁺; X=Cl, Br, I) quantum dots (QDs) have attracted tremendous attention due to their outstanding optical properties. However, they usually suffer from poor stability towards water or moisture, which seriously limits their practical applications. Here, we report a simple and effective approach to improve the stability of MAPbBr₃ QDs by encapsulating them with superhydrophobic fluorinated organosilica (FSiO₂) shells. The water‐resistant stability of the superhydrophobic MAPbBr₃ QDs/FSiO₂ is significantly enhanced and they display strong fluorescence even after immersion in water for 12 hours. This method is readily extended to prepare superhydrophobic MAPbBr_2.4Cl_0.6 QDs/FSiO₂ and MAPbI₃ QDs/FSiO₂ powders. These superhydrophobic MAPbX₃ QDs/FSiO₂ can be further used to fabricate white light‐emitting diodes (LEDs) with comparable color to pure white emission.     

Electron-enriched thione enables strong Pb–S interaction for stabilizing high quality CsPbI3 perovskite films with low-temperature processing

Cesium lead iodide (CsPbI₃) perovskite is a promising photovoltaic material with a suitable bandgap and high thermal stability. However, it involves complicated phase transitions, and black-phase CsPbI₃ is mostly formed and stabilized at high temperatures (200–360 °C), making its practical application challenging. Here, for the first time, we have demonstrated a feasible route for growing high quality black-phase CsPbI₃ thin films under mild conditions by using a neutral molecular additive of 4(1H)-pyridinethione (4-PT). The resulting CsPbI₃ thin films are morphologically uniform and phase stable under ambient conditions, consisting of micron-sized grains with oriented crystal stacking. With a range of characterization experiments on intermolecular interactions, the electron-enriched thione group in 4-PT is distinguished to be critical to enabling a strong Pb–S interaction, which not only influences the crystallization paths, but also stabilizes the black-phase CsPbI₃via crystal surface functionalization. The 4-PT based CsPbI₃ achieves 13.88% power conversion efficiency in a p–i–n structured device architecture, and encapsulated devices can retain over 85% of their initial efficiencies after 20 days of storage in an ambient environment, which are the best results among fully low-temperature processed CsPbI₃ photovoltaics.

A neutral molecular additive of 4(1H)-pyridinethione (4-PT) is used for growing high quality black-phase CsPbI₃ thin films at low temperatures.     

Steric Mixed-Cation 2D Perovskite as a Methylammonium Locker to Stabilize MAPbI3

The reduced dimension perovskite including 2D perovskites are one of the most promising strategies to stabilize lead halide perovskite. A mixed-cation 2D perovskite based on a steric phenyltrimethylammonium (PTA) cation is presented. The PTA-MA mixed-cation 2D perovskite of PTAMAPbI₄ can be formed on the surface of MAPbI₃ (PTAI-MAPbI₃) by controllable PTAI intercalation by either spin coating or soaking. The PTAMAPbI₄ capping layer can not only passivate PTAI-MAPbI₃ perovskite but also act as MA⁺ locker to inhibit MAI extraction and significantly enhance the stability. The highly stable PTAI-MAPbI₃ based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion PCE of 21.16 %. Such unencapsulated devices retain 93 % of initial efficiency after 500 h continuous illumination. This steric mixed-cation 2D perovskite as MA⁺ locker to stabilize the MAPbI₃ is a promising strategy to design stable and high-performance hybrid lead halide perovskites.     

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.     

Ion‐Exchange‐Induced 2D–3D Conversion of HMA1−xFAxPbI3Cl Perovskite into a High‐Quality MA1−xFAxPbI3 Perovskite

High‐quality phase‐pure MA_1?xFA_xPbI₃ planar films (MA=methylammonium, FA=formamidinium) with extended absorption and enhanced thermal stability are difficult to deposit by regular simple solution chemistry approaches owing to crystallization competition between the easy‐to‐crystallize but unwanted δ‐FAPbI₃/MAPbI₃ and FA_xMA_1?xPbI₃ requiring rigid crystallization conditions. Here A 2D–3D conversion to transform compact 2D mixed composition HMA_1?xFA_xPbI₃Cl perovskite precursor films into 3D MA_1?xFA_xPbI₃ (x=0.1–0.9) perovskites is presented. The designed Cl/I and H/FA(MA) ion exchange reaction induced fast transformation of compact 2D perovskite film, helping to form the phase‐pure and high quality MA_1?xFA_xPbI₃ without δ‐FAPbI₃ and MAPbI₃ impurity. In all, we successfully developed a facile one‐step method to fabricate high quality phase‐pure MA_1?xFA_xPbI₃ (x=0.1–0.9) perovskite films by 2D–3D conversion of HMA_1?xFA_xPbI₃Cl perovskite. This 2D–3D conversion is a promising strategy for lead halide perovskite fabrication.