Buried Interface Modulation via Preferential Crystallization in All-Inorganic Perovskite Solar Cells: The Case of Multifunctional Ti3C2Tx

Despite inorganic CsPbI_3−xBr_x perovskite solar cells (PSCs) being promising in thermal stability, the perovskite degradation and severe nonradiative recombination at the interface hamper their further development. Herein, the typical MXene material, that is, Ti₃C₂T_x, is employed to be the buried interface prior to the perovskite absorber layer in the device, which multi-functionalizes the as-prepared electron-transfer layers by means of both fascinating preferential crystallization of perovskite and/or accelerating the charge extraction with respect to an ideal energy-level alignment and suppressed trap states. Accordingly, the power conversion efficiency of the modified PSC device is substantially enhanced by as high as 19.56% in comparison to their counterparts with only the pristine CsPbI_3−xBr_x active layer. More importantly, MXene modification is favorable to improve the wettability of perovskite precursor solution with enhanced grain size and crystallinity, thereby increasing the UV long-term stability of solar cells. This work provides a new paradigm toward alleviating the severe nonradiative recombination at the interface in the device whilst enhancing the long-term stability via the preferential crystallization process.     

Anti-solvent engineering via potassium bromide additive for highly efficient and stable perovskite solar cells

Anti-solvent assisted crystallization is commonly employed method to achieve high-quality perovskites attributed to its great operability. Herein, we report an anti-solvent engineering approach via simply using potassium bromide (KBr) additive with commonly used chlorobenzene (CB) in triple-cation perovskite solar cells (PSCs). We show that the KBr additive in the CB anti-solvent not only increases the crystallinity and passivates the perovskite top surface defects, but also leads to suppressed nonradiative recombination and facilitates charge extraction at interfaces. Interestingly, due to the halide vacancies filling with K⁺ ions, hysteresis behavior in the treated perovskite layer was suppressed. Consequently, a champion power conversion efficiency (PCE) of 18.29% was yielded for anti-solvent engineering employing KBr (an 20% improvement in PCE compared to the CB-only anti-solvent device). Furthermore, the optimized device based on KBr demonstrated improved stability, maintaining 80% of its original efficiency after aging in an environment with a relative humidity of 30–50% for 1080 h. Our study reports the significant role of anti-solvent engineering in improving perovskite's quality for efficient PSCs and develops the potential for PSC commercialization.     

Samarium-Doped Nickel Oxide for Superior Inverted Perovskite Solar Cells: Insight into Doping Effect for Electronic Applications

Hole transport layers (HTLs) play a key role in perovskite solar cells (PSCs), particularly in the inverted PSCs (IPSCs) that demand more in its stability. In this study, samarium-doped nickel oxide (Sm:NiO_x) nanoparticles are synthesized via a chemical precipitation method and deposited as a hole transport layer in the IPSCs. Sm³⁺ doping can reduce the formation energy of Ni vacancy and naturally increase the density of Ni vacancies, thereby rendering increased hole density. Thenceforth, the electronic conductivity is enhanced significantly, and work function enlarged in the Sm:NiO_x film in favor of extracting holes and suppressing charge recombination. Consequently, the Sm:NiO_x-based IPSCs attain outstanding power conversion efficiencies as high as 20.71%. Even when it is applied in flexible solar cells, it still outputs efficiency as high as 17.95%. More importantly, the Sm:NiO_x is compatible with large-scale processing whereby the large area IPSCs of 1.0 cm² and 40 × 40 mm² deliver high efficiencies of 18.51% and 15.27%, respectively, all are among the highest for the inorganic HTLs based IPSCs. This research demonstrates that, while revealing the doping effect in depth, Sm:NiO_x can be a promising hole transport material for fabricating efficient, large-area, and flexible IPSCs in the future.     

An Interdiffusion Method for Highly Performing Cesium/Formamidinium Double Cation Perovskites

The fabrication of high‐quality cesium (Cs)/formamidinium (FA) double‐cation perovskite films through a two‐step interdiffusion method is reported. Cs_x FA_1‐x PbI_{3‐y(1‐x )}Br_{y(1‐x )} films with different compositions are achieved by controlling the amount of CsI and formamidinium bromide (FABr) in the respective precursor solutions. The effects of incorporating Cs⁺ and Br^? on the properties of the resulting perovskite films and on the performance of the corresponding perovskite solar cells are systematically studied. Small area perovskite solar cells with a power conversion efficiency (PCE) of 19.3% and a perovskite module (4 cm²) with an aperture PCE of 16.4%, using the Cs/FA double cation perovskite made with 10 mol% CsI and 15 mol% FABr (Cs_0.1FA_0.9PbI_2.865Br_0.135) are achieved. The Cs/FA double cation perovskites show negligible degradation after annealing at 85 °C for 336 h, outperforming the perovskite materials containing methylammonium (MA).     

Surface Defects Management by In Situ Etching with Methanol for Efficient Inverted Inorganic Perovskite Solar Cells

Inorganic perovskite solar cells (IPSCs) have developed rapidly due to their good thermal stability and the bandgap suitable for perovskite/silicon tandem solar cells. However, the large open-circuit voltage (V_OC) deficit derived from the surface defects and the energy level structure mismatch impede the development of device performance, especially in the P-I-N structure IPSCs. Herein, an innovative in situ etching (ISE) treatment method is proposed to reduce surface defects through methanol without additional passivator. It is found that the perovskite films treated with methanol result in a slight excess of PbI₂ on the surface and inserted into the grain boundaries. Therefore, the successful decrease of surface defects by methanol and the passivation of grain boundary defects by PbI₂ greatly reduce the trap density of perovskite films. And the larger work function of PbI₂ contributes to the energy band of perovskite surface bending downward and forms gradient energy level alignment at the I/N interface, which accelerates extraction of charge carriers. As a result, the efficiency of CsPbI_2.85Br_0.15 inverted IPSC is enhanced from 16.00% to 19.34%, which is one of the mostly efficient IPSCs. This work provides an original idea without additional passivator to manage the defects of inorganic perovskite.     

Vapor Phase Growth of Centimeter-Sized Band Gap Engineered Cesium Lead Halide Perovskite Single-Crystal Thin Films with Color-tunable Stimulated Emission

Single crystal metal halide perovskites thin films are considered to be a promising optical, optoelectronic materials with extraordinary performance due to their low defect densities. However, it is still difficult to achieve large-scale perovskite single-crystal thin films (SCTFs) with tunable bandgap by vapor-phase deposition method. Herein, the synthesis of CsPbCl_3(1–x)Br_3x SCTFs with centimeter size (1 cm × 1 cm) via vapor-phase deposition is reported. The Br composition of CsPbCl_3(1–x)Br_3x SCTFs can be gradually tuned from x = 0 to x = 1, leading the corresponding bandgap to change from 2.29 to 2.91 eV. Additionally, an low-threshold (≈23.9 µJ cm⁻²) amplified spontaneous emission is achieved based on CsPbCl_3(1–x)Br_3x SCTFs at room temperature, and the wavelength is tuned from 432 to 547 nm by varying the Cl/Br ratio. Importantly, the high-quality CsPbCl_3(1–x)Br_3x SCTFs are ideal optical gain medium with high gain up to 1369.8 ± 101.2 cm⁻¹. This study not only provides a versatile method to fabricate high quality CsPbCl_3(1–x)Br_3x SCTFs with different Cl/Br ratio, but also paves the way for further research of color-tunable perovskite lasing.     

Chromium-Based Metal–Organic Framework as A-Site Cation in CsPbI2Br Perovskite Solar Cells

Inorganic CsPbI_xBr_3−x perovskite solar cells (PSCs) have gained enormous interest due to their excellent thermal stabilities. However, their intrinsically poor moisture stability hampers their further development. Herein, a chromium-based metal–organic framework group is intercalated inside the inorganic Pb I framework, resulting in a new multiple-dimensional electronically coupled CsPbI₂Br perovskite. In this structurally and electronically coupled perovskite, the π-conjugated terpyridyl can delocalize the excited valence electrons of metal Cr³⁺ ion, enabling multi-interactive charge-carrier transport channels within CsPbI₂Br perovskites. The stability and efficiency of the produced devices are substantially enhanced in comparison to their counterparts with only a pristine CsPbI₂Br active layer. The optimized all-inorganic PSC yields a power conversion efficiency (PCE) as high as 17.02%. Remarkably, the stabilized device retains 80% of its PCE after 1000 h in the ambient atmosphere. This study provides a new paradigm toward addressing the stability challenge of the inorganic perovskite while enhancing its carrier transport ability.     

A Universal Strategy of Perovskite Ink - Substrate Interaction to Overcome the Poor Wettability of a Self-Assembled Monolayer for Reproducible Perovskite Solar Cells

Perovskite solar cells employing [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled monolayer as the hole transport layer have been reported to demonstrate a high device efficiency. However, the poor perovskite wetting on Me-4PACz caused by poor perovskite ink interaction with the underlying Me-4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co-solvent system comprising dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP) is employed to improve the perovskite ink - Me-4PACz coated substrate interaction and obtain a uniform perovskite layer. In comparison to DMF- and DMSO-based inks, the inclusion of NMP shows considerably higher binding energies of the perovskite ink with Me-4PACz as revealed by density-functional theory calculations. With the optimized triple co-solvent ratio, the perovskite devices deliver high power conversion efficiencies of >20%, 19.5%, and ≈18.5% for active areas of 0.16, 0.72, and 1.08 cm², respectively. Importantly, this perovskite ink–substrate interaction approach is universal and helps in obtaining a uniform layer and high photovoltaic device performance for other perovskite compositions such as MAPbI₃, FA_1−xMA_xPbI_3–yBr_y, and MA-free FA_1−xCs_xPbI_3–yBr_y.     

Improved performance of perovskite solar cells through using (FA)x(MA)1-xPbI3 optical absorber layer

In this work, the perovskite solar cells (PSCs) were fabricated with the bandgap-tunable (FA)x(MA)1-xPbI3 absorber layers through a facile two-stage deposition route. The doping was realized by adding the formamidinium iodide (FAI) into a precursor MAI solution. Both the surface morphology and electrochemical impedance spectra (EIS) were conducted to evaluate the absorber layers or solar cells. After the optimization, the best PSC performance of 14.73% was achieved at a nominal FAI content of 12.5 at.%. The performance enhancement was attributed to both the enhancement of visible light harvesting and carrier transport capability. Besides, the stability of a PSC device based on the single MAPbI3 absorber layer was also investigated, and a power conversion efficiency (PCE) of 11.27 % remained even after laying in vacuum for 10 days.     

Controllable Perovskite Crystallization by Water Additive for High‐Performance Solar Cells

A key issue for perovskite solar cells is the stability of perovskite materials due to moisture effects under ambient conditions, although their efficiency is improved constantly. Herein, an improved CH₃NH₃PbI_3?xCl_x perovskite quality is demonstrated with good crystallization and stability by using water as an additive during crystal perovskite growth. Incorporating suitable water additives in N,N‐dimethylformamide (DMF) leads to controllable growth of perovskites due to the lower boiling point and the higher vapor pressure of water compared with DMF. In addition, CH₃NH₃PbI_3?xCl_x · nH₂O hydrated perovskites, which can be resistant to the corrosion by water molecules to some extent, are assumed to be generated during the annealing process. Accordingly, water additive based perovskite solar cells present a high power conversion efficiency of 16.06% and improved cell stability under ambient conditions compared with the references. The findings in this work provide a route to control the growth of crystal perovskites and a clue to improve the stability of organic–inorganic halide perovskites.     

Phase Transition Induced Thermal Reversible Luminescent of Perovskite Quantum Dots Fibers

Converting and patterning high-quality perovskite quantum dots (PQDs) into flexible thin films is of great significance for high-performance solid-state optical applications. However, the poor stability and low quantum efficiency of PQDs after film formation is a big challenge hindering their usability. Here, an in situ synthesis strategy to prepare ligand-free long-term stable CsPb(Br_0.3I_0.7)₃@poly(methylmethacrylate) (PMMA) PQDs fibers with thermal responsive fluorescence performance is demonstrated. The luminescence of the CsPb(Br_0.3I_0.7)₃@PMMA PQDs fibers can rapidly and reversibly quench and recover between heating and cooling cycles. It reveals that the thermally induced phase transition of CsPb(Br_0.3I_0.7)₃ results in this thermally reversible luminescence phenomenon. This temperature-reversible luminescence characteristic not only deepens the comprehension of the temperature-dependent phase transition behavior of perovskite materials but also broadens their applications in the fields of information encryption storage, anti-counterfeiting, temperature warning, and other temperature-responsive fields.     

GGA U方法研究应变对纤锌矿ZnO能带结构的影响

基于第一性原理密度泛函理论和GGA U方法,以Zn1-xMgxO衬底的应变为例,计算了应变ZnO体材料的能带结构。同时研究了应力对ZnO材料的禁带宽度、价带分裂能以及电子和空穴有效质量的影响。研究结果表明,Mg组分不大于0.3时,ZnO/Znl-xMgxO材料禁带宽度随应力增大而增大,该结论与实验研究结果相符合。沿[00k] 和[k00]晶向,导带电子有效质量随应力增加而稍有增大,“场致分裂带”空穴有效质量随应力增大明显减小,而“轻空穴带”和“重空穴带”空穴有效质量几乎不随应力改变而变化。     

Revealing the Perovskite Film Formation Using the Gas Quenching Method by In Situ GIWAXS: Morphology,Properties, and Device Performance

The optoelectronic properties, morphology, and consequently the performance of metal halide perovskite solar cells are directly related to the crystalline phases and intermediates formed during film preparation. The gas quenching method is compatible with large-area deposition, but an understanding of how this method influences these properties and performance is scarce in the literature. Here, in situ grazing incidence wide angle X-ray scattering is employed during spin coating deposition to gain insights on the formation of MAPbI₃ and Cs_xFA_1−xPb(I_0.83Br_0.17)₃ perovskites, comparing the use of dimethyl sulfoxide (DMSO) and 2-methyl-n-pyrrolidone (NMP) as coordinative solvents. Intermediates formed using DMSO depend on the perovskite composition (e.g., Cs content), while for NMP the same intermediate [PbI₂(NMP)] is formed independently on the composition. For MAPbI₃ and Cs_xFA_1−xPb(I_0.83Br_0.17)₃ with a small amount of Cs (10% and 20%), the best efficiencies are achieved using NMP, while the use of DMSO is preferred for higher (30% and 40%) amount of Cs. The inhibition of the 2H/4H hexagonal phase when using NMP is crucial for the final performance. These findings provide a deep understanding about the formation mechanism in multication perovskites and assist the community to choose the best solvent for the desired perovskite composition aiming to perovskite-on-silicon tandem solar cells.     

δ‐CsPbI3 Intermediate Phase Growth Assisted Sequential Deposition Boosts Stable and High‐Efficiency Triple Cation Perovskite Solar Cells

Cs/FA/MA triple cation perovskite films have been well developed in the antisolvent dripping method, attributable to its outstanding photovoltaic and stability performances. However, a facile and effective strategy is still lacking for fabricating high‐quality large‐grain triple cation perovskite films via sequential deposition method a, which is one of the key technologies for high efficiency perovskite solar cells. To address this issue, a δ‐CsPbI₃ intermediate phase growth (CsPbI₃‐IPG) assisted sequential deposition method is demonstrated for the first time. The approach not only achieves incorporation of controllable cesium into (FAPbI₃)_1–x(MAPbBr₃)_x perovskite, but also enlarges the perovskite grains, manipulates the crystallization, modulates the bandgap, and improves the stability of final perovskite films. The photovoltaic performances of the devices based on these Cs/FA/MA perovskite films with various amounts of the δ‐CsPbI₃ intermediate phase are investigated systematically. Benefiting from moderate cesium incorporation and intermediate phase‐assisted grain growth, the optimized Cs/FA/MA perovskite solar cells exhibit a significantly improved power conversion efficiency and operational stability of unencapsulated devices. This facile strategy provides new insights into the compositional engineering of triple or quadruple cation perovskite materials with enlarged grains and superior stability via a sequential deposition method.     

Amine‐Free Synthesis of Cesium Lead Halide Perovskite Quantum Dots for Efficient Light‐Emitting Diodes

Cesium lead halide perovskite quantum dots (PQDs) have attracted significant interest for optoelectronic applications in view of their high brightness and narrow emission linewidth at visible wavelengths. A remaining challenge is the degradation of PQDs during purification from the synthesis solution. This is attributed to proton transfer between oleic acid and oleylamine surface capping agents that leads to facile ligand loss. Here, a new synthetic method is reported that enhances the colloidal stability of PQDs by capping them solely using oleic acid (OA). Quaternary alkylammonium halides are used as precursors, eliminating the need for oleylamine. This strategy enhances the colloidal stability of OA capped PQDs during purification, allowing us to remove excess organic content in thin films. Inverted red, green, and blue PQD light‐emitting diodes (LED) are fabricated for the first time with solution‐processed polymer‐based hole transport layers due to higher robustness of OA capped PQDs to solution processing. The blue and green LEDs exhibit threefold and tenfold improved external quantum efficiency (EQE), respectively, compared to prior related reports for amine/ammonium capped cross‐linked PQDs. The brightest blue LED based on all inorganic CsPb(Br_1?xCl_x)₃ PQDs is also reported.     

Charge‐Carrier Dynamics,Mobilities, and Diffusion Lengths of 2D–3D Hybrid Butylammonium–Cesium–Formamidinium Lead Halide Perovskites

Perovskite solar cells (PSCs) have improved dramatically over the past decade, increasing in efficiency and gradually overcoming hurdles of temperature‐ and humidity‐induced instability. Materials that combine high charge‐carrier lifetimes and mobilities, strong absorption, and good crystallinity of 3D perovskites with the hydrophobic properties of 2D perovskites have become particularly promising candidates for use in solar cells. In order to fully understand the optoelectronic properties of these 2D–3D hybrid systems, the hybrid perovskite BA_x(FA_0.83Cs_0.17)_1‐xPb(I_0.6Br_0.4)₃ is investigated across the composition range 0 ≤ x ≤ 0.8. Small amounts of butylammonium (BA) are found that help to improve crystallinity and appear to passivate grain boundaries, thus reducing trap‐mediated charge‐carrier recombination and enhancing charge‐carrier mobilities. Excessive amounts of BA lead to poor crystallinity and inhomogeneous film formation, greatly reducing effective charge‐carrier mobility. For low amounts of BA, the benevolent effects of reduced recombination and enhanced mobilities lead to charge‐carrier diffusion lengths up to 7.7 µm for x = 0.167. These measurements pave the way for highly efficient, highly stable PSCs and other optoelectronic devices based on 2D–3D hybrid materials.     

Passivating {100} Facets of PbS Colloidal Quantum Dots via Perovskite Bridges for Sensitive and Stable Infrared Photodiodes

Solution-processed PbS colloidal quantum dots (CQDs) are promising optoelectronic materials for next-generation infrared imagers due to their monolithic integratability with silicon readout circuit and tunable bandgap controlled by CQDs size. However, large-size PbS CQDs (diameter >4 nm) for longer shortwave-infrared photodetection consist mainly of {100} facets with incomplete surface passivation and unsatisfied stability. Here, it is reported that perovskite-bridged PbS CQDs, in which the {100} facets of the CQDs are epitaxially bridged with CsPbI_3–xBr_x perovskite, can achieve improved passivation and enhanced stability in comparison with the traditional strategies. The resultant infrared CQDs photodiodes exhibit significantly reduced dark current, nearly 50% enhanced photoresponse, and improved work stability. These superior properties synergistically produce the most balanced performance (with a high −3 dB bandwidth of 42 kHz and an impressive specific detectivity of 6.2 × 10¹² Jones) among the reported CQDs photodetectors.     

All‐Inorganic Bismuth‐Based Perovskite Quantum Dots with Bright Blue Photoluminescence and Excellent Stability

Lead halide perovskite quantum dots (QDs) possess color‐tunable and narrow‐band emissions and are very promising for lighting and display applications, but they suffer from lead toxicity and instability. Although lead‐free Bi‐based and Sn‐based perovskite QDs (CsSnX₃, Cs₂SnX₆, and (CH₃NH₃)₃Bi₂X₉) are reported, they all show low photoluminescence quantum yield (PLQY) and poor stability. Here, the synthesis of Cs₃Bi₂Br₉ perovskite QDs with high PLQY and excellent stability is reported. Via a green and facile process using ethanol as the antisolvent, as‐synthesized Cs₃Bi₂Br₉ QDs show a blue emission at 410 nm with a PLQY up to 19.4%. The whole series of Cs₃Bi₂X₉ (X = Cl, Br, and I) QDs by mixing precursors can cover the photoluminescence emission range from 393 to 545 nm. Furthermore, Cs₃Bi₂Br₉ QDs show excellent photostability and moisture stability due to the all‐inorganic nature and the surface passivation by BiOBr, which enables the one‐pot synthesis of Cs₃Bi₂Br₉ QD/silica composite. A lead‐free perovskite white light‐emitting diode is fabricated by simply combining the composite of Cs₃Bi₂Br₉ QD/silica with Y₃Al₅O₁₂ phosphor. As a new member of lead‐free perovskite QDs, Cs₃Bi₂Br₉ QDs open up a new route for the fabrication of optoelectronic devices due to their excellent stability and photophysical characteristics.     

Nonfullerene Electron Transporting Material Based on Naphthalene Diimide Small Molecule for Highly Stable Perovskite Solar Cells with Efficiency Exceeding 20%

This study reports a new nonfullerene electron transporting material (ETM) based on naphthalene diimide (NDI) small molecules for use in high‐performance perovskite solar cells (PSCs). These solar cells simultaneously achieve high power conversion efficiency (PCE) of over 20% and long‐term stability. New NDI‐ID (N,N′‐Bis(1‐indanyl)naphthalene‐1,4,5,8‐tetracarboxylic diimide) consisting of an N‐substituted indane group having simultaneous alicyclic and aromatic characteristics is synthesized by a low‐cost, one‐step reaction, and facile purification method. The partially flexible characteristics of an alicyclic cyclopentene group on indane groups open the possibility of low‐temperature solution processing. The conformational rigidity and aromaticity of phenyl and alicyclic groups contribute to high temporal stability by strong secondary bonds. NDI‐ID has herringbone packed semiconducting NDI cores that exhibit up to 0.2 cm² V^?1 s^?1 electron mobility in field effect transistors. The inverted PSCs based on CH(NH₂)₂PbI_3–xBr_x with NDI‐ID ETM exhibit very high PCEs of up to 20.2%, which is better than that of widely used PCBM (phenyl‐C61‐butyric acid methyl ester) ETM‐based PSCs. Moreover, NDI‐ID‐based PSCs exhibit very high long‐term temporal stability, retaining 90% of the initial PCE after 500 h at 100 °C with 1 sun illumination without encapsulation. Therefore, NDI‐ID is a promising ETM for highly efficient, stable PSCs.     

Ultrastable and Reversible Fluorescent Perovskite Films Used for Flexible Instantaneous Display

All‐inorganic halide perovskite materials are regarded as promising materials in information display applications owing to their tunable color, narrow emission peak, and easy processability. However, the photoluminescence (PL) stability of halide perovskite films is still inferior due to their poor thermal stability and hygroscopic properties. Herein, all‐inorganic perovskite films are prepared through vacuum thermal deposition method to enhance thermal and hygroscopic stability. By intentionally adding extra bromide source, a structure of CsPbBr₃ nanocrystals embedded in a CsPb₂Br₅ matrix (CsPbBr₃/CsPb₂Br₅) is formed via an air exposure process, leading to impressive PL stability in ambient atmosphere. In addition, the as‐fabricated CsPbBr₃/CsPb₂Br₅ structure shows enhanced PL intensity due to the dielectric confinement. The CsPbBr₃/CsPb₂Br₅ structure film can almost reserve its initial PL intensity after four months, even stored in ambient atmosphere. The PL intensity for CsPbBr₃/CsPb₂Br₅ films vanishes at elevated temperature and recovers by cooling down in a short time. The reversible PL conversion process can be repeated over hundreds of times. Based on the reversible PL property, prototype thermal‐driven information display devices are demonstrated by employing heating circuits on flexible transparent substrates. These robust perovskite films with reversible PL characteristics promise an alternative solid‐state emitting display.