Centimeter-Sized Molecular Perovskite Crystal for Efficient X-Ray Detection

Molecular perovskites have demonstrated great potential for ferroelectrics and nonlinear optics; however, their charge transport properties for optoelectronics have rarely been explored. Here, understanding of charge transport behavior of molecular perovskite under X-ray excitation based on centimeter-scale TMCM-CdCl₃ (TMCM⁺, trimethylchloromethyl ammonium) single crystal is demonstrated. The crystal is fabricated from an aqueous solution and exhibits a large bandgap of 5.51 eV, with the valence band maximum mainly dominated by the Cl-p/Cd-d states and the conduction band minimum primarily by Cd-s/Cl-p states. Charge mobility exceeding 40 cm² V⁻¹ s⁻¹ and mobility–lifetime (µτ) product on the order of 10⁻⁴ cm² V⁻¹ for the crystal are observed. These excellent optoelectronic properties translate to an efficient photoresponse under X-ray excitation, with the sensitivity reaching 128.9 ± 4.64 µC Gy_air⁻¹ cm⁻² [fivefold higher than that of the commercialized amorphous selenium (α-Se)] and a low detection limit of 1.06 μC Gy_air⁻¹ s⁻¹ (10 V bias). This work pioneers a superior metal-based molecular perovskite single-crystal based paradigm for optoelectronic investigation, which may lead to the discovery of a new generation of X-ray detection and imaging materials.     

Eco-Friendly and Highly Efficient Light-Emission Ferroelectric Scintillators by Precise Molecular Design

Hybrid manganese halide has attracted much attention in the field of environment friendly ferroelectric and photo-responsive multifunctional materials. Here, the highly efficient photoluminescent inorganic framework MnBr₄²⁻ is utilized to conceive and synthesize a series of hybrid manganese bromide compounds [RQ]₂MnBr₄ by introducing precisely designed quasi-spherical cations [RQ]⁺ (R  =  H, Me, Et, FEt, Q  =  quinuclidine). The accurate and effective modification of cations not only achieves the satisfactory ferroelectricity, but also enhances the photoluminescence quantum yield from 38.7% to 83.65%. Moreover, [FEtQ]₂MnBr₄ shows a highly efficient X-ray scintillator performance, including a large range of linear response to X-ray dose rate from 0.3 to 414.2  μ Gy_air s⁻¹, a high light yield of 34 438 photons per MeV, and a low detection limit of 258 nGy_air s⁻¹. This work provides an efficient strategy for the preparation of hybrid manganese halide ferroelectrics with highly efficient light-emission and X-ray detection.     

2D-Layered Manganese Perovskite with High Mobility

2D perovskite is an organic–inorganic hybrid material with good photoelectric properties, generally prepared by using organic groups as isolation molecules. In this study, using manganese chloride and potassium halide as raw materials, all-inorganic 2D lead-free perovskites are prepared by the Bridgeman melting and cooling method. Different from the 2D perovskites synthesized by organic spacer molecules, the prepared all-inorganic 2D perovskites have smaller layer spacings and good crystallization performance due to the use of potassium halide as spacer molecules. They are direct bandgap semiconductors and their energy bandgaps are tuned by the different types of potassium halides. High degree orientation crystal thin films with (001) lattice plane parallel to silicon wafer substrate are prepared by double-source evaporation. The physical morphology of the films is characterized by grazing angle X-ray diffraction, transmission electron microscopy, and electron diffraction. The field effect transistors prepared from these 2D films show excellent electronic characteristics. The mobility of the optimized device is ≈24 cm² v⁻¹ s⁻¹ and the on/off ratio reaches 10⁵. This study reveals the potential of lead-free manganese 2D perovskite as a high-performance perovskite field effect transistor.     

Suppression of Ionic and Electronic Conductivity by Multilayer Heterojunctions Passivation Toward Sensitive and Stable Perovskite X-Ray Detectors

Organic-inorganic hybrid perovskites are promising candidates for direct X-ray detection and imaging. The relatively high dark current in perovskite single crystals (SCs) is a major limiting factor hindering the pursuit of performance and stability enhancement. In this study, the contribution of dark current is disentangled from electronic (σ_e) and ionic conductivity (σ_i) and shows that the high σ_i dominates the dark current of MAPbBr₃ SCs. A multilayer heterojunctions passivation strategy is developed that suppresses not only the σ_i by two orders of magnitude but also σ_e by a factor of 1.6. The multilayer heterojunctions passivate the halide vacancy defects and increase the electron and hole injection barrier by inducing surface p-type doping of MAPbBr₃. This enables the MAPbBr₃ SC X-ray detectors to obtain a high sensitivity of 19 370 µC Gy_air⁻¹ cm⁻² under a high electric field of 100 V cm⁻¹, a record high sensitivity for bromine self-powered devices, and a low detection limit of 42.3 nGy_air s⁻¹. The unencapsulated detectors demonstrate a stable baseline after storage for 210 days and outstanding operational stability upon irradiation with an accumulated dose of up to 1944 mGy_air.     

Inch-Size Single Crystals of Lead-Free Chiral Perovskites with Bulk Photovoltaic Effect for Stable Self-Driven X-Ray Detection

Lead halide perovskites have made great advance in direct X-ray detection, however the presence of toxic lead and the requirement of high working voltages severely limit their applicability and operational stability. Thus, exploring “green” lead-free hybrid perovskites capable of detecting X-rays at zero bias is crucial but remains toughly challenging. Here, utilizing chiral R/S-1-phenylpropylamine (R/S-PPA) cations, a pair of 0D chiral-polar perovskites, (R/S-PPA)₂BiI₅ ( 1 R / 1 S ) are constructed. Their intrinsic spontaneous electric polarization induces a large bulk photovoltage of 0.63 V, which acts as a driving force to separate and transport photogenerated carriers, thus endowing them with the capability of self-driven detection. Consequently, self-driven X-ray detectors with a low detection limit of 270 nGy s⁻¹ are successfully constructed based on high-quality, inch-sized single crystals of 1 R . Notably, they show suppressed baseline drift under the self-driven mode, exhibiting superior operational stability. This study realizes self-driven X-ray detection in a single-phase lead-free hybrid perovskite by exploiting the intrinsic bulk photovoltaic effect, which sheds light on future explorations of lead-free hybrid perovskites toward “green” self-driven radiation detectors with high performance.     

Sintered Polycrystalline BiVO4 Pellet for Stable X-Ray Detector with Low Detection Limit

Semiconductors based on Bi element show large attenuation coefficients to X-ray photons and have been recognized as candidates for X-ray detectors. However, the application of stable Bi-based oxide materials to X-ray detectors has been rarely investigated. In this research, the X-ray response of a BiVO₄ pellet has been studied. It has been found that the BiVO₄ pellet has a large resistivity of 1.3 × 10¹² Ω cm, negligible current drift of 6.18 × 10⁻⁸ nA cm⁻¹ s⁻¹ V⁻¹ under electrical bias and mobility lifetime product, µτ, of 1.75 × 10⁻⁴ cm² V⁻¹, which renders the pellet with an X-ray sensitivity of 241.3 µC Gy_air⁻¹ cm⁻² and a detection limit of 62 nGy_air s⁻¹ under 40 KVp X-ray illumination and 40 V bias voltage. The BiVO₄ pellet also shows operational stability under steady X-ray illumination with total dose of 2.01 Gy_air, equal to the dose of 20 000 medical chest X-ray inspections. This research reveals the potential application of BiVO₄ in X-ray detection devices and inspires further research in this area.     

Ceramic Wafer Scintillation Screen by Utilizing Near-Unity Blue-Emitting Lead-Free Metal Halide (C8H20N)2Cu2Br4

Scintillators with high light yield, low detection limit, large X-ray attenuation efficiency as well as stable and nontoxic compositions are of great importance for radiation detection applications. Here, 0D (C₈H₂₀N)₂Cu₂Br₄ single crystals are obtained and show blue emission peaking at 468 nm with a near-unity photoluminescence quantum yield of 99.7%, a large Stokes shift of 148 nm (i.e., negligible self-absorption), and a good environmental stability along with strong X-ray absorption capability. Moreover, a high light yield of up to ≈ 91 300 photons/MeV and a low detection limit of 52.1 nGy_air s⁻¹ are realized, which is more than one hundred times lower than the dose rate of 5.5 µGy_air s⁻¹ required for X-ray medical diagnostics. (C₈H₂₀N)₂Cu₂Br₄ ceramic wafer scintillation screen is fabricated by a cold pressing sintering process, and the clear contrast images of opaque metal box and electronic component with a spatial resolution of 9.54 lp mm⁻¹ are realized. This study not only designs a new lead-free metal halide scintillator, but also develops a universal strategy for the preparation of large-sized scintillator screen in nondestructive X-ray imaging.     

Discovering New Type of Lead-Free Cluster-Based Hybrid Double Perovskite Derivatives with Chiral Optical Activities and Low X-Ray Detection Limit

2D chiral hybrid perovskites have recently emerged as outstanding semiconductor materials. However, most of the reported 2D chiral perovskites have limited structural types and contain high levels of toxic lead, which severely hinders their further applications. Herein, by using a mixed-cation strategy, an unprecedented type of lead-free cluster-based 2D chiral hybrid double perovskite derivatives are successfully obtained, [(R/S-PPA)₄(IPA)₆Ag₂Bi₄I₂₄]·2H₂O ( 1-R and 1-S ), and [(R/S-PPA)₄(n-BA)₆Ag₂Bi₄I₂₄]·2H₂O ( 2-R and 2-S ) (R/S-PPA=R/S–1-phenylpropylamine; IPA=isopentylamine; n-BA=n-butylamine). Their inorganic skeletons are linked by binuclear {Bi₂I₁₀} and infinite chain {Ag₂Bi₂I₁₄}_∞, in which bismuth clusters and multiple coordination modes (e.g., tetrahedral AgI₄ and octahedral AgI₆) are introduced into the double perovskite system for the first time. This introduction induces distortion of the inorganic layer, which may facilitate the transfer of chirality from the chiral cations into achiral double perovskite skeletons. Further, circular dichroism measurements and circularly polarized light detection confirm their inherent chiral optical activities. In addition, 1-S exhibits an ultralow X-ray detection limit of 129.5 nGy s⁻¹, which is 42-fold lower than that of demands in regular medical diagnosis (5.5 µGy s⁻¹). This study provides a pathway to construct novel type of lead-free cluster-based double perovskite derivatives.     

The First Improper Ferroelectric of 2D Multilayered Hybrid Perovskite Enabling Strong Tunable Polarization-Directed Second Harmonic Generation Effect

2D organometallic halide perovskites are recently emerging as a robust family of ferroelectrics, of which their inherent spontaneous polarization (P_s) endows fascinating quadratic nonlinear optical properties. However, up to date, few studies are reported to tune and control the second harmonic generation (SHG) effect in this ferroelectric branch. Herein, the first improper ferroelectric of 2D multilayered hybrid perovskites, (IA)₂(EA)₂Pb₃Br₁₀ ( 1 , where IA is isoamylammonium and EA is ethylammonium), which exhibits a high Curie temperature ( ≈ 371 K) and biaxial ferroelectricity with P_s of 2.2  µ C cm⁻² is reported. Strikingly, its unique in-plane ferroelectricity allows strong tunable SHG properties under the polarized-light. That is, the maximum SHG signals are observed with polarized-light parallel to P_s, while the minimum SHG appears along the vertical direction. This SHG anisotropy creates an extremely large dichroism ratio of ≈ 12, as visualized by 2D color mapping, which is the record-high merit for this type of SHG systems. To the best knowledge, this is the first time to achieve tunable SHG effects through ferroelectric polarization. As a pioneering study, the coupling between the SHG effect and ferroelectricity paves a new direction of 2D hybrid perovskite ferroelectrics toward smart optical device applications.     

2D Hybrid Perovskite Ferroelectric Enables Highly Sensitive X‐Ray Detection with Low Driving Voltage

X‐ray detectors with high sensitivity are of great significance in both civil and military fields. Over the past decades, great efforts have been made to improve the sensitivity in conventional inorganic materials, but mainly at the cost of increasing the energy consumption with a quite high operating voltage. Developing photosensitive ferroelectrics directly as detector materials may be a conceptually new strategy in view of the strong ferroelectric spontaneous polarization (P_s) that assists photoinduced carriers separation and transport. A high‐performance X‐ray detector in 2D hybrid halide perovskite ferroelectric (C₄H₉NH₃)₂(C₂H₅NH₃)₂Pb₃Br₁₀ ( BA₂EA₂Pb₃Br₁₀ ) (P_s = 5 µC cm^?2) is fabricated and exhibits an ultrahigh X‐ray sensitivity up to 6.8 × 10³ µC Gy_air^?1 cm^?2 even at a relatively low operating voltage, which is over 300‐fold larger than that of state‐of‐the‐art α‐Se X‐ray detectors. Such a brilliant figure‐of‐merit is largely attributed to the superior mobility–lifetime products associated with the strong ferroelectric polarization of BA₂EA₂Pb₃Br₁₀ . As pioneering work, these findings inform the exploration of hybrid halide perovskite ferroelectrics toward high‐performance photoelectronic devices.     

Synthesis of 0D Manganese-Based Organic–Inorganic Hybrid Perovskite and Its Application in Lead-Free Red Light-Emitting Diode

Lead-based perovskite light-emitting diodes (PeLEDs) have exhibited excellent purity, high efficiency, and good brightness. In order to develop nontoxic, highly luminescent metal halide perovskite materials, tin, copper, germanium, zinc, bismuth, and other lead-free perovskites have been developed. Here, a novel 0D manganese-based (Mn-based) organic–inorganic hybrid perovskite with the red emission located at 629 nm, high photoluminescence quantum yield of 80%, and millisecond level triplet lifetime is reported. When applied as the emissive layer in the PeLEDs, the maximum recording brightness of devices after optimization is 4700 cd m⁻², and the peak external quantum efficiency is 9.8%. The half-life of the device reaches 5.5 h at 5 V. The performance and stability of Mn-based PeLEDs are one order of magnitude higher than those of other lead-free PeLEDs. This work clearly shows that the Mn-based perovskite will provide another route to fabricate stable and high-performance lead-free PeLEDs.     

Stereo-Active Lone Pairs Induced Giant Polarization in a 2D Ge-Based Halide Perovskite Antiferroelectric

Antiferroelectrics, characterized by electrically controlled antipolar-polar phase transformation, have attracted tremendous attention as a class of promising electroactive materials for assembling electronic devices. The emerging two-dimensional (2D) halide perovskites with superior compositional diversity offer an ideal platform for exploring electroactive materials, whereas lead-free antiferroelectric counterparts are still scarcely reported. Herein, for the first time, a new lead-free 2D germanium iodide perovskite antiferroelectric (i-BA)₂CsGe₂I₇ ( 1 , i-BA is iso-butylammonium) has been presented, which exhibits a high Curie temperature (T_c) up to 403 K. Remarkably, benefiting from the lone pair stereochemical activity in Ge²⁺ induced large structural distortion and Cs⁺ ion off-center displacement, 1 shows well-defined double P–E hysteresis loops in a wide temperature range with a giant maximum polarization up to 18.8 µC cm⁻², which achieves a new high record among molecular antiferroelectrics. Moreover, under a low external electric field of 22.5 kV cm⁻¹, the antipolar-polar phase transformation in 1 affords a recoverable energy storage density W_rec of 0.27 J cm⁻³ and high storage efficiency up to 79.76%. Such lead-free halide perovskite antiferroelectric with intriguing antiferroelectric behaviors, including high T_c, large polarization and remarkable energy storage properties, is exciting, which provides an alternative candidate for high-performance antiferroelectrics for environmentally friendly electronic devices.     

Fluorinated Organic A-Cation Enabling High-Performance Hysteresis-Free 2D/3D Hybrid Tin Perovskite Transistors

2D tin-based perovskites have gained considerable attention for use in diverse optoelectronic applications, such as solar cells, lasers, and thin-film transistors (TFTs), owing to their good stability and optoelectronic properties. However, their intrinsic charge-transport properties are limited, and the insulating bulky organic ligands hinder the achievement of high-mobility electronics. Blending 3D counterparts into 2D perovskites to form 2D/3D hybrid structures is a synergistic approach that combine the high mobility and stability of 3D and 2D perovskites, respectively. In this study, reliable p-channel 2D/3D tin-based hybrid perovskite TFTs comprising 3D formamidinium tin iodide (FASnI₃) and 2D fluorinated 4-fluoro-phenethylammonium tin iodide ((4-FPEA)₂SnI₄) are reported. The optimized FPEA-incorporated TFTs show a high hole mobility of 12 cm² V⁻¹ s⁻¹, an on/off current ratio of over 10⁸, and a subthreshold swing of 0.09 V dec⁻¹ with negligible hysteresis. This excellent p-type characteristic is compatible with n-type metal-oxide TFT for constructing complementary electronics. Two procedures of antisolvent engineering and device patterning are further proposed to address the key concern of low-performance reproducibility of perovskite TFTs. This study provides an alternative A-cation engineering method for achieving high-performance and reliable tin-halide perovskite electronics.     

Mixed Halide Formation in Lead-Free Antimony-Based Halide Perovskite for Boosted CO2 Photoreduction: Beyond Band Gap Tuning

Photocatalytic conversion of carbon dioxide (CO₂) into value-added fuels is a vastly promising anthropogenic chemical carbon cycle to combat the greenhouse effect while meeting the ever-increasing energy demand. Recently, lead-based halide perovskites have demonstrated great potential in various applications including photochemical reduction of CO₂. However, in view of lead toxicity, the exploration of a lead-free alternative is crucial for long term application. Herein, a series of lead-free mixed halide perovskites Cs₃Sb₂Cl_xBr_9−x (0 ≤ x ≤ 9) is prepared via a facile antisolvent recrystallization technique, where the incorporation of a secondary halide enhances the charge transfer and separation while allowing precise tuning of bandgap between 2.59 and 2.90 eV. Theoretical calculations further reveal that the formation of mixed Cl/Br halides engenders favorable charge redistribution due to lower octahedral distortion, which in turn strengthens CO₂ adsorption and activation. Under visible light illumination, the optimal dual halide perovskite, Cs₃Sb₂Cl₄Br₅ manifests substantial twofold and fourfold enhancements of CH₄ yield over the single halide perovskite, Cs₃Sb₂Br₉ and Cs₃Sb₂Cl₉, respectively. In brief, this study provides a compelling demonstration of lead-free mixed halide perovskites for photocatalytic CO₂ reduction, and it is anticipated to drive further application of perovskite-based photocatalysts toward a diverse range of artificial photoredox reactions.     

Lone-pair Electrons Enhancement Effect: SnTe3O8 Hard X-ray Detection with Stable High-temperature Sensitivity and Ultralow Detection Limit

Sensitivity and detection limit of X-ray detectors are crucial for security checks, medical diagnoses, and industrial inspections. In this study, it is reported that introducing some cations containing lone-pair electrons is beneficial for enhancing the Compton scattering effect and thus improving X-ray detection performance. As an example, SnTe₃O₈ is selected and grown as a novel high-temperature X-ray detection crystal. Because of the high resistivity of 2 × 10¹⁴ Ω cm and high mobility lifetime product of 3.22 × 10⁻⁴ cm² V⁻¹, SnTe₃O₈ X-ray detector exhibits a high sensitivity of 436 µC Gy_air⁻¹ cm⁻² under 120 keV hard X-ray, a low dark current drift of 2.44 × 10⁻⁹ nA cm⁻¹ s⁻¹ V⁻¹ and a record low detection limit of 8.19 nGy_air s⁻¹ among all oxide X-ray detectors. Furthermore, the high-temperature sensitivity of SnTe₃O₈ X-ray detector is enhanced to 617 µC Gy_air⁻¹ cm⁻² at 175 °C, which is ≈31 times larger than that of the commercial α-Se. The high thermal stability and stable high-temperature sensitivity of SnTe₃O₈ single crystal X-ray detectors have potential applications in high-temperature environments. The results not only provide an excellent high-temperature X-ray detection crystal but also propose an effective method to explore X-ray detector materials with excellent performances.     

A Large Bandgap Organic Salt Dopant for Sn-Based Perovskite Thin-Film Transistor

Metal halide perovskite optoelectronic devices have made significant progress over the past few years, but precise control of charge carrier density through doping is essential for optimizing these devices. In this study, the potential of using an organic salt, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, as a dopant for Sn-based perovskite devices, is explored. Under optimized conditions, the thin film transistors based on the doped 2D/3D perovskite PEAFASnI₃ demonstrate remarkable improvement in hole mobility, reaching 7.45 cm²V⁻¹s⁻¹ with a low subthreshold swing and the smallest sweep hysteresis (ΔV_hysteresis = 2.27 V) and exceptional bias stability with the lowest contact resistance (2.2 kΩ cm). The bulky chemical structure of the dopant prevents it from penetrating the perovskite lattice and also surface passivation against Sn oxidation due to its hydrophobic nature surface. This improvement is attributed to the bifunctional effect of the dopant, which simultaneously passivates defects and improves crystal orientation. These findings provide new insights into potential molecular dopants that can be used in metal halide perovskite devices.     

Multi-Stage Phase-Segregation of Mixed Halide Perovskites under Illumination: A Quantitative Comparison of Experimental Observations and Thermodynamic Models

Photo- and charge-carrier-induced ion migration is a major challenge when utilizing metal halide perovskite semiconductors for optoelectronic applications. For mixed iodide/bromide perovskites, the compositional instability due to light- or electrical bias induced phase-segregation restricts the exploitation of the entire bandgap range. Previous experimental and theoretical work suggests that excited states or charge carriers trigger the process, but the exact mechanism is still under debate. To identify the mechanism and cause of light-induced phase-segregation phenomena, the full compositional range of methylammonium lead bromide/iodide samples are investigated, MAPb(Br_xI_1-x)₃ with x = 0…1, by simultaneous in situ X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy during illumination. The quantitative comparison of composition-dependent in situ XRD and PL shows that at excitation densities of 1 sun, only the initial stage of photo-segregation is rationalized with the previously established thermodynamic models. However, a progression of the phase segregation is observed that is rationalized by considering long-lived accumulative photo-induced material alterations. It is suggested that (additional) photo-induced defects, possibly halide vacancies and interstitials, need to be considered to fully rationalize light-induced phase segregation and anticipate the findings to provide crucial insight for the development of more sophisticated models.     

Low-Dimensional 2-thiopheneethylammonium Lead Halide Capping Layer Enables Efficient Single-Junction Methylamine-Free Wide-Bandgap and Tandem Perovskite Solar Cells

Wide-bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open-circuit voltage (V_OC) deficit and serious photo-induced halide segregation remain the main challenges that impede their applications. Herein, a post-treatment strategy without thermal annealing is presented to form a 2D top layer of 2-thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing-free post-treatment method can more effectively passivate the defects of WBG methylamine (MA)-free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo-induced perovskite phase segregation, as compared with the thermal annealing method that yields multi-2D phases. The resulting opaque and semi-transparent 1.66 eV-bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small V_OC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA-free WBG PSCs. Consequently, four-terminal all-perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi-junction tandem solar cells.     

Strongly Luminescent Dion–Jacobson Tin Bromide Perovskite Microcrystals Induced by Molecular Proton Donors Chloroform and Dichloromethane

Lead-free 2D perovskites based on tin halide octahedron slabs with Dion–Jacobson (DJ) phases have drawn attention due to their improved stability; still, reports on light-emitting DJ lead-free perovskites are scarce. Herein, a room-temperature ligand assisted re-precipitation method is used to produce ODASnBr₄ perovskite microcrystals (ODA denotes protonated 1,8-octanediamine). After incorporating molecular dopants chloroform and dichloromethane, not only the crystallinity of the DJ perovskite phase improves, but their emission becomes much stronger due to the formation of hydrogen bonds between [SnBr₆]⁴⁻ octahedra and acidic C H proton donors. ODASnBr₄ microcrystals doped with these molecules show a high photoluminescence quantum yield (PLQY) approaching 90%, and their emission remains stable under a continuous UV irradiation, with less than 10% loss in intensity over 6 h. Moreover, by tuning the pristine ODASnBr₄ with various degrees of exposure to the molecular dopants, the maximum of their self-trapped exciton emission can be fine-tuned over a spectral range of 570–608 nm while maintaining high PLQYs of 83–88%. This provides a convenient way to adjust the spectral position of DJ perovskite emission without changing halides or A-site spacers. Thus, stable and strongly emitting lead-free DJ perovskite materials have been developed.