Halide perovskite semiconductors made a great impact on the field of solar cells with efficienies soaring beyond 26% [1]. On the other hand, halide perovskites are attractive materials for light emitting devices, i.e. LEDs and lasers. Perovskite lasers can be prepared from solution at low temperatures on a wide range of substrates, which provides exciting opportunities in the field of integrated optoelectronics.[2]

Amplified spontaneous emission (ASE) and optically driven lasing were achieved in so-called hybrid organic-inorganic lead halide perovskites, where the A-site cation is based on an organic compound, such as methylammonium or formamidinium. [3,4] Intriguingly, these crystalline compounds are soft and photonic nanostructures can be directly patterned into them by thermal imprint at moderate temperatures.[5]

All-inorganic halide perovskites, such as those where the A-site cation is Cs⁺, are frequently claimed to provide improved thermodynamic stability.[6] Among them, CsPbBr₃ has been shown to be an excellent gain medium for perovskite lasers in the green spectral region. [7] More recently, we could show that b-CsPbI₃ stabilized with 2.5wt% of PEO demonstrates a low lasing threshold of 45 μJ cm^-2 at room temperature with tunable emission from 714.1 nm to 723.4 nm [8]_.

For the Cl-based representative, i.e. CsPbCl₃, deposition of thin films from solution is essentially impossible due to the poor concomitant solubility of the precursor salts PbCl₂ and CsCl.[9]

Here, we will show two concepts to achieve CsPbCl₃ thin films as gain medium. As a first strategy, we use superlattice structures of PbCl₂ and CsCl with a thickness of the sublayers on the order of 3-5 nm by thermal evaporation. We evidence the formation of CsPbCl₃ at the interface of PbCl₂ and CsCl. Already a 1 nm thick CsCl layer deposited on top of PbCl₂ gives rise to a notable photoluminescence at 409 nm with a narrow line width of 8 nm (FWHM), which agrees with reports of CsPbCl₃ single crystals. The superlattices show amplified spontaneous emission (ASE) in the deep blue spectral region at 427 nm above a threshold energy density of 190 µJ/cm² at room temperature (RT).

In a second approach, we subject thin-films of CsPbBr₃ to halide exchange. Upon pulsed exposure to TiCl₄ gas in an atomic layer deposition system, the CsPbBr₃ film is step-wise converted to CsPbCl₃. Depending on the number of TiCl₄ pulses, the emission of the resulting material can be tuned between 523 nm (CsPbBr₃) to 413 nm (CsPbCl₃). Thermal imprint is shown to significantly improve the material quality affording a narrow luminescence linewidth of 8 nm (FWHM). The resulting CsPbCl₃ show ASE at 427.6 nm with a low threshold of 70 µJ/cm². Our work states the first report of CsPbCl₃ thin films showing ASE at room temperature.

Lead halide perovskite (ABX₃) nanocrystals are luminescent nanomaterials of significant interest for applications in displays, solar concentrators, and photodetectors due to their bandgap tunability across the visible spectrum, narrow emission profiles, and high radiative carrier recombination rates.[1] However, their emission properties are not uniform across the visible range. Blue emission remains challenging to achieve, while red emission often suffers from lower efficiency and stability compared to green, posing difficulties for pure perovskite-based white light generation. Porous scaffolds have been employed to fabricate various ligand-free perovskite nanostructures.[2-5] However, scaffold preparation methods have involved only the use of optically passive elements. In this work, we have developed GdVO₄:Eu³⁺ and GdVO₄:Dy³⁺ nanoparticles films with a regular pore size that can be infiltrated with perovskite precursors from the liquid phase. In this context, we prepare CsPbBr₃ and Cs₄PbBr₆ nanocrystals, which emit green and blue light respectively. Upon ultraviolet excitation, Eu³⁺-doped nanophosphors emit red light, while Dy³⁺-doped nanophosphors emit light in the blue and yellow regions of the visible spectrum.[6] The combination of perovskite nanomaterials and multifunctional phosphor-based scaffolds enables the fabrication of transparent photoluminescent coatings with tunable spectral emission, controlled by the excitation wavelength. This synergy allows for the generation of white light with customizable hues ranging from warm (2300 K) to neutral (5500 K).

Halide perovskites are forerunners for next-generation photovoltaics and light-emitting devices. The power conversion efficiencies of perovskite solar cells have exceeded 25%, while that of the external quantum efficiencies of perovskite light emitting devices have also breached the 20% mark. Their remarkable rise is driven by exceptional properties such as large absorption cross-sections, defect tolerance, significant spin-orbit coupling, long balanced charge diffusion lengths, slow hot carrier cooling, ion migration, and radiation tolerance etc. Furthermore, their versatile structures and diverse dimensionalities afford new levers for tunning their photophysical properties. Consequently, their applications have rapidly expanded beyond traditional optoelectronics into areas such as spintronics, radiation detectors, memristors, bioimaging, and quantum light sources. Of late, low dimensional halide perovskites have demonstrated great promise as single photon sources as well as bunched multiphoton sources. In this talk, I will focus on our recent efforts on the basic photophysics studies and engineering of perovskite quantum emitters [1-5].

Exciton-polaritons are half-light, half-matter excitations arising from the strong coupling regime between cavity photons and excitons of semiconductors [1]. Behaving as superlative non-linear photons due to their hybrid nature, exciton-polaritons have been providing a fruitful ground for studying quantum fluid of light and realizing prospective all-optical devices. In this presentation, we present experimental studies on exciton-polaritons in resonant metasurfaces, which are composed of sub-wavelength lattices of perovskite pillars (see Figure). Room temperature polaritons are demonstrated with a remarkable Rabi splitting in the 200 meV range. We show that polaritonic dispersion can be tailored on-demand. This includes creating linear, slow-light,  multi-valley shaped dispersions [2] as well as polarization vortex emission [3]. Finally, we observe experimentally the ballistic propagation of polaritons over hundreds of micrometers at room temperature, even with large excitonic components, some up to 80%. This long-range propagation is enabled by the high homogeneity of the metasurface, and by the large Rabi splitting which completely decouples polaritons from the phonon bath at the excitonic energy [4]. Our results suggest a new approach to study exciton-polaritons and pave the way for the development of large-scale and low-cost integrated polaritonic devices operating at room temperature.

Materials that combine optoelectronic function with control over the spin degree of freedom are central for emerging quantum technologies, opto-spintronics, and provide exciting avenues for generating polarized light-emission. Hybrid metal-halide perovskites exhibit spin-split Rashba bands and strong spin-orbit coupling, which offer directions for extended spin life-times of excited states and efficient optical spin manipulation. To achieve optimal performance in applications, an understanding how material chirality links to spin state properties and dynamics needs to be established.

In the first part of this talk, we will present our efforts on gaining control over spin state properties and dynamics in solution-processable chiral hybrid perovskites through compositional and structural tuning. For this, we tailor the chiral crystal symmetry in novel chiral lead-free bismuth-based materials, highly-emissive low-dimensional chiral lead-halide systems, as well as chiral-achiral heterostructures.

In the second part, we will discuss time- and space-resolved investigations of excited state and spin dynamics in our novel chiral perovskites. We will present results on spin dynamics from ultrafast Faraday Rotation, polarized recombination dynamics, as well as spatio-temporal imaging of excitations using ultrafast transient microscopies.

By combining the optoelectronic properties of halide perovskites (HPs) with chirality from inserted organic cations, chiral HPs brought new perspectives for chiroptical properties, such as non-linear optics or circularly polarized luminescence (CPL), or spintronic devices such as spin valves or spin-LEDs. Indeed, the emergent field of chiro-spintronics proposes to use chiral molecules as a substitute for ferromagnetic materials thanks to the spin-specific interaction between electrons and chiral molecules, a phenomenon called CISS, “chirality-induced spin selectivity”. Following this strategy, we prepared a series of chiral HPs and revealed both experimentally (mc-AFM) and theoretically (band structure and spin texture calculations) the influence of crystal symmetry elements on the spin polarization ability of this family of molecular materials (Figure a).[1] We also demonstrated the possibility to use such materials as spin valves. More recently, we reported a full series of lead-free chiral double perovskites showing strong structural distortions in the inorganic network.[2] In combination with their lead-based counterparts, such series will ultimately allow us to investigate the fundamental role of the metal ions on the CISS effect. On the other hand, revealing the ability of chiral HPs for chiroptical applications require a proper characterization of the thin film chiroptical responses, in particular circular dichroism (CD), considering the macroscopic interferences (linear dichroism LD, linear birefringence LB) inherent to solid-state samples, leading to the so-called antisymmetric LDLB effect (aLDLB) and symmetric LDLB effect (sLDLB). Since these macroscopic effects can be very strong in highly crystalline metal-halide thin films, an experimental guide to accurately discriminate between both CD, aLDLB and sLDLB was recently reported with the example of 1D chiral lead-halide networks.[3] However, in compounds with large optical anisotropy, such effects can be minimized by controlling the orientation of the polar axis with respect to the light beam propagation (Figure b). This strategy allowed us to characterize artefact-free CPL on both single crystals and thin films of 1D chiral lead-bromides with white-light emission (manuscript under revision).

The solution processed semiconductors known as perovskites, or semiconductor perovskites (SP), has been widely studied as an idoneal platform to implement cost-effective integrated lasers.  From this perspective, there is an important concern on developing a SP technology to implement photonic integrated circuits. In this context, we have recently demonstrated that a nickel acetate, Ni(AcO)₂, sol-gel is an exceptional and non-expensive matrix for SP nanocrystals. The distinctive advantage of this alternative technology relies on the in-situ crystallization of the perovskite nanocrystals during the spin-coating deposition, resulting on thin films with PL quantum yields exceeding 80 % and outstanding ambient and mechanical stability. This work successfully demonstrates the potential of Ni(AcO)₂ containing MAPbBr₃ (MA:methylamonium) SPs nanocrystals for active photonics. These nanocomposites are easily spin-coated on a SiO₂/Si to conform planar waveguides. Moreover, the concentration of nanocrystal in the matrix allows the tunability of the optical properties, resulting in thin films with a tailor-made refractive index and absorption. Under optimal concentrations, the nanocrystals are homogeneously dispersed in the film and the waveguide efficiently propagates the light with relatively low losses. Here, the excitation beam injected in the structure gives rise to the generation of photoluminescence (PL) of the nanocrystals, and under certain excitation and propagation conditions, the generation of amplified spontaneous emission (ASE) and the formation of narrow random lasing (RL) under relatively small threshold (µJ/cm²). These results mark a significant step towards realizing the potential of perovskite nanocomposites in the field of optical waveguides.

Lead halide perovskite quantum dots have recently emerged as promising nano-emitters due to their excellent optical properties, including high brightness, tunable optical bandgap, reduced blinking, and easy and low-cost fabrication [1]. These properties make them potential candidates for realising a new generation of optoelectronic devices such as light-emitting diodes (LEDs), lasers, or photodetectors. At the individual quantum dot level, single photon emission at room temperature [2,3], long coherence times and photon indistinguishability with 50% visibility at cryogenic temperatures [4,5] have also been reported. These properties suggest that perovskite quantum dots could play a key role in the realisation of efficient single-photon sources based on solution-processed nanoemitters for applications in quantum optics and quantum communication. In this context, one of the main challenges is to couple individual perovskite quantum dots to optimised photonic structures in order to control and enhance the spontaneous emission properties of the nano-emitters using cavity quantum electrodynamics (cQED) effects.

In this talk I will present our recent results on cQED experiments on single perovskite quantum dots coupled to an optical microcavity. We have designed and implemented a reconfigurable open fibre-based Fabry-Pérot microcavity, specifically suited for CsPbBr₃ perovskite quantum dots. It is based on a highly versatile setup that has previously been successfully optimised for single carbon nanotubes [6]. Unlike conventional monolithic microcavities, which are designed to ensure spatial and spectral matching to a specific nano-emitter and cannot be subsequently modified, this fibre microcavity is perfectly suited to solution-processed nano-emitters. It consists of a planar mirror on which the quantum dots are deposited and a movable concave fibre mirror. This geometry allows us both to ensure spatial and spectral matching for different perovskite quantum dots and to study the same nano-emitter in free space and in cavity configurations. I will show that previously characterised single CsPbBr₃ quantum dots [7,8] have been successfully coupled to this microcavity. By comparing their photoluminescence lifetime in free space with that in the cavity configuration, a twofold acceleration of the emission lifetime due to the Purcell effect was consistently observed, corresponding to Purcell factors of up to 4.5. Furthermore, the reversible coupling of individual CsPbBr₃ quantum dots to the cavity provides a highly interesting tool to precisely analyse the modification of the spectral features induced by the cavity coupling and to extract fundamental properties such as the vacuum Rabi coupling, which is of the order of 30 µeV in our system. These results pave the way for the realisation of a narrow-band efficient single-photon source at the cavity resonance frequency in the weak coupling regime using perovskite quantum dots.

Halide perovskites show excellent optoelectronic properties including bandgap tunability, high radiative recombination rates and narrow emission lines that make them promising candidates for the next generation solar cells, LEDs and detectors.^[1],[2],[3] Their optical properties and ease of processing make them very interesting to control light matter interactions to deliver devices with unique properties and enhanced performance. However, their thin film character is yet to be exploited to enable full control over the emission properties, something that would open avenues to surpass the luminous efficacies of conventional LEDs and facilitate their widespread adoption.

In this talk, we present a novel green perovskite LED architecture where enhanced emission and directionality on demand are achieved by means of a hybrid photonic-plasmonic structure.^[4] We show how a code based on the transfer matrix model boosted by a genetic algorithm identifies the best combination of materials and thin film thicknesses to maximise outcoupled light with very narrow and controllable angular dispersion; all in a realistic fashion compatible with the fabrication of efficient LEDs. The experimental realization of the optimum designs allows us to demonstrate devices with amplified green emission selectively enhanced at different angles. Our low temperature process can tune the perovskite thickness on a nanometric scale to enhanced electroluminescence on demand from forward direction (0°) to up to 40°. This approach expands the role of the perovskite film from a mere emitter to an active photonic layer participating in the strong interference phenomena arising from the designed photonic-plasmonic nanostructures. Our methodology is versatile and easily integrable into cost-effective perovskite LEDs with emission lines covering the entire visible spectrum. Finally, we adapt this resonant cavity concept to demonstrate a highly spectral selective and robust perovskite photodetector, showing 2.4-fold EQE enhancement at the narrowband peak with respect to a broadband photodetector counterpart of the same perovskite thickness.^[5]

Metal halide perovskites (MHPs), particularly CsPbBr₃, have emerged as a transformative material for optoelectronic applications, offering unparalleled properties such as high carrier mobility, exceptional optoelectronic performance, large photoluminescence quantum yield, and superior stability under humidity and thermal stress. Its solution processability allows for easy fabrication using inkjet printing, an environmentally sustainable alternative to conventional manufacturing techniques [1].

In inkjet printing of perovskites, the characteristics of the functional ink and printing conditions are crucial in determining the final device performance, with annealing temperature playing a critical role in influencing the crystal structure and, consequently, the optoelectronic properties of the printed films. This study comprehensively investigates the impact of annealing temperature in vacuum oven from 45-200 °C on the properties of inkjet-printed CsPbBr₃ nanocrystal films printed on glass substrate [2]. The CsPbBr₃ nanocrystal inks were prepared in the ratio of 3:1 in dodecane and hexane solvent with each nanocrystal measuring 7-13 nm and the printing was performed using Dimatix inkjet printer.

 The results reveal a significant dependence of photoluminescence (PL) intensity on the annealing temperature, with the optimal PL emission observed for devices annealed at 180°C. The change in the PL properties are related to the impact of annealing temperature on grain size, crystallinity, and film uniformity, which directly affect optoelectronic properties and stability corroborated by various characterizing techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-Vis) absorption spectroscopy providing conclusive evidence of the temperature-induced changes in crystal structure, phase purity, and optoelectronic performance. These findings underline the critical role of precise thermal processing in achieving high-performance inkjet-printed perovskite films, positioning CsPbBr₃ as a viable material to be printed on ITO coated glass substrate for LED applications [3].

Halide perovskite materials hold significant potential for solar energy and optoelectronic applications. However, enhancing their efficiency and stability necessitates addressing challenges related to lateral inhomogeneity. Photoluminescence imaging techniques are widely employed to measure their optoelectronic and transport properties¹. While achieving high precision typically requires longer acquisition times, extended light exposure can significantly alter the perovskite layers due to their high reactivity, compromising data quality.

To address this issue, we propose a method to extract high-quality lifetime images from rapidly acquired, noisy time-resolved photoluminescence images². Our approach leverages constrained reconstruction techniques, incorporating the Huber loss function and a specific form of Total Variation Regularization. This method effectively mitigates limitations imposed by local signal-to-noise ratios (SNR), allowing access to greater detail and features in the results. Through simulations and experimental validation, we demonstrate that our approach outperforms traditional pointwise techniques. Additionally, this analysis can be extended to determine the surface recombination rate, providing valuable insights for the advancement and optimization of halide perovskite materials. Furthermore, we identify optimal acceleration and optimization parameters tailored to decay time imaging of perovskite materials, offering novel perspectives for accelerated experiments essential to characterizing degradation processes.

Importantly, our methodology has broader applications. It can be extended to other beam-sensitive materials, various imaging characterization techniques, and more complex physical models for time-resolved decays.

Metal halide perovskites (MHPs) are direct bandgap semiconductors with excellent potential and perspectives to become an alternative to traditional semiconductors in the implementation of future devices for optoelectronics and photonics. Furthermore, MHPs have shown remarkable performance for potential optoelectronic applications beyond photovoltaics. The continuous development in smart devices and microsystems for the control of industrial processes, biomedical sensors and instruments, visible and NIR light communications (in the internet of things, for example), object imaging, and cameras for artificial intelligence and robotics is triggering new demands for photodetection concepts and their integration in photonic chips. However, for the explosion of such future photodetector technologies, some other requirements are important: low cost and low CO₂ footprint in fabrication, low operation voltage, small volume, high speed, flexibility, biocompatibility, solar-blind and many other features (for different applications). Therefore, a real and very interesting technology for a future generation of photodetectors can arise on the basis of MHPs, given their excellent optoelectronic properties and the fact that they can be synthesized at low temperatures via fast and simple processes, and films can be easily formed by low-cost solution processing techniques (spin-coating, spray-coating, dip-coating, doctor blading, inkjet printing). Among the MHPs, lead-free perovskite compounds are the most promising non-toxic alternative for developing photodetectors.

This study investigates the development of (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁-based photodetectors fabricated using inkjet printing on both glass and flexible substrates, emphasizing their potential for advanced optoelectronic applications. The focus is on optimizing the crystallization process of (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁ layers, ensuring high-quality films with minimal defects, and enhancing charge carrier mobility. The fabrication process employs solution-based techniques compatible with large-scale production, making the devices suitable for integration into wearable electronics and curved displays. Various strategies, such as interface engineering, compositional tuning, and passivation layers, were explored to improve stability and light sensitivity. The research demonstrates that inkjet-printed (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁ layers (200 nm thickness) exhibit uniform crystal structures, enabling high responsivity and stable performance under different environmental conditions. The fabricated devices exhibited high responsivity across a wide range of light intensities and wavelengths, including visible and near-infrared regions. Persistent photoconductivity due to carrier trapping mechanisms was observed, highlighting the need for further engineering to enhance performance stability. Photoconductive properties were evaluated using continuous and modulated light sources. Devices on glass substrates showed higher efficiency and responsivity compared to flexible PET substrates, likely due to substrate interactions and defect levels. Responsivities ranged up to 50 A/W under low light intensity, with stability improvements observed even after 30 days of operation. Notably, the devices showed improved performance over time, indicating slow film curing and effective encapsulation. The results highlight the potential of inkjet-printed (PEA_0.5,BA_0.5)₂FA₉Sn₁₀I₃₁ photodetectors for next-generation photonic applications, where flexibility and low-cost fabrication are crucial. Despite the promising performance, challenges such as sensitivity to moisture and oxidation in tin-based perovskites remain, impacting long-term device stability. This research provides valuable insights into the practical deployment of lead-free perovskites in photodetection technologies.

Halide perovskites have gained interest as light absorber materials due to their outstanding properties for optoelectronic devices, including record efficiencies in solar cells and ignited research in photodetectors. However, the challenges remain unresolved, including the inherent instability of hybrid perovskite materials and the formation of intermediate phases during solvent-based synthesis methods. To overcome these challenges, we developed the mechanosynthesis (MS) of hybrid perovskite powders and perovskite-graphite composites for visible light photodetector applications. Using this scalable and solvent-free ball-milling technique, we synthesized methylammonium lead iodide (MAPbI₃) hybrid perovskites and MAPbI₃-graphite composite powders, and characterizations have shown that nanograins (∼10 nm) in aggregates share common crystallographic orientations [1]. The synthesized composites were designated as MAPI-4h (without graphite), MAPI-Gr3%, and MAPI-Gr5%, with high yields of 86.3%, 84.3%, and 89%, respectively. The obtained powders were compacted into pellets via uniaxial compaction, and Ag electrodes were deposited on top of pellets to fabricate photodetector devices. The devices were designated as Ag-MAPI-4h, Ag-MAPI-Gr3%, and Ag-MAPI-Gr5%, respectively. The formation of ohmic contact was verified by stable linear current-voltage (I-V) curves in the dark. With the addition of Ag electrodes, the devices exhibited ten times higher current and more efficient charge extraction compared to pellets without Ag electrodes. An uniform distribution of few-layer graphite within the MAPbI₃ matrix was noticed in pellets. The effect of graphite addition was also studied for improving the photodetection performance. The Photoresponsivity was measured around 750 nm wavelength. The photoresponsivity of Ag-MAPI-Gr5%, Ag-MAPI-Gr3%, and Ag-MAPI-4h were respectively 0,13 ⅹ 10⁶ AW^-1, 7,7 ⅹ 10⁰ AW^-1, and 58,87 ⅹ 10^-3 AW^-1. Fast rise time (τ_r) and fall time (τ_f) were recorded for Ag-MAPI-4h as 1.1 s and 1.68 s, respectively, under light. Graphite should enhance the conductivity and hence the charge transport; however, it diminishes the photoresponsivity. Graphite-enhanced Raman scattering was observed with the composite with 5 wt % graphite, showing its strong resistance to photodegradation and suggesting a charge transfer between graphite and MAPbI₃. Such charge transfer is also in agreement with the quenching of the PL with an increasing amount of graphite. The presence of graphite would induce a local modification of the Coulomb interaction, “attracting” the charge carriers at the graphite and MAPbI₃ interfaces and thus favoring the charge separation and transport. This high photoconductive gain matches with the trapping of one type of charge carrier, while the other one is multiplied via injection from the contact electrodes, thus contributing even more to the photoconductivity. These results demonstrated at first the great potential of mechanosynthesis, which is a green, easy scalable and eco-friendly powder synthesis technique to develop light-sensitive materials for photovoltaic and photodetection applications.

Keywords : Mechanosynthesis of perovskites, MAPbI₃@Graphite composites, visible-light photodetectors, solvent-free synthesis, perovskite photodetectors

Halide perovskites have garnered significant attention over the past decade due to their remarkable optoelectronic properties. Perovskite light-emitting diodes (PeLEDs) have surpassed the 20% external quantum efficiency (EQE) limit for planar organic LED (OLED)-like device structures [1]. A bottom-up approach in perovskite material science highlights the potential of solution-processing techniques for device fabrication. Most high-efficiency PeLEDs reported to date have been fabricated using the spin-coating technique, which facilitates the integration of diverse materials [2]. However, spin coating is unsuitable for mass production, as it results in considerable material waste, with only a small fraction of the solution contributing to the thin-film.

Inkjet printing has emerged as a versatile and cost-effective alternative for fabricating perovskite-based devices. This technique offers high precision, scalability, and seamless integration with electronic and photonic components. Inkjet printing enables controlled deposition of materials, yielding uniform and high-quality perovskite films essential for efficient device performance. In 2020, the first PeLEDs with inkjet-printed perovskite layers were reported, achieving moderate efficiencies below 10% [3,4]. Subsequent advancements include the development of fully inkjet-printed PeLEDs [5], lead-free inkjet-printed PeLEDs [6], and the first fully inkjet-printed inorganic PeLEDs [7].

This paper reviews the key features of the inkjet printing technique, emphasizing its advantages over traditional methods, such as scalability, material efficiency, and precision in layer deposition. The discussion includes the fundamentals of solution-processing methodologies and the optimization of precursor formulations, highlighting the challenges in achieving uniform crystal formation and stable film morphology. Despite its potential, inkjet printing faces several limitations, such as coffee-ring effects, nozzle clogging, and difficulties in controlling film thickness and homogeneity across large areas. Addressing these challenges requires innovations in ink formulations, printing protocols, and the design of advanced hardware.

Additionally, sustainable strategies are examined, including the use of lead-free perovskites and eco-friendly solvents, which aim to reduce environmental impact while maintaining device performance. Examples of recent advancements are presented, such as fully inkjet-printed devices integrating all functional layers, which demonstrate the scalability and versatility of the technique. Future perspectives focus on the integration of inkjet printing into roll-to-roll manufacturing systems, enabling large-scale, cost-effective production of PeLEDs. These developments could unlock new opportunities for commercial applications, including flexible displays, wearable electronics, and next-generation lighting systems.

The demand for sustainable and efficient optoelectronic materials has led to significant interest in lead-free halide perovskites. Among these, CsCu₂I₃, a one-dimensional copper-based halide perovskite, has emerged as a promising material due to its excellent optoelectronic properties, high stability, and non-toxic composition. CsCu₂I₃ exhibits strong quantum confinement and broad absorption in the ultraviolet (UV) region, making it suitable for applications in photodetectors. Its self-trapped exciton (STE) emission mechanism ensures a high photoluminescence quantum yield in the visible range and substantial Stokes shift, critical for UV detection. [1], [2]

In this study, CsCu₂I₃ was processed into thin films using an environmentally friendly inkjet printing method. A stable precursor ink was synthesized by dissolving CsI and CuI in dimethyl sulfoxide (DMSO) at a 1:2 molar ratio to obtain a 0.5 M solution. Films were printed onto ozone-treated ITO-patterned glass substrates with interdigitated electrodes at varying distances (50–200 µm) in order to define our photoconductor, with a thickness about 50 nm. Inkjet printing parameters such as drop spacing and platen temperature were optimized to produce high-quality and uniform films. The printed films were annealed at 100 °C under vacuum to enhance their crystallinity and stability.

The fabricated photoconductors were characterized both optically and electrically. Transmittance and reflectance measurements of thin films revealed an absorption edge at E_g = 3.75 eV, i.e., wavelengths shorter than 330 nm are efficiently absorbed. Electrical measurements, including current-voltage and current-time responses under illumination across the 280–500 nm range, confirmed the significant photodetection capabilities of our photoconductors in the UV region (see Figure), with responsivities above 0.1 A/W at wavelengths below 300 nm at 5 V. These results position inkjet-printed CsCu₂I₃ as a versatile, lead-free material for the next generation of UV photodetectors. This work highlights the potential of scalable, low-cost manufacturing techniques for eco-friendly photonic applications.

Metal halide perovskites are emerging as promising semiconductors for cost-effective and high-performance optoelectronic devices. Tremendous research attention has been attracted to perovskite layers, however, an in-depth understanding of how the buried charge transport layers affect the perovskite crystallization, compositions and film quality, though of critical importance, is currently unclear.

Here, we firstly, systematically studied synergy effects between perovskite precursor stoichiometry and interfacial reactions for high-performance perovskite LEDs (PeLEDs) and establish useful guidelines for rational device optimization. We reveal that efficient deprotonation of the undesirable organic cations by a metal oxide interlayer with a high isoelectric point is critical to promote the transition of intermediate phases to highly emissive perovskite films.^[1] We further reveal that the deprotonation of FA+ cations and the formation of hydrogen-bonded gels consisting of CsI and FA facilitated by zinc oxide underneath, effectively removes the Cs-FA ion-exchange barrier, promoting the formation of phase-pure CsxFA1-xPbI3 films with emission filling the gap between that of pure Cs- and FA-based perovskites.Based on this discovery, we successfully fabricated a set of highly emissive Cs_xFA_1-xPbI₃ perovskite films with fine-tuning Cs-FA alloying ratio for emission-tuneable near-infrared light-emitting diodes (NIR-LEDs).^[2]

We further developed a multifunctional display using highly photo-responsive metal halide PeLEDs as pixels following works mentioned above. by careful control of the interfacial reactions, we achieved  strong photo response of the PeLED pixels. Therefore, the display can be simultaneously used as touch screen, fingerprint sensor, ambient light sensor, and image sensor without integrating any additional sensors. In addition, decent light-to-electricity conversion efficiency of the pixels also enables the display to act as a photovoltaic device to charge the equipment.^[3] The multiple-functions of our PeLED pixels can not only simplify the display module structure and realize ultra-thin and light-weight display, but also significantly enhance the user experience by these advanced new applications. As such, our results demonstrate great potential of PeLEDs for a new generation of displays for future electronic devices.

Low-dimensional metal halide perovskites are attracting great interest for photovoltaics and photonics. In particular, 2D tin perovskites have been shown to have good optical gain properties which make them promising for applications as coherent light sources. [1] On the other hand, the ability of lead-based 2D perovskites to sustain lasing remain highly controversial. [2]  Here we show that both Sn and Pb-based 2D perovskites thin films can achieve amplified stimulated emission, and compare their properties as function of the optical pumping conditions as well as of the materials’ structural characteristics. By employing ¹H, ¹³C, ¹⁵N, ¹¹⁹Sn and ²⁰⁷Pb solid state NMR spectroscopy, we were able to discern the local structural environments of the 2D perovskite of interest through their characteristic spectral fingerprints. Spin relaxation dynamics measurements reveal that the local supramolecular spatial arrangements, the molecular motions and structural rigidity are key factors shaping the energetic landscape of the material and its luminescence properties. Our work provides a deeper understanding of the structure-properties relationship of these soft semiconductors to assist the rational engineering of materials with improved optical properties for lasing applications.

The study on lead halide perovskite nanocrystal (LHP NC) light-emitting diodes (LEDs), despite their recent existence, has seen a substantial progress in the research community. With their significantly increased surface area, passivation of surface with appropriate ligands is crucial. While advances in stability and optical properties are outstanding, the electrical accessibility of NCs has gained less attention so far. Specifically, efficient electroluminescence in LEDs rely on a thorough comprehension of the influence of charge carrier injection into the emitting material¹.

In this study, we investigate commercial cubic CsPbBr₃ NCs passivated with oleyl amine/oleic acid (OLA/OA) and ligand-exchanged NCs with didodecyldimethylammonium bromide (DDABr). It is known that long capping ligands impede carrier injection, making them ineffective in LED fabrication². Transmission electron microscopy (TEM) images after ligand exchange show a reduction in interparticle distance along with nuclear magnetic resonance (NMR) spectroscopy indicating minimal ligand coverage on ligand-exchanged particles. Improved carrier balance is observed in DDABr capped NCs and photoelectron spectroscopy reveals a reduction in hole injection barrier. Resulting LEDs fabricated with ligand exchanged NCs exhibit a higher and almost constant external quantum efficiency (EQE) at high current densities, indicating a better carrier balance³. Density functional theory (DFT) studies reveal the occurrence of trap states with excess OLA⁴, whereas a favorable bandgap shift is expected with DDABr capped NCs. These results suggest that the issue of LHP NCs in PeLED fabrication is not just the long insulating ligands alone; ligand coverage and the type of anchoring group is important as well. Thus, a deeper understanding of the interaction of the ligand attached on the NC surface is required.