Efficiency of one junction perovskite solar cells has almost reached the theoretical limit, and tandem devices are the possible solution to surpass it. To fabricate all perovskite tandem solar cells, it is required to have efficient and stable wide bandgap absorbing material as a top cell. Mixed-halide MAPbBr2I perovskite has bandgap of 2 eV, which makes this material a perfect pair to conventional MAPbI3 in two junction tandem solar cell. However, this anion composition is highly sensitive to ion migration, which significantly limits the photostability of fabricated devices. Under external influences ions start to migrate across the device, which leads to Hoke and Schottky effects, and consequent efficiency losses during sun exposure. In this work we investigate the effect of incorporation of cesium as additional cation in MAPbBr2I perovskite composition. We demonstrate that 20% of Cs leads to significantly improved photostability of the films and devices due to ion migration reduction, which was found from impedance spectroscopy and capacitance measurements of the samples. The shift of photoluminescence peak position under light soaking was ten times lower for MA0.8Cs0.2PbBr2I, and T80 time increased up to 38 times, showing significant decreased only after storing the devices for 1500 h.

Ion migration in halide perovskites is a key factor limiting the operational stability of solar cells due to formation of halogen ion enriched domains and accumulation layers. The present work demonstrates the manifestation of ion migration in two ways via Hoke and Schottky effects. Both effects are induced by external exposure but they have a peculiar way of solar cell performance degradation. We demonstrate the effects of ion migration on the device performance by measuring time dependent short-circuit current and different impedance characteristics that allow to see how charge-carrier separation property degrades. The Schottky effect leads to the rapid (<1 min) decrease of charge-carrier separation characteristic of solar cell while Hoke effect leads to the slow (>10 min) defect accumulation in the perovskite layer leading to the enhanced Shockley-Read-Hall recombination. Separation of these two effects can be realized by simple increase of transport layer thickness. A thick transport layer blocks losses of charge-carrier selectivity in a solar cell and leads to an enormous increase of T80 time of short circuit current, from 15 s up to 60 min.

The explosive development of halide perovskite optoelectronics exposed the need for development of simple optical methods capable of fast material quality assessment and control, yielding a deep understanding of charge-carrier recombination processes. Optoelectronic devices work in the widest range of charge-carrier concentrations, from relatively low concentrations for photodiodes and solar cells (i.e., < 1016 cm-3) up to high concentrations for light-emitting diodes (i.e., < 1017 cm-3) and even extreme situations like lasers (i.e., < 1018 cm-3). For the realization of high-throughput perovskite laser fabrication methods the contributions of structure and passivation on recombination mechanisms must be considered. Here we propose a simple optical approach for perovskite laser media characterization, which can serve as a figure of merit for the evaluation of the amplified spontaneous emission capability. Our approach is based on the interconnection of standard optical measurements of photoluminescence quantum yield and time-resolved spectroscopy with slight modifications that allow the direct observation recombination mechanisms evolution and buildup of Auger recombination. The application of our approach to various species of CsPbBr3-based perovskite samples - quantum dots, bulk and polymer-perovskite composites - demonstrates a straightforward difference in charge-carrier dynamics allowing fine selection of optimal material for the fabrication of perovskite microlasers.

Incoherent light is one of the most common and widely used types of radiation in the modern world. Its main advantages include a broad wavelength range, the simplicity of creating sources for such radiation, and high energy efficiency. However, its primary drawback is the lack of coherence and, consequently, the inability to use standard methods for controlling the wavefront of such radiation, which limits the application scope of incoherent light sources. In this work, we developed and investigated a unified system comprising a perovskite (as the incoherent light source) and diffractive optical elements for manipulating the photoluminescence wavefront. We demonstrated the focusing of perovskite photoluminescence using an amplitude Fresnel zone plate. Furthermore, we showed the possibility of generating a simplest hologram, specifically by demonstrating the generation of an optical vortex via a pitch-fork grating.

Transparent polymers are low-cost, light, and flexible, making them prospective for a plethora of applications. Still, their usage in photonics is impeded by a low refractive index, usually less than 1.7. In this work, an alternative strategy is proposed for improving optical characteristics by developing poly(ionic liquids) (PILs) with a gradient refractive index (GRIN) in thin films. The obtained PILs are transparent, environmentally friendly, and possess the GRIN effect in thin films. Inspired by the architecture of the animal's eye, PILs are employed for inkjet fabrication of microlenses with a giant GRIN value of 0.8, which is up to several times higher than that in previous studies on nanolayered polymeric and 3D printed GRIN lenses. Furthermore, in terms of focusing power, lens transparency, and depth of field, these microlenses outperform the result of high refractive index polymers. Hence, the findings open a novel platform for compact optical components based on new types of ionic polymers.

The ability to control the emissive properties of materials is one of the main challenges in modern active photonics. Reversible control of the radiation intensity would open new opportunities for the development of photonic computing, neuromorphic optical circuits, micro anti-counterfeit tags, and others. To achieve such control, a hybrid GST-perovskite platform was previously proposed; however, due to a high concentration of defects in GST, this platform had a low radiation efficiency. Here, we study the possibility of shielding the perovskite from the GST layer while maintaining control of the perovskite emission intensity by switching the GST phase. Using a thin layer of MgO dielectric in the GST-perovskite platform, we have obtained 3.5 times increase in the intensity. Moreover, we have increased the emission lifetime of the perovskite, which also indicates a successful passivation of defects in GST.

As alternatives to conventional perovskite light-emitting diodes, perovskite light-emitting electrochemical cells (PeLECs) are in great demand in modern science and technology due to their simplified structure and attainable higher luminance. Here, for the first time, we present the implementation and characterization of red CsPbIBr2-based PeLECs/LEDs. To improve perovskite material phase stability, we applied the following strategies for mitigating the mixed anion lead halide perovskite phase segregation: Pb2+ partial substitution by Mn2+, boundary passivation by poly(ethylene oxide) with polyvinylidene fluoride, and two-step thermal treatment with vacuuming and annealing. The complex measurements of photoluminescence, optical density, energy-dispersive X-ray spectroscopy, and X-ray diffraction confirm the minor phase segregation in the optimized perovskite layers. The performed ab-initio calculations predicted the band gaps of perovskite materials with a mixed anion composition, corresponding well to the results of optical measurements. Finally, current and electroluminescence time tracking proved the formation of a dynamic p-i-n structure in the studied PeLEC devices. The developed PeLECs/LEDs exhibited relatively high, for red PeLECs, electroluminescence up to 96 cd m-2 with a peak position at 667-672 nm.

In this manuscript, we present a study on the optical properties of ZnO NWs and microcrystals synthesized via hydrothermal method. The NWs were characterized by low-temperature photoluminescence spectroscopy, which revealed resonance modes indicating random lasing behavior mediated by scattering from misoriented nanowires. The spectral position of the resonance modes suggests lasing in the P-band region of exciton–exciton interaction. Our results also indicate a correlation between the surface density of nanostructures and the peak emission intensity. In addition, optically behavior of individual ZnO microprisms integrated in with a thin perovskite active layer were investigated by room-temperature microphotoluminescence spectroscopy. The results indicate that the ZnO microprisms are efficient optical cavities. Overall, our findings demonstrate the potential of hydrothermal synthesis for the fabrication of efficient ZnO-based light-emitting devices.

Direct bandgap semiconductors possess a unique attribute: the presence of a free exciton state with a high total oscillator strength. This property makes them highly promising for applications in ultrafast optical signal processing and optical computing. One such protocol for optical computing is based on four-wave mixing (FWM). In this study, the nonlinear optical effect in polycrystalline thin films of halide perovskite MAPbI(3) (MA(+) = CH3NH3+) at low temperatures is demonstrated. Through analyzing the spectroscopy of the FWM signal, studying the photoluminescence excitation spectra, and comparing the findings with results from MAPbI3 single crystals, it has been discovered that the strongest nonlinear response is observed at the free exciton resonance and in the region of shallow defect states. Surprisingly, the presence of FWM in cross-linear excitation geometry has been observed, indicating potential involvement of other nonlinear or many-body effects. The observations of FWM with free excitons even in highly defective MAPbI3 thin films demonstrate the robustness of the exciton resonance and highlight the practical prospects for utilizing this material in optical computing.

Three-dimensional (3D) photonic structure made of light-emitting materials is a prospective platform for designing lasers and 3D displays, where directivity and efficiency of the emission are highly demanded. While the fabrication of two-dimensional (2D) light-emitting photonic structures is a well-developed technology, the extension of dimensionality up to 3D requires complex and multistep approaches. In this regard, solution-processible halide perovskites are promising materials, which can be easily integrated with various scaffolds supporting optical modes. Here we demonstrate a novel simple two-step technique for fabrication of halide perovskite-based light-emitting 2D and 3D photonic structures based on femtosecond laser photopolymerization and further perovskite growth inside the structures. High defect tolerance of halide perovskites supports synthesis of high-quality material inside the photonic structures, which demonstrate amplified spontaneous emission and stable laser generation. Moreover, we show that the developed method is rather universal and allows for the successful fabrication of photonic structures filled by the various halide perovskites like all-inorganic, organic-inorganic, bromide, and chlorine ones.

Halide perovskite light-emitting electrochemical cells are a novel type of the perovskite optoelectronic devices that differs from the perovskite light-emitting diodes by a simple monolayered architecture. Here, we develop a perovskite electrochemical cell both for light emission and detection, where the active layer consists of a composite material made of halide perovskite microcrystals, polymer support matrix, and added mobile ions. The perovskite electrochemical cell of CsPbBr3:PEO:LiTFSI composition, emitting light at the wavelength of 523 nm, yields the luminance more than 7000 cd/m2 and electroluminescence efficiency of 1.3×105 lm/W. The device fabricated on a silicon substrate with transparent single-walled carbon nanotube film as a top contact exhibits 40% lower Joule heating compared to the perovskite optoelectronic devices fabricated on conventional ITO/glass substrates. Moreover, the device operates as a photodetector with a sensitivity up to 0.75 A/W, specific detectivity of 8.56×1011 Jones, and linear dynamic range of 48 dB. The technological potential of such a device is proven by demonstration of 24-pixel indicator display as well as by successful device miniaturization by creation of electroluminescent images with the smallest features less than 50 μm.

Multiwall carbon nanotubes can be used for development of semitransparent light-emitting electrochemical cells. Due to its chemical inertness, they can withstand highly corrosive materials like halide perovskites, which are the most promising material for fabrication of next generation optoelectronic devices. Here we investigate how perovskite-based light-emitting electrochemical cell can be fabricated only with carbon nanotubes as anode and cathode. We show that for the fabrication drop-casting technique should be used instead of conventional spin-coating method. High roughness of the multiwall carbon nanotubes can be overcome with drop casting method of material deposition that allows fabrication of thick films. Light-emitting electrochemical cells demonstrate relatively low maximum luminance of 50 cd/m2 and we demonstrate the issue behind it.

The spectral-luminescent properties of new composite materials based on porous matrices of photo-thermo-refractive glasses with a silver ion-exchange layer and CsPbBr3 inorganic perovskite nanocrystals have been studied. Perovskite nanocrystals were introduced into a porous matrix by the method of pumping solutions through a sample under piston pressure. Two mechanisms of interaction between silver nanoparticles and perovskite nanocrystals have been revealed, such as enhancement of the local field and luminescence quenching due to the high absorption of nanoparticles. The quantum yield of the studied samples under different irradiation associated with an increase in the concentration of silver nanoparticles was 34% without irradiation, 51% with 100 j irradiation dose, and 25% with 1000 j irradiation dose. In this case, an increase in the integrated luminescence intensity was observed in glasses irradiated with 100 J by a factor of 2.97 and irradiated with 1000 J by a factor of 1.76 compared to the unirradiated sample. The average luminescence lifetime decreases from 2.19 to 1.68 ns with an increase in the concentration of nanoparticles.

Mixed halide perovskites undergo phase segregation, manifested as spectral red-shifting of photoluminescence spectra under illumination. In the iodine-bromide mixed perovskites, the origin of the low-energy luminescence is related to iodine-enriched domains formation. Such domains create favorable bands for the induced carrier funneling into them. Despite the phase segregation process is crucial for mixed halide perovskite-based optoelectronics, numerous gaps exist within the understanding of this phenomenon. One such gap pertains to the emergence of temporary and intermediate photoluminescence peaks during the initial stages of phase segregation. However, these peaks appear only within the first few seconds of illumination. Nevertheless, the decreasing temperature may prolong these initial stages. In this work, we carry out a detailed study of the temperature dependence of anion segregation in MAPbBr_2I and MAPbBr2.5I0.5 halide perovskites, to obtain a deeper comprehension of segregation processes, particularly during their initial stages. The temporal evolution of low-temperature photoluminescence reveals the undergoing of the intermediate stage during the segregation process and temperature-related phase transition from orthorhombic to tetragonal phase. To complement the phase segregation study, the temperature dependence of time-resolved photoluminescence spectroscopy is provided, allowing us to estimate the change in the photoluminescence lifetimes for the initial and segregated peaks with temperature.

Carbon dots (CDs) emerge as a novel type of fluorescent materials with a good photostability, biocompatibility, and high quantum yield. They become a promising alternative to conventional fluorescent materials such as rare‐earth phosphors and semiconductor quantum dots owing to their ease of synthesis and fabrication from ready‐available compounds. Near‐infrared (NIR) CDs are of high demand for in vivo studies owing to little photoinduced damage to surrounding tissues, deep penetration of radiation into tissue, and low autofluorescence. A laser‐assisted synthesis approach is demonstrated, which allows NIR‐emitting CDs to be obtained. By rapidly heating the precursors (4,4’‐bis(diethylamino)benzophenone in sol–gel matrix) with femtosecond pulses, NIR emitting CDs can be obtained with the emission in the ranges of 800–1000 and 1100–1600 nm of the resulting CDs.

This article shows the new insights for stabilizing the p‐i‐n perovskite solar cells (PSCs) and modules based on double cation CsFAPbI3 absorber using CsCl additives. The presence of chlorine in the perovskite crystal structure results in the decrease of the lattice parameters by 0.6 ± 0.06%, in the increase of the bandgap value (+0.018 eV), and charge carrier lifetimes with respect to the undoped one. The champion PSCs based on the CsFAPbI3−xClx absorber show an increase in power conversation efficiency from 18.06% up to 20.13% after Cl doping. The light‐soaking stability of PSCs measured at maximum power point demonstrates impressive increase of the T80 from 1128 h for CsFAPbI3‐based devices to more than 3479 h for CsFAPbI3−xClx ones. It is found that the Cl doping suppresses the formation of lead iodide and pure CsPbI3 induced by decomposition and phase segregation processes only when the perovskite is covered with the C60/BCP electron‐transporting layer (ETL), while in the structure without ETL Cl additive is not effective. Finally, the high potential of Cl‐anion engineering for the perovskite modules (5 × 5 cm2) is demonstrated, which shows promising 17.08% of power conversation efficiency and light‐soaking stability for 1396 h.

Halide perovskites are a class of semiconductors with strong direct interband transition and high mobility of charge carriers resulting in bright luminescence, which can be easily tuned chemically in a broad spectral range. Moreover, perovskites can be synthesized by means of simple wet chemistry approaches on arbitrary surfaces, opening new avenues for perovskites integration with a plethora of other functional materials. Here, this work reports on a versatile platform for reversible switching of halide perovskite's optical properties enabled by high-index phase-change materials (Ge-Sb-Te) serving as an active subnanolayer, which controls the perovskite film's behavior. Based on this approach, this work demonstrates micro-QR-coding and switchable bright emission, whose wavelength can be adjusted in the whole visible range.

Halide perovskite light-emitting electrochemical cells (LEC) are color-tunable, efficient, simple, and low-cost single-layer devices, which can be designed in semitransparent architectures for various lightening and display. However, development of highly transparent and conductive electrodes for these devices is a challenging task, requiring not only optimization of the electrode material parameters, but also stable performance without chemical reactions at interfaces. Here we employ multi-walled carbon nanotubes with substantially improved optical and transport properties after their additional chemical processing for efficient semitransparent perovskite LEC. In particular, we develop single-layer perovskite-based LECs with transparency 56%, brightness up to 1625 cd/m2 and maximum current efficiency 3.6 cd/A. We believe that our low-cost and efficient devices would be suitable for semitransparent display technologies.

Up-conversion is a process that can be used for infrared laser visualization. Lead halide perovskite has a fine opportunity to be employed for up-conversion. Halide perovskite has not only good photovoltaic and optoelectronic properties but also good photonic properties. Simple chemical fabrication methods and unique properties make perovskites cheap and attractive materials for different applications. In this article, we show different perovskite structures that possess up-conversion of near-infrared laser emission to visible green light.