Michele Saba

Hybrid organic‐inorganic halide perovskites are attractive semiconductors for optoelectronics, but their electrical and photoresponse are often affected by slow ion‐mediated processes. Although ion migration and history‐dependent photoresponse are well established in halide perovskites, how these mixed ionic‐electronic effects depend on device architecture remains unclear. Here, we investigate solution‐grown MAPbBr ₃ microwires integrated onto interdigitated Au electrodes in two representative configurations: a single‐gap (SG) device and a multi‐gap (MG) device comprising five parallel electrically active regions. Combining dark and illuminated current‐voltage measurements, SCLC analysis, and time‐resolved photocurrent measurements under pulsed broadband illumination, we reveal markedly different hysteretic and transient behaviors in the two contact configurations. The SG device exhibits pronounced illumination‐history‐dependent transients and strongly power‐dependent transport, consistent with a significant contribution from local ionic polarization, trap‐mediated processes, and contact injection. In contrast, the MG device displays a more stable and weakly power‐dependent photoresponse. A phenomenological parallel‐channel model shows that the measured polarization‐induced voltage offset in a multi‐gap architecture can be expressed as a conductance‐weighted contribution of the local polarization potentials associated with the individual electrically active regions. These results provide an architecture‐dependent framework for understanding how contact configuration modulates mixed ionic–electronic transport and hysteresis in MAPbBr3 microwire devices.

The defect tolerance of metal halide perovskites endows them with ambipolar transport and outstanding optoelectronic properties, yet it simultaneously inhibits intentional, controlled doping that is essential for directional charge flow in advanced optoelectronic devices. The limited strategies available to tune the electron–hole balance typically involve deep defect states and associated non‐radiative recombination that degrades the open‐circuit voltage of solar cells. Here, we incorporate chlorine‐terminate MXenes (Ti ₃ C ₂ Cl ₂ ) into wide‐bandgap perovskite solar cells to exploit bimolecular recombination and engineer photodoping mechanisms, without sacrificing solar cell performance. In fact, compared to reference cells, MXene‐modified devices show simultaneous improvements of V _OC , J _SC , and fill factor, resulting in a 10% power conversion efficiency enhancement up to 18%. Ultrafast optical spectroscopy, through joint time‐resolved photoluminescence and transient absorption, quantifies the imbalance between electron and hole populations under illumination. Density functional theory calculations indicate that perovskite–MXene heterojunctions create trap states for hole capture, resulting in a prolonged lifetime of free electrons because of the generalized mass‐action law. This work demonstrates photodoping in perovskites through the use of MXenes and opens a promising pathway for directional transport, with implications not only for solar cell performance, but also for novel optoelectronic applications requiring intentional doping.

CsPbBr ₃ nanocrystals (CPB NCs), an all‐inorganic halide perovskite, have demonstrated high efficiency and significant commercialization potential in fields such as light‐emitting diodes, solar cells, photodetectors, lasers, and bioimaging. However, the instability of CPB NCs in ambient environments remains a major challenge that must be addressed before their widespread commercial applications. Core–shell structural engineering of CPB NCs has been widely employed to mitigate the impacts of external environmental factors, significantly enhancing long‐term stability against moisture, thermal, and oxygen. A protective shell layer covering CPB NCs prevents direct exposure to these environmental factors, providing excellent stability. This review summarizes recent advancements and challenges in CPB NCs‐based core–shell materials, systematically analyzing how shell material types and bandgap structures influence luminescence stability. The energy band structure and configuration of CPB NCs‐shell are discussed in detail, and the classification of shell types, such as perovskite and its derivatives, oxide shells, and polymer shells in single‐layer configurations, is reviewed. Special attention is given to the applications of the CPB NCs‐based core–shell materials with enhanced stability. Finally, the main challenges and further research directions for the core–shell structure of CPB NCs are discussed, with the aim of promoting the development of stable metal halide perovskite materials in the future.

Tin‐based perovskites offer one of the most viable sustainable alternatives to their lead counterparts, combining comparable band structures with strong visible‐light absorption and favorable charge transport. Most studies have focused on thin films, where grain boundaries dominate charge transport, and the large surface area accelerates the oxidation of tin, obscuring the intrinsic properties of the material. Here, single crystals of phenethylammonium tin iodide (PEA ₂ SnI ₄ ) are investigated, isolating their fundamental optoelectronic response from film‐related artefacts. It is found that air and light exposure primarily affect surface layers, with partial recovery achievable through exfoliation. Photodetectors fabricated from single crystals exhibit a photoresponsivity of ≈60 A W ⁻¹ under low‐intensity 650 nm illumination, with photocurrent scaling quadratically with bias in a space charge‐limited current regime, and transport displaying a transition from thermal excitation to phonon scattering at 225 K. Time‐resolved photocurrent measurements further reveal prolonged decay dynamics and cumulative pulse responses, characteristic of short‐term synaptic plasticity such as temporal integration and voltage‐modulated persistence. These findings establish PEA ₂ SnI ₄ single crystals as a benchmark for understanding degradation and transport in lead‐free perovskites, while positioning them as a viable materials platform for neuromorphic vision and adaptive optoelectronics.

Single-crystal metal-halide perovskites hold significant promise for optoelectronic applications due to their tunable physical properties and the possibility of low-cost, low-temperature synthesis. Compared to their polycrystalline counterparts, they exhibit reduced defect densities and enhanced stability. Their intrinsically soft lattice facilitates integration with conventional semiconductors via heterostructures. However, their high ionic mobility can lead to interdiffusion processes that compromise the integrity of adjacent layers, making the formation of well-defined interfaces a critical challenge for device optimization. Here, we exploit the temperature dependence of the perovskite growth kinetics to demonstrate a one-pot, space-confined growth method for synthesizing vertical 2D/3D lead-halide perovskite heterostructures in single-crystal form. The process leverages differences in precursor solubility to drive sequential crystallization and create well-defined interfaces. Structural and optical analyses confirm the formation of stable, phase-separated heterostructures, which are promising for optoelectronic applications.

CuI as a hole transport layer was deposited from a solution for the fabrication of methylammonium (MA)-free half Sn-half Pb perovskite solar cells with a power conversion efficiency of over 20% and enhanced stability.

Zero-dimensional perovskites have received intensive attention due to their low formation energy and soft ionic nature. Although thermochromism has been observed in perovskite materials, little is known about the effects of A-site cations and exciton-phonon coupling on the color-switching mechanism. Here, thermochromism in a composite perovskite where CsPbBr₃ nanocrystals are embedded in a matrix of Cs₄PbBr₆ microcrystals has been reported. Reversible color switching occurs with a progressive change from yellow-green to orange in a wide temperature range of 295-495 K. It is found that the temperature-induced bandgap change can be attributed to the competing interaction between lattice thermal expansion and electron-phonon interaction. The entire heating and cooling process is accompanied by the movement of Cs⁺ and distortion of the [PbBr₆]^4- octahedron, while the former is more drastic through temperature-dependent Raman spectra and verified by Materials Studio calculations. The cation dynamics have been investigated, at the atomic scale, by using molecular dynamics simulations, which indicate Cs⁺ has more freedom to move in the lattice. This work provides insights to guide strategies for designing a material platform for diverse optical anticounterfeiting and temperature-indicating label applications and describes the emission color tuning mechanisms for further design of stimuli-responsive materials.

Metal halide perovskites have emerged as promising materials for low‐threshold lasers, ideally suited for integrated optical circuits due to their easy fabrication, tunable wavelength, and seamless on‐chip integration. Exciton lasing, electron‐hole population inversion, polariton condensation and superfluorescence have been proposed to explain the low threshold. Fundamental to discriminate lasing mechanisms is the knowledge of the material's absorption/gain spectrum in the stimulated emission regime, a difficult experimental task in microcavities and metasurfaces. In this study, femtosecond tandem spectroscopy applied to MAPbBr₃ planar waveguides enables the measurement of material absorption and gain spectra at any carrier density, as well as directly monitoring the matter component of hybrid excitations. Results demonstrate that stimulated emission always involves hybrid electron‐hole‐photon excitations in the absence of photon gain, even at the highest excitations when the exciton resonance is completely bleached, a characteristic almost unique in the landscape of photonic materials. Parameter‐free numerical simulations show that MAPbBr₃ waveguides support electromagnetic modes with an exciton‐polariton‐like dispersion below the bandgap at all investigated carrier densities. These excitations combine the advantages of hybrid light‐matter states‐ namely, lower stimulated emission thresholds and higher nonlinearities‐ with the robustness of photon amplification, seamlessly extending potential applications from low to high carrier densities.

Single‐crystal hybrid perovskites represent an emerging class of next‐generation semiconductors due to their excellent and tunable optoelectronic properties, along with a solution‐based, low‐temperature growth process. 2D single‐crystal hybrid perovskites are especially promising as their long‐range ordered multiple quantum well structure induces many peculiar properties, such as large exciton binding energy, large in‐plane conductivity, and improved environmental stability, which make them suitable for low‐dimensional optoelectronics applications and fundamental studies. Herein, the structural properties, morphology, and optoelectronic behavior of 2D thin film phenethylammonium lead iodide (PEA ₂ PbI ₄ ) single‐crystals, synthesized using the space‐confined growth technique are explored. A planar device is fabricated and its spectral photoresponse is studied under broadband supercontinuum white light. Remarkably, the device exhibits an ultra‐low dark current (10 ⁻¹⁴ A), indicative of low defect density and suppressed ion migration. Under white light, the current increases linearly with the incident power, up to a factor of 10 ⁵ , and the device achieves a specific detectivity of 10 ⁹ Jones. The temperature and wavelength dependence of the photocurrent suggests the dissociation of excitons as one of the main mechanisms affecting photoconduction. Furthermore, stability under air exposure and illumination turns out to be remarkable.