Angelica Simbula

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.

Halide perovskites have enabled major advances in optoelectronics, extending well beyond photovoltaics. Their mixed ionic‐electronic conduction, once regarded as detrimental to device stability, is increasingly viewed as a functional degree of freedom for memory and neuromorphic‐inspired devices, especially when coupled to external stimuli such as light. Specifically, single crystals are attractive models because they suppress grain‐boundary effects and microstructural disorder that can mask intrinsic transport and interfacial mechanisms in polycrystalline films. Here, we report the growth of thin methylammonium lead iodide (MAPbI ₃ ) single crystals by a space‐confined method and their integration into planar two‐terminal devices with directly deposited Ag contacts. At room temperature, the devices exhibit ultra‐low dark currents (10 ⁻¹³ ‐10 ⁻¹² A) and negligible hysteresis in the dark. Under illumination, the current increases due to photogeneration and the I‐V characteristics develop a pronounced polarity‐dependent hysteresis and a threshold‐like transition between two conductance states. Temperature‐dependent dark measurements (300–400 K) show thermionically activated, contact‐influenced transport and a weakly varying normalized hysteresis metric. Together with the back‐to‐back Schottky‐diode analysis and control devices using more inert contact materials, these results support a transport model in which Ag/perovskite interfaces play a central role and the hysteretic response is influenced by coupled interfacial and ionic processes.

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.

Conjugation of low‐cost and high‐performance semiconductors is essential in solar‐driven photoelectrochemical (PEC) energy conversion. Sb₂S₃ is a wide‐bandgap (≈1.7 eV) semiconductor with the potential to deliver a maximum photocurrent density of 24.5 mA cm⁻², making it highly attractive for PEC water splitting applications. However, bulk Sb₂S₃ exhibits intrinsic recombination issues and low electron–hole separation, posing a limit to photocurrent generation. This study clarifies the carrier dynamics by ultrafast spectroscopy measurements and proposes the design of a heterojunction between Sb₂S₃ and SnO₂, with suitable band‐edge energy offset. The SnO₂/Sb₂S₃ heterojunction enhances the charge separation efficiency, resulting in improvement of the photocurrent. The SnO₂/Sb₂S₃ photoanode, fabricated entirely by vapor deposition processes, demonstrates photoelectrochemical water oxidation with a photocurrent density up to ≈3 mA cm⁻² at 1.38 V versus RHE.

We study amplified spontaneous emission (ASE) in MAPbBr₃ planar waveguides using femtosecond spectroscopy. We show that ASE happens without optical gain, and involves exciton-polaritons at low excitations and new hybrid states at high excitations.

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.

By combining Er^III and Yb^III ions with 3,6-dithiophene-anilate (Th₂An) and scorpionate hydrotris(pyrazol-1-yl)borate (HBpz₃⁻) ligands new luminescent dinuclear complexes are obtained. The two materials formulated as [((HB(pz)₃)₂Yb)₂(μ-th₂An)]·4DCM·1.3H₂O 1Yb and [((HB(pz)₃)₂Er)₂(μ-th₂An)]·4DCM·1.8H₂O 1Er, respectively, have been structurally characterized by SC-XRD and PXRD studies. This study presents a comprehensive investigation of the photophysical properties of the Th₂An ligand for the first time. Our findings reveal the crucial role of the thiophene anilate as an effective optical antenna, which sensitizes near-infrared (NIR)-emitting lanthanide ions, specifically Er^III and Yb^III. The significant impact of vibrational quenching on the Ln^III NIR emission efficiency has been also highlighted.

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.

Designing innovative photocatalysts for nitrogen photofixation is becoming crucial for the development of carbon neutral ammonia production. Metal halide perovskites (MHPs) have been demonstrated to be effective materials to run a wide range of photoredox reactions mediated by solar light. Herein, we develop an innovative heterojunction based on the vacancy-ordered double perovskite Cs2SnBr6 and carbon nitride nanosheets and demonstrate its ability in running the nitrogen photofixation reaction to produce ammonia. We explore the full compositional range for the Cs2SnBr6/g-C3N4 system and identify an optimal range providing an ammonia evolution rate up to 260 μmol g-1 h-1, the highest value reported to date for a MHP-containing catalyst. Mechanistic insight into the photofixation reaction promoted by the heterojunction was obtained through a combination of advanced spectroscopy and computational modelling. Efficient ammonia production stems from an effective charge transfer from the perovskite to the nitrogen vacancies on the carbon nitride enabled by the absence of self-trapped excitons in Cs2SnBr6 which also provides additional reactive sites through bromide vacancies. This work, reporting an efficient MHP-based heterojunction for nitrogen photofixation and a clear definition of the underlying reaction mechanism, provides a catalyst design strategy that may pave the way for sustainable ammonia production.