The evolution of inkjet-printed electronics has opened transformative pathways for intelligent sensing platforms that seamlessly integrate photonic detection with in-memory computing. This work presents a holistic approach to scalable optoelectronics, bridging the gap between robust logic-in-memory architectures and optically tunable synaptic plasticity for next-generation biosensors.

Our work began with the development of fully inkjet-printed metal-insulator-metal (MIM) structures using high-k HfO₂ dielectrics. These devices demonstrated low-power, non-volatile switching, strong retention, and uniformity suitable for passive memory and selector applications, establishing a scalable platform for printed memory arrays. Building upon this, we transitioned to 2D materials, particularly hexagonal boron nitride (h-BN), achieving devices with high endurance, reproducibility, and tolerance to stochastic variation. Establishing the computational backend, we first demonstrate fully inkjet-printed hexagonal boron nitride (h-BN) memristors capable of current-controlled stateful MAGIC logic as h-BN used for thee logic-in-memory. By utilizing the volatile and non-volatile resistive switching behaviors of Ag/h-BN/Au structures, we achieved high endurance (up to 250,000 cycles) and improved input stability for NOR gate operations. This provides the necessary logic density for processing sensor data directly in memory without the Von Neumann bottleneck.

This foundation set the stage for the next leap: the integration of halide perovskites as multifunctional active layers. Leveraging the photoelectric tunability of Sn-based and CsPbBr₃ nanocrystal perovskites, we demonstrated a new generation of printed devices capable of modulating light in response to electrical and optical history. In particular, TEA₂SnI₄, PEA₂SnI₄, and FASnI₃-based devices were inkjet-patterned within vertical cavity and multilayer structures to exhibit persistent photoconductivity, state-dependent photoluminescence, and feedback-tunable random lasing—hallmarks of optical memristors and photonic synapses.

Bridging the gap between logic and light, we investigated the memristive properties of CsPbBr₃ perovskite devices within a p-i-n diode architecture (PEDOT:PSS/NiO/CsPbBr₃/SnO₂). Beyond their function as LEDs, these devices exhibit reversible resistive switching driven by field-assisted ion migration. Crucially, we demonstrate that this synaptic plasticity is optically tunable: illumination lowers the activation energy for ionic motion, reducing switching thresholds and modulating the hysteresis loop. This dual-mode response allows the material to function as an artificial synapse where weights are dynamically adjusted by visual input, mimicking biological neuromodulation and allowing optical control of synaptic plasticity.

Culminating in the sensory frontend, we optimized this perovskite system into a mixed-phase CsPbBr₃/Cs₄PbBr₆ nanocrystal architecture integrated with chemical vapor deposition (CVD) grown single-layer graphene (SLG). Through precise annealing control, we engineered a "raisin-bread" structure where photoactive CsPbBr₃ nanocrystals are embedded within a protective Cs₄PbBr₆ matrix. This synergistic design yields exceptional device performance:

By uniting the computational robustness of h-BN logic, the adaptive learning capabilities of optically controlled perovskite synapses, and the superior detectivity of graphene-enhanced quantum dots, this work establishes a scalable, material-efficient route toward monolithic intelligent optical biosensors capable of in-sensor computing.

Scaling up perovskite light-emitting diodes (PeLEDs) remains challenging because interfacial quenching, charge imbalance, and efficiency roll-off become increasingly pronounced as device dimensions increase. Building on our previous work published in Nanoscale, where we first demonstrated the benefits of polymer-assisted interfacial engineering in nanocrystal-based emitters, this study advances that concept toward fully scalable architectures. We establish a comprehensive process–structure–performance framework for large-area PeLEDs by employing a thin polyvinylpyrrolidone (PVP) interlayer whose microstructure is stabilized through controlled vacuum conditioning. This combined strategy reduces interfacial quenching, enhances layer densification, and effectively removes residual solvents, thereby spatially decoupling the emissive nanocrystal layer from the hole-transport interface.

Through a systematic exploration of several processing parameters and device architectures, we demonstrate that PVP-assisted recombination-zone displacement and vacuum-driven solvent removal act synergistically to enhance charge balance and maintain stable emission at high brightness. Correlative analysis between deposition conditions, interlayer morphology, exciton dynamics, and electroluminescent behavior reveals clear trends: optimized interfacial passivation strengthens radiative recombination, suppresses non-radiative pathways, and significantly mitigates efficiency roll-off under elevated current densities. Moreover, stabilizing the polymer microstructure results in more uniform charge injection and delays the onset of degradation typically associated with larger pixels.

Overall, this work identifies vacuum-conditioned polymeric interlayers as a robust, generalizable strategy for enhancing the operational stability of solution-processed PeLEDs. Together with our previous findings [1], it provides a reproducible and scalable route toward high-efficiency perovskite emitters suitable for lighting and display applications.

The convergence of highly efficient emitting nanomaterials with additive manufacturing offers a transformative approach to optoelectronic device fabrication. In this work, we report the integration of CsPbBr₃ perovskite quantum dots (QDs) -characterized by a photoluminescence quantum yield (PLQY) of 96.7%, high-purity green emission at 508 nm, and a narrow linewidth of 16.5 nm- into photocurable resins for Two-Photon Polymerization (2PP).

While conventional integration strategies often result in aggregation and significant efficiency loss, we demonstrate the fabrication of intrinsically luminescent, defect-free 3D microstructures. Our method relies on a strategic surface ligand exchange, replacing long-chain DDAB (didodecyldimethylammonium bromide) with short-chain SCN⁻ (thiocyanate) ligands. This surface engineering is critical to facilitate hierarchical self-assembly, promoting the formation of highly ordered, isolated cubic superlattices within the polymer matrix.

This structural organization preserves the optoelectronic integrity of the QDs in the printed nanocomposites. Spectroscopically, the transition to the superlattice state is evidenced by a distinct redshift of the emission peak to ~521 nm. Rather than attributing this shift to degradation, we identify it as a signature of electronic coupling between the ordered nanocrystals. Furthermore, Time-Resolved Photoluminescence (TRPL) analysis reveals a marked modification in emission dynamics, characterized by the emergence of an ultrafast decay component (≈ 0.75 ns). We interpret this acceleration as evidence of collective emission phenomena, arising from coherent emitter interactions within the superlattice.

These findings suggest that the resin acts not merely as a passive scaffold, but as an active medium that supports the organization of quantum emitters into functional superstructures. This work establishes a roadmap for high-resolution 3D printing of active photonic components, with potential applications in on-chip quantum light sources.

Ultrafast scintillation is a central requirement for next-generation time-of-flight positron emission tomography (ToF-PET), collider calorimetry, and high-rate particle tracking, yet virtually all commercial scintillators still funnel deposited energy into incoherent recombination of localized carriers. This structural bottleneck enforces a long-standing trade-off between light yield, timing, and spectral self-absorption in direct emitters, and prevents the use of quantum-coherent observables in radiation detection. Here we report a route beyond this limit by harnessing cooperative emission in quantum-ordered lead-halide perovskite nanocrystal (NC) superlattices (SLs), and by demonstrating, for the first time, superfluorescence (SF) directly triggered by ionizing radiation.

Our platform consists of highly monodisperse CsPbBr₃ NCs self-assembled into long-range ordered SLs, forming large continuous domains with orientational locking and electronic coherence across many dots. Structural characterization by transmission electron microscopy and electron diffraction confirms the cubic NC lattice and the mesoscale order required for cooperative light-matter coupling. We first establish the emergence of SF under optical excitation through ps-fast streak camera measurements, observing the delayed build-up of a narrow, red-shifted emission band whose intensity and lifetime follow the expected fluence- and temperature-dependent cooperative scaling. These signatures confirm that the SLs support macroscopic polarization and collective radiative decay over coherence volumes encompassing many NCs.

We then probe scintillation under X-ray excitation. Strikingly, the radioluminescence (RL) from the SLs is dominated (>90%) by a superfluorescent collective state, yielding bright picosecond photon bursts with effective scintillation lifetimes as short as ~40 ps at 20 K and persisting with minimal degradation up to and beyond the technological cornerstone of 80 K for nitrogen-based cryogenics. From second-order correlation (g²) kinetics we extract the ~40 ps timescale, placing SF scintillation among the fastest radiative responses reported under ionizing excitation. Crucially, SF emission is red-shifted by ~60 meV from uncoupled NC emission and by up to ~100 meV from the SL absorption edge, effectively suppressing reabsorption even in dense architectures.

To connect these cooperative optical signatures to ionization physics, we perform Geant4 Monte-Carlo simulations of energy deposition in a SL. The simulations indicate that secondary electrons generated by high-energy X-photons localize deposited energy within close-packed NC tracks on length scales consistent with coherence volumes, providing a realistic pathway for stochastic ionization cascades to seed coherent many-body emission.

Together, these results position solution-processable perovskite NC superlattices as coherent scintillating metamaterials in which collective radiative decay sets the ionizing-radiation response, offering a practical route to ultrafast, reabsorption-free nanoscintillators compatible with metascintillator architectures and potentially enabling detector concepts sensitive not only to light yield but also to the timing and statistical structure of the emitted photons.

Cesium lead bromide (CsPbBr3), a promising direct X-ray detector material, faces challenges due to the instability of its dark current, which is often attributed to the movement of mobile ions under an electric field. However, direct measurement of ions movement in perovskite has been seldom reported. Using grazing incidence X-ray fluorescence (operando GIXRF) on CsPbBr3 polycrystalline thick films (~200µm), we directly investigated the accumulation of ions under the electrode under bias [1]. A quasi monochromatic X-rays beam with energy of 17.5 keV (Mo Kα line) excites the material at low angle (0.5°) to probe the sample surface. X-ray fluorescence was monitored from a normal angle and the dark current is registered during the experiment. Our findings reveals that both Cs+ and Br- ion (or their vacancy counterpart) migrate, accumulating under or moving away the electrode according to the electric field direction, while Pb remains stable. Over a few hours, accumulation rates exhibit a linear relationship with the electric field, with coefficients of ~2 × 10⁻³ % h^-1V^-1mm for Br and Cs. The dark current and the ion accumulation correlate, and the current drift for positive bias is thousand times higher than that for negative bias because of asymmetrical Cr/CsPbBr3/ITO contact. Long term accumulation of species should lead to material modification. Phase modification was probed using Bragg-Brentano diffraction (operando XRD). Under long term polarization, evidence of decomposition of CsPbBr3 into CsBr, Cs4PbBr6 and CsPb2Br5 was observed, which also correlates with dark current drift. Overall, this study provides valuable insights into ion movement within CsPbBr3, potentially aiding development of more stable X-ray detectors.

Next-generation photonic technologies demand photodetectors that combine high responsivity, low noise, and scalable manufacturing routes. Metal-halide perovskites are rapidly emerging as a leading candidate due to their tunable optoelectronic properties and compatibility with low-temperature solution processing. Here, we present a comprehensive investigation of triple-cation perovskite photodetectors based on a p-i-n architecture employing Csₓ(FA₀.₁₇MA₀.₈₃)₁₀₀₋ₓPb(I₀.₈₃Br₀.₁₇)₃ absorbers. Devices fabricated via spin coating already demonstrate outstanding performance, including suppressed dark current, reduced hysteresis, broadband responsivity of ~0.3 A·W⁻¹, and fast temporal operation with rise times down to 38 μs. These characteristics yield a detectivity above 1×10¹² Jones, over five times higher than analogous n-i-p devices. The enhanced behavior is attributed to optimized interfacial energetics and efficient charge extraction mediated by 2PACz and C₆₀ transport layers, which minimize trap density and ensure stable diode-like operation. Structural and morphological analysis of the perovskite films reveals densely packed, pinhole-free polycrystalline layers with uniform thicknesses near 560 nm and grain sizes predominantly in the 300-400 nm range. The frequency-dependent response further highlights the superiority of the p-i-n design, preserving high normalized output up to kHz modulation and reaching the -3 dB cutoff at ~9-10 kHz. Building upon these results, this work outlines a pathway toward scalable fabrication via blade coating, a technique particularly attractive for large-area photonic integration. Although current data are based on spin-coated films, the morphological robustness of triple-cation compositions suggests strong compatibility with blade-coated deposition, enabling controlled thicknesses below the grain-size threshold and potentially improving carrier transport and noise suppression even further.

Overall, this study establishes the p-i-n perovskite photodiode as a high-performance, low-noise platform while charting a clear route toward scalable processing for next-generation photonic systems, from optical communication to precision sensing.

X-ray detectors play a vital role in medical diagnostics, industrial inspection, and security screening. However, widely used commercial direct-conversion detectors based on amorphous Si or Se typically offer sensitivities below 100 μC Gy⁻¹ cm⁻² and demand high fabrication costs, limiting performance in applications that require extremely low radiation doses. Hybrid organic–inorganic perovskite halides (HOIPs) have recently emerged as attractive alternatives due to their strong X-ray attenuation, large mobility–lifetime product, and compatibility with scalable solution processing. While single-crystal perovskites can deliver exceptional sensitivity, their growth and device fabrication remain complex. In contrast, spin-coated polycrystalline perovskites provide a rapid and low-cost route, yet film thickness—and thus sensitivity—is inherently restricted by conventional processing. [1]

Here, we overcome these limitations using a hot spin-coating strategy to deposit thick formamidinium lead halide (FAPbBr₂I) layers for lateral X-ray detectors based on interdigitated electrodes. The resulting films exhibit substantially improved attenuation and sensitivity. Importantly, we also evaluate the commonly overlooked contribution of air ionization surrounding the device, which can significantly inflate measured sensitivity and has seldom been rigorously addressed in prior studies. [2], [3] We find that this effect becomes especially pronounced in our ultra-small active-area devices (0.0002 cm²), where the ionized air volume is comparable to the device’s own active region. As a result, air ionization contributes 79% of the collected charge, inflating the apparent sensitivity by a factor of 4.8. However, our detectors still demonstrate an apparent sensitivity of 988.7 ± 16.9 μC Gy⁻¹ cm⁻² when the air contribution is included, whereas the corrected intrinsic sensitivity is 206.7 ± 5.5 μC Gy⁻¹ cm⁻². This real sensitivity surpasses most previously reported spin-coated perovskite devices and exceeds that of commercial amorphous semiconductor detectors, confirming the suitability of our approach for low-dose medical imaging and industrial non-destructive evaluation.

Furthermore, this work demonstrates the substantial measurement error introduced by atmospheric ionization, emphasizing that its removal is essential for accurate characterization of direct-conversion X-ray detectors. We apply a reference-device methodology to decouple true device response from air contributions,[4] providing a reliable framework for future studies of small-area spin-coated perovskite X-ray detectors.

CsPbBr₃ microcrystals washing strategy enabling low dark current and improved limit of detection for X-ray detection

Nil Monrós Oliveras,¹ Bapi Pradhan,¹ Elke Debroye¹

¹Department of chemistry, KU Leuven, Belgium

nil.monrosoliveras@kuleuven.be

All-inorganic CsPbBr₃ perovskite has emerged as a potential material for optoelectronic applications such as solar cells, LEDs, photodetectors, and X-ray detectors, owing to its superior charge-transport properties, long carrier diffusion length, and broad light absorption.^[1] In contrast to its organic counterparts such as MAPbBr₃ (MA = methylammonium), all-inorganic CsPbBr₃ exhibits superior photostability, thermal stability, and moisture stability, making it a suitable candidate for high-energy radiation detection.^[2]

Dimethyl sulfoxide (DMSO) is a widely used solvent for the synthesis of halide perovskites (HPs); nevertheless, its intrinsically high viscosity and boiling point can lead to degradation and reduced optoelectronic performance in the resulting perovskite films due to DMSO trapping during film formation, which generates voids.^[3] One of the major issues with CsPbBr₃ is the large dark current generated by the intrinsic ionic-migration nature of the material, film quality and device architecture.^[2] Such large dark currents can compromise device stability and degrade X-ray image quality.

In this presentation, I will discuss the synthesis of CsPbBr₃ microcrystals (~20/50 μm) for X-ray detection. I will elaborate on the impact of washing these DMSO-synthesized microcrystals with different solvents (such as ethanol (EtOH) and ethyl acetate (EA)) and examine how these solvents affect the structural, optical, and X-ray detection properties of CsPbBr₃ microcrystals. To evaluate their practical applicability, proof-of-concept X-ray detectors based on wafers composed of these microcrystals have been developed.

Compared with their non-washed counterparts, CsPbBr₃ microcrystals washed with a combination of EA and EtOH exhibit a reduced dark current and suppressed dark-current drift. These results hint on reduced void generation leading to an improved on/off ratio and an X-ray limit of detection (LoD) decreased by more than one order of magnitude. This performance is very promising for the generation of future X-ray detector devices with a long-term robust response.

Perovskite-based photodetectors have gained significant attention due to their high absorption coefficients, tunable bandgaps, and excellent optoelectronic properties. In this study, SCAPS-1D numerical modelling was employed to design and optimize a vertical photodetector architecture using CsPbI₃ as the active absorber layer. A systematic optimization strategy was implemented by varying the material selection and physical parameters of the electron transport layer (ETL), hole transport layer (HTL), and perovskite layer. Among the evaluated candidates, WS₂ and Cu₂O emerged as the most suitable ETL and HTL materials, respectively, owing to their favourable band alignment and efficient charge transport characteristics. Critical device parameters—including layer thickness, doping density, defect concentration, interfacial trap states, and electrode work functions—were extensively analysed. The optimized structure, FTO/WS₂/CsPbI₃/Cu₂O/Au, achieved a short-circuit current density of 20.126 mA/cm², a responsivity of 0.48 A/W, and a specific detectivity of 9.5 × 10¹⁰ Jones under a −0.5 V bias. The device exhibited peak photoresponse within the 650–700 nm spectral region and delivered an overall power conversion efficiency of 16.64%. These results demonstrate the value of simulation-driven design in identifying performance-enhancing material combinations and device configurations. Overall, the findings highlight the strong potential of CsPbI₃-based vertical photodetectors for visible-light sensing and provide a solid framework for their future experimental realization.

Photodetectors (PDs) are essential components in modern optoelectronics, converting light into electrical signals for applications such as imaging, environmental monitoring, optical communications, and wearable sensors. Their performance is evaluated by metrics like responsivity, detectivity, response speed, and stability. Achieving high performance while maintaining scalability, flexibility, and cost-efficiency remains a major challenge for next-generation devices [1].

Halide perovskites have emerged as highly promising photoactive materials. They offer tunable bandgaps, strong optical absorption, long carrier diffusion lengths, low trap densities, and good thermal and ambient stability [2]. These properties enable efficient light harvesting and broad spectral detection. Furthermore, perovskites can be engineered into “raisin bread” architectures, where high-quality perovskite grains are embedded in a secondary phase. This two-phase system not only improves charge transport and broadens the spectral response but also enhances the structural and environmental stability of the perovskite layer, making devices more robust under operational conditions. However, their relatively low charge carrier mobility in thin films, limited by grain boundaries and defects, restricts photoconductive gain and overall device responsivity.

Graphene, a two-dimensional carbon material with exceptional carrier mobility (~40,000 cm²·V⁻¹·s⁻¹),can address this limitation [4]. Although its intrinsic light absorption is low (~2.6%), its ultrafast charge transport makes it an ideal partner for perovskite-based photodetectors. By forming graphene-perovskite hybrids, one can achieve efficient charge extraction, and significantly enhance gain and responsivity.

These hybrid devices exhibit remarkable performance, including broadband photodetection, high responsivity exceeding 57,000 A/W excellent repeatability over multiple on/off cycles, and long-term operational stability in ambient conditions for over six months. Moreover, maskless, vacuum-free inkjet printing allows direct deposition of perovskites onto graphene, supporting flexible substrates and scalable fabrication [5,6].

Graphene-perovskite hybrid photodetectors thus combine the best of both materials, offering a versatile, high-performance platform for next-generation optoelectronic systems. Their potential spans wearable devices, artificial vision, environmental sensing, and other applications requiring sensitive, fast, and reliable light detection.

Photonic structures sustain optical resonances that amplify light–matter interactions, enabling more efficient light management and, consequently, improved performance in optoelectronic devices. Nevertheless, emerging optoelectronic technologies rely on cost-effective and large-scale manufacturing techniques that can reduce expenses and boost production efficiency. To harness the remarkable attributes of nanophotonic structures for enhancing these devices, they must also be produced with high throughput processes.

In our research group, we employ soft nanoimprinting lithography, a versatile, rapid, and cost-efficient method for creating nanostructures from a diverse variety of materials. In soft nanoimprinting lithography, we make use of pre-patterned soft elastomeric stamps to fabricate photonic structures out of materials such as resists, biopolymers, colloids and nanomaterials in general. In all cases, the resulting photonic architectures can exhibit a resolution below 100 nm while covering large areas (typically 1 cm²).

During this presentation, I will demonstrate our utilization of pre-patterned stamps to induce the long-range alignment of different metal colloids and perovskite nanocrystals, to attain distinct optical properties, such as lattice resonances with high Q-factors. I will also show how nanoimprinting lithography can be used to produce chiral photonic architectures in an efficient and simple way. These chiral nanostructures support strong chiral resonances that are used to impart chirality to the emission of otherwise non chiral materials such as perovskite nanocrystals, quantum dots or dyes placed near the architecture and resulting in large values of circularly polarized photoluminescence reaching figures of merit (glum) beyond 1. [1,2]

In hybrid metal halide perovskites, chiroptical properties can arise from structural symmetry breaking by incorporating a chiral A-site organic cation within the structure. Similarly, we can induce highly efficient remote chirality transfer where chirality is imposed on an otherwise achiral hybrid metal halide semiconductor by a proximal chiral molecule that is not interspersed as part of the structure yet leads to large circular dichroism dissymmetry factors (gCD) of up to 10⁻². These two forms of chirality induction will be presented in 2D and quasi 2D/3D compositions. We systematically investigate the layer number (n-value) dependence and emergent trade-offs in chiroptical properties, spin-relaxation times, and carrier mobilities. Furthermore, we show a variety of devices with functionality that benefits from the chirality using the chiral induced spin selectivity effect. These findings establish a structure-property relationship between CISS and structural chirality, providing new design principles for controlling charge-to-spin interconversion and advancing chiral opto-spintronic semiconductors.

Halide perovskites are revolutionizing the field of optoelectronic devices, encompassing applications from solar cells to LEDs, thanks to their outstanding optical and electrical properties. These materials are characterized by high absorption coefficients, long carrier diffusion lengths, and efficient charge transport, positioning them as frontrunners in advanced technology development. Perovskite solar cells (PSCs) have now exceeded 27% efficiency, making them the leaders among thin-film technologies. However, despite their high efficiency, the widespread commercialization of three-dimensional (3D) perovskites is hindered by their instability, particularly in humid environments, as their soft ionic lattice degrades upon exposure to moisture and oxygen, presenting a significant challenge to their long-term viability. To address this, quasi-two-dimensional (2D) perovskites have emerged as promising alternatives. Their layered structure, incorporating larger organic cations, enhances environmental stability by shielding the inorganic framework from degradation. In addition, in these materials the electronic properties, such as bandgaps and exciton binding energies, can be precisely adjusted, essential for optimizing device performance.

The charge dynamics and transfer processes in thin films of mixed-dimensional quasi-2D MAPI-based perovskites will be presented. By combining femtosecond transient absorption spectroscopy (FTAS) and photoluminescence (PL), the role of specific n-phases in the charge transfer dynamics will be discussed in the light of the correlation between the phase distribution within the film and the corresponding band-alignment.[3,4] Particular attention is given to the temporal evolution of photobleaching features, which reveals charge transfer and separation between higher- and lower-dimensional phases.

Our findings emphasize the critical importance of controlling the dimensionality gradient in active materials composed of mixed 2D perovskites, optimizing charge transport and separation by promoting efficient transitions between low-n and high-n phases.

The continuous development in smart devices and microsystems for the control of industrial processes, biomedical sensors and instruments, visible and NIR light communications, photovoltaics and many other applications, is triggering new demands for novel and low cost semiconductors. Metal halide perovskites can be a good solution, because of their good optoelectronic properties and tolerance against crystalline defects, other than low-cost processing and low CO₂ footprint. Particularly, 2D lead halide perovskites, such as PEA₂PbI₄ and higher order Ruddlesden-Popper phases, can be easily synthesized in the form of single cyrstals with a multilayered structure defined by the octahedral planes of PbI₄^- separated by the long organic cations PEA⁺ and stacked by van der Waals interaction. In this way, multilayered nanoflakes can be exfoliated from single crystals in a wide range of thicknesses (tens to hundreds of nm) and lateral sizes of several tenths of microns in order to study their optical and optoelectronic properties. These nanoflakes were transferred onto micrometric photodevices by using Pt-prepatterned Si/SiO₂ substrates with 10 µm of channel length. In such devices, photocurrents from 10 pA to 100 nA can be measured at relatively low voltage bias (around 1 V) under 450 nm laser light with incident powers in the range from 10 pW to more than 500 nW in steady state. The linear behaviour of photocurrent with incident power and a near constant responsivity would be indicative of a negligible presence of nonradiative channels associated to deep levels, whereas a sublinear response of the photocurrent to power can be characteristic of trap sensitized photoconductivity in the semiconductor. The spectral photoresponse exhibits a clear exciton resonance, slightly red-shifted with respect to micro-photoluminescence (µPL) due to reabsorption. Furthermore, the rise/decay of the photocurrent is very fast, < 1 µs, hence with a cut-off frequency over the MHz. Interestingly, µPL images showed that the lower energy component present in the PL spectra is being emitted by the edges of the perovskite nanoflakes. Our results on samples with different thicknesses point out to phototransport taking place at the monolayer/s touching the Pt-contact with photogenerated carriers originated from direct absorption followed by those produced from photons re-emitted at top monolayers and absorbed at the bottom ones.

Trap states in Sn-based perovskite reduce the carrier lifetime and responsivity of related photodetection devices. To address this challenge, thiophene-2-ethylammonium halides (TEAX, where X = I, Br, or Cl) were introduced, with the potential to enhance FASnI3 perovskite crystallization[1]. Herein, quasi-2D/3D FASnI₃ photodiodes (PDs) fabricated using TEAX, and their photodetection parameters were systematically characterized in correlation with photovoltaic parameters. The addition of TEAI to the active layer of the self-powered PD results in a maximum responsivity of 0.45 AW−1 at 680nm and 0.20 A·W⁻¹ at 840 nm, maintaining sensitivity up to 900 nm. Furthermore, the devices exhibited ultrafast rise and decay times of 1.45 µs and 1.95 µs, respectively, which are among the best reported values for Sn-based perovskite photodiodes[2,3]. By optimizing the C₆₀ thickness in the PIN configuration, dark current and the minimum detectable optical power are reduced. Finally, trivalent cations Sb³⁺ and In³⁺ were added to neutralize the Sn²⁺ vacancies in the best-performing samples, and further improvement of the photocurrent was achieved by the addition of InCl₃. These results highlight TEAX-treated quasi-2D/3D FASnI₃ photodiodes as promising candidates for high-performance, and broadband lead-free perovskite photodetectors. However, fabricated devices still suffer from limited V_OC, which we are confident to increase in the near future by using more appropriate charge-transport layers.

The triple-cation lead halide perovskite (Cs_xMA_yFA_1-x-yPb(I_zBr_1-z)₃) and tin halide perovskite (FASnI₃) demonstrate promising optoelectronic characteristics, such as enhanced light absorption, adjustable bandgap, and efficient carrier transport. Furthermore, their cost-effective solution-based synthesis methods render them highly attractive for photodetection applications. To the best of our knowledge, most existing reports focus on photodiodes (PDs) based on a single perovskite material system, either lead or tin, whereas direct comparative studies evaluating both materials under identical device architecture and measurement conditions are scarce. Therefore, we are motivated to present a systematic side-by-side comparison of triple-cation lead and FASnI₃-based p-i-n (inverted) PDs, benchmarking key figures of merit including dark current, responsivity, noise, detectivity, dynamic range, and frequency bandwidth. Both types of devices were encapsulated with epoxy and measured in ambient conditions over several weeks and even months. According to this study, the triple-cation perovskite-based photodiode (Tri-Cat PD) exhibited superior performance compared to the FASnI₃-based photodiode (FASI-PD). For instance, dark currents at zero bias are in the order of 10^-10 A and 10^-9 A for Tri-Cat PD and FASI-PD, respectively. Furthermore, Tri-Cat PDs exhibit the highest responsivity and detectivity, reaching maximum values of 0.46 A/W and 7 x 10¹³ Jones, respectively, at λ = 735 nm. FASI-PD exhibits a maximum responsivity and detectivity of 0.34 A/W and 10¹² Jones, respectively, at λ = 685 nm, with a wavelength detection limit extending up to 900 nm. Notably, Tri-Cat PDs exhibit a fast response with a cut-off frequency of 9 kHz, in contrast to the 5 kHz for FASI-PDs. These findings unequivocally demonstrate the superiority of Tri-Cat PDs over FASI PDs, utilizing the same architecture and charge transport layers. Despite these results, our findings on lead-free PDs are encouraging, prompting further improvements, specifically by reducing the tin oxidation and tin vacancies during the preparation process, as well as employing more suitable charge transport layers.

Mixed-valence gold halide perovskites such as Cs₂AuᴵAuᴵᴵᴵX₆ (X = Cl, Br, I) have recently emerged as a compelling platform for next-generation photonic technologies, offering intrinsically lead-free compositions, strong electron–phonon interactions, and ultralow bandgaps. Landmark advances—from the stabilization of Au²⁺ in 3D halide frameworks [1] to the identification of an indirect polar valley limiting radiative efficiency [2]—have highlighted the unique mixed-valence physics of these systems.

In this talk, I will present our latest results on the synthesis, structural control, and optoelectronic properties of the Cs₂AuᴵAuᴵᴵᴵX₆ family. Building on recent low-temperature synthesis strategies [3], we combine single-crystal growth, thin-film deposition, and advanced optical spectroscopies to unravel the mechanisms governing both light absorption and emission in these ultralow-bandgap double perovskites.

Cryogenic and temperature-dependent measurements reveal a remarkably red-shifted self-trapped exciton (STE) luminescence, displaced by approximately 400 meV from the absorption edge. This STE emission arises from the strong lattice distortions and mixed-valence Auᴵ/Auᴵᴵᴵ configuration characteristic of Cs₂AuᴵAuᴵᴵᴵX₆. In parallel, we identify a pronounced ~100 meV Urbach tail—consistent with the indirect polar valley physics previously reported [2]—which provides an efficient nonradiative relaxation channel and plays a key role in quenching the radiative emission through dense phonon-assisted intragap states.

Together, these findings provide a unified picture of strong exciton–phonon coupling, disorder-induced band tailing, and polaron formation in gold-based halide perovskites, and define the fundamental limits and opportunities for deploying Cs₂AuᴵAuᴵᴵᴵX₆ materials in next-generation infrared detectors and light-emission devices.

                  Perovskite solar cells are emerging as a low-cost and highly favorable alternative to conventional silicon-based photovoltaics. Now reaching a record-high power conversion efficiency of 26.95 %. However, two major challenges currently hinder their commercialization: long-term stability under illumination and the risk of environmental contamination by lead; a third challenge lies ahead – recyclability. This talk addresses these issues head-on, exploring strategies to overcome them and enable the sustainable deployment of perovskite PV technologies.

                  Stability – The stability of perovskite solar cells (PSCs) is governed by both intrinsic and extrinsic factors. Intrinsically, stability is largely determined by the interfaces between the perovskite and the charge-transport layers and electrodes, while the perovskite absorber itself remains stable under dry and reducing atmospheres. Extrinsically, long-term stability requires effective encapsulation to prevent degradation induced by moisture, oxygen, and thermal cycling. This talk will present a low-temperature, hermetic laser-based glass-sealing process that encapsulates the active layers under a dry, inert atmosphere, providing robust protection from external instability factors. Experimental data from highly durable devices will be shown, demonstrating extrapolated operational lifetimes exceeding 2500 h under AM 1.5G continuous illumination.

                  Lead sequestration – The most efficient perovskite solar cells rely on lead-based absorbers. These lead-containing compounds are water-soluble and, therefore, can cause harm to the environment in the event of a leak. This talk will present a strategy based on highly reactive scavenging species that, upon exposure to humidity, trigger the rapid conversion of perovskite-derived lead into water-insoluble compounds. A novel, low-cost inorganic lead-capturing layer with a sequestration efficiency exceeding 99 % will be introduced. Combined with glass encapsulation, this approach aims to ensure compliance with stringent environmental regulations related to lead.

                  Circularity – In perovskite solar modules, the transparent conducting oxide (TCO)/glass substrates represent the most valuable components. To enable circularity and reduce lifecycle costs, it should be possible to dismantle the module at end-of-life, remove the aged active layers, and re-apply fresh ones. This can be achieved through a recently developed de-sealing process that allows the glass-encapsulated device to be opened, providing direct access to the functional layers. After refurbishment, the module can be re-sealed using the laser-assisted glass encapsulation process, which enables a renewed operational lifetime and promotes the true closed-loop use of materials.

Achieving both high efficiency and long-term stability in perovskite solar cells (PSCs) remains a major challenge and an active area of research. At LPEM-CNRS, our team focuses on uncovering the fundamental degradation mechanisms in PSCs and developing engineering strategies to mitigate them. In this presentation, I will highlight recent work from our group¹ that leverages nanoscale structural-property investigations to elucidate the physical and chemical processes governing the degradation and passivation of functional PSCs.

While extensive efforts have been made to understand degradation mechanisms, direct probing of the buried interfaces, where critical degradation often initiates, has remained elusive. In this work, we introduce a new in situ methodology that harnesses the nanothermometric properties of embedded upconversion fluoresent nanoparticles (UCNPs) placed at the buried perovskite/hole transport layer (HTL) interface. This approach allows, for the first time, real-time tracking of local interfacial temperature evolution during light-induced accelerated degradation, while simultaneously monitoring the device's optical and photovoltaic performance. Applied to PSCs with different perovskite compositions, this technique reveals non-trivial thermal signatures and distinct degradation regimes correlated with structural and optical changes observed via ex situ characterizations. The results uncover a dynamic interplay between heat accumulation, phase transformation, and material decomposition, offering insights into the spatiotemporal evolution of PSC degradation.

In parallel, we investigate passivation strategies aimed at improving PSC stability against humidity. Fluorinated molecules have shown promise in the literature as partial moisture barriers; however, previously reported short-chain variants offer only limited enhancement of the perovskite surface’s water-contact angle. Here, we explore a family of fluorosilane molecules capable of rendering perovskite surfaces superhydrophobic. Using a combination of spectroscopic techniques, I will discuss the interaction mechanisms between these fluorosilanes and the perovskite absorber, and their implications for device stability.

In recent years, high optical quality (i.e., negligible diffuse scattering) nanostructured perovskite films displaying intense excitonic bands have been integrated into Fabry-Pérot resonators, giving rise to strong light-matter coupling.[1-3] Under this regime, the electronic and photonic structure of the perovskite-cavity system undergoes a reconfiguration that gives rise to new hybrid light-matter states known as exciton-polaritons, which determine the absorption and emission properties of the ensemble. These advances have yielded significant milestones, like the observation of Bose-Einstein condensation in both two-dimensional (2D) perovskites[4] and quantum dot solids,[5] the latter at room temperature, as well as the possibility to study complex physical phenomena.[6]

In this talk, we will describe an alternative approach to achieve strong light-matter coupling in two-dimensional (2D) Ruddlesden-Popper perovskites integrated in optical cavities.[S. Gallego et al., In preparation] We will show that mesoporous scaffolds presenting a narrow nanopore size distribution provide unique opportunities both to (i) control the quality and phase-purity of the 2D perovskite synthesized within them, featuring single phase large transition dipole moments, and (ii) achieve intense and spectrally tunable cavity resonances, hence favoring the precise design of exciton-polaritons. Fine control of the cavity size, achieved by means of the precise control of the scaffold thickness, permits to accurately determine the absorption and emission properties of the ensemble, which displays the characteristic anticrossing behavior of the upper and lower polaritonic branches, a significant Rabi splitting above 200 meV and tunable photoluminescence properties fully controlled by the lower polariton.