Beatriz Romero

Perovskite solar cells rely on complex multilayer architectures whose mechanical integrity is increasingly recognized as a critical factor for long-term operational stability. Despite extensive characterization of methylammonium lead iodide (MAPbI₃), the mechanical properties of emerging multi cation perovskites within complete device stacks remain poorly understood. In this manuscript, we present a system level mechanical characterization of two perovskite solar cell architectures using depth resolved nanoindentation. By combining continuous stiffness measurements with statistical deconvolution, we isolate the elastic modulus and hardness of individual layers across the full device stack. The approach accurately reproduces reported values for common transport layers and MAPbI₃, demonstrating robustness. We further report, for the first time, the intrinsic mechanical properties of the four cation perovskite CsRbMAFAPb(IBr)₃, which exhibits a similar elastic modulus but substantially higher hardness than MAPbI₃. These results reveal enhanced resistance to mechanical damage in multi cation absorbers and underscore the importance of mechanical design considerations for improving the durability of next generation perovskite solar cells.

Halide perovskites (HPs) are promising materials for memristor devices because of their unique characteristics. In this study, nonvolatile resistive switching memory devices based on thick MAPbI₃ perovskite (800 nm) films with structure FTO/MAPbI₃/polymethyl methacrylate (PMMA)/Ag are presented. Reproducible and reliable bipolar switching characteristics are demonstrated with an ultra‐low operating voltage (−0.1 V), high ON/OFF ratio (10⁶), endurance (>2 × 10³ times) and a record retention time (>10⁵ s). The I–V curve of the first cycle exhibits self‐formed conductive filaments. These are attributed to the presence of metallic Pb resulting from an excess of PbI₂ in the perovskite film. The subsequent activation process involves the formation of conductive filaments, consisting of either iodide vacancies or migrated charged metals. Numerical simulations are then carried out to understand the nature of these conductive filaments and the role of the internal electric field in the migration of iodide ions, iodide vacancies, and Ag cations. Finally, an exhaustive model is proposed that explains the set and reset processes governing the first voltage cycle and the steady state, at different voltage ranges. In summary, this work offers a novel and thorough perspective of the complete resistive switching (RS) behavior in a MAPbI₃/buffer/Ag memristor, supported by numerical simulations.

Bias voltage scan rate and mobile ion concentration have a strong influence in J-V curves of metal halide perovskite-based memristors. In addition to hysteresis, in some cases J-V curves also show an anomalous drop in current known as negative differential resistance. This feature is usually related to electrochemical reactions between the reactive metal and I ^- ions, and to air exposure. However, in devices with low-reactive electrodes, its origin is still under debate. In this work, we propose a theoretical model based on ionic-electronic drift-diffusion. This model sheds light into the ionic-electronic processes that shape hysteresis, and it helps to explain the appearance and evolution of a negative resistance in memristors with low-reactive contacts and capacitive hysteresis. Finally, experimental J-V curves are presented to validate the proposed model.

Ideality factor vs. temperature obtained from the dependence of open circuit voltage on the irradiation level (inset).

Perovskite solar cells (PSCs) have become very popular due to the high efficiencies achieved. Nevertheless, one of the main challenges for their commercialization is to solve their instability issues. A thorough understanding of the processes taking place in the device is key for the development of this technology. Herein, J-V measurements have been performed to characterize PSCs with different active layer thicknesses. The solar cells’ parameters in pristine devices show no significant dependence on the active layer thickness. However, the evolution of the solar cells’ efficiency under ISOS-L1 protocol reveals a dramatic burn-in degradation, more pronounced for thicker devices. Samples were also characterized using impedance spectroscopy (IS) at different degradation stages, and data were fitted to a three RC/RCPE circuit. The low frequency capacitance in the thickest samples suffers a strong increase with time, which suggests a significant growth in the mobile ion population. This increase in the ion density partially screens the electric field, which yields a reduction in the extracted current and, consequently, the efficiency. This paper has been validated with two-dimensional numerical simulations that corroborate (i) the decrease in the internal electric field in dark conditions in 650 nm devices, and (ii) the consequent reduction in the carrier drift and, therefore, of the effective current extraction and efficiency.

Visible light communication systems can be used in a wide variety of applications, from driving to home automation. The use of wearables can increase the potential applications in indoor systems to send and receive specific and customized information. We have designed and developed a fully organic and flexible Visible Light Communication system using a flexible OLED, a flexible P3HT:PCBM-based organic photodiode (OPD) and flexible PCBs for the emitter and receiver conditioning circuits. We have fabricated and characterized the I-V curve, modulation response and impedance of the flexible OPD. As emitter we have used a commercial flexible organic luminaire with dimensions 99 × 99 × 0.88 mm, and we have characterized its modulation response. All the devices show frequency responses that allow operation over 40 kHz, thus enabling the transmission of high quality audio. Finally, we integrated the emitter and receiver components and its electronic drivers, to build an all-organic flexible VLC system capable of transmitting an audio file in real-time, as a proof of concept of the indoor capabilities of such a system.

We explain how to obtain closed-form analytic solutions from the set of equations that describe the three-diode lumped-parameter equivalent circuit model proposed by Mazhari [1] to portray the undesirable S-shape often observed in I-V characteristics of illuminated organic solar cells (OSCs), and occasionally seen in other types of solar cells. This allows quick extraction of the model's parameter values by directly fitting the resulting closed-form solution to the cell's measured I-V data. Such mathematical simplification of the extraction procedure facilitates individually studying the effect of each parameter on the illuminated OSC I-V characteristics, and thus on its power generation capacity. We illustrate application of the direct extraction procedure to measured I-V characteristics of an experimental OSC, which exhibits the illumination intensity-dependent S-shapes. The usefulness of the analytic solution to assess the effect of the model parameters is further corroborated by graphically illustrating the progression of a series of hypothetical synthetic I-V characteristics generated by this analytic solution using gradually changing the parameter values. Analysis of the results, in this case, indicates that activation of the diode that represents recombination is the key factor responsible for the emergence of the illuminated I-V curve's S-shape.