A defining feature of electron transport, ETp, through protein films is its remarkably weak temperature dependence, even over distances (15–35 nm) that far exceed the range predicted for coherent tunneling. We measure ETp across multilayer films of human serum albumin (HSA) and bacteriorhodopsin (bR) using Au/protein/Pd micropore (MpD) junctions with negligible contact resistance. Both proteins show stable current–voltage characteristics that are essentially temperature-independent from 0.2 to 300 K at applied biases from ±0.05 to ±1 V. These results exclude thermally activated hopping. The ~2 eV HOMO–LUMO gap and the absence of detectable electronic states near the electrode Fermi level rule out resonant transport. Time-dependent, voltagepulse, and impedance measurements exclude ionic conduction or interfacial artifacts. Together, these findings show that the experimentally observed ETp type is intrinsic to the proteins. The consistency of these findings across two structurally and functionally distinct proteins suggests that long-range temperature-independent ETp is a general property of dry protein films, arising from their collective electrical architecture, including peptide backbones, hydrogen-bond networks, structurally bound water (retained in the dry films), and electronic polarization. Together, these create a responsive three-dimensional environment capable of supporting long-range electron transport beyond the scope of conventional molecular electronics models.

By actually addressing the title question, we provide a comprehensive and critical review of self-healing (SH) in lead-based halide perovskites (HaPs), a phenomenon with profound implications for the stability of these materials across all applications, from photovoltaics to light emission and radiation detection. We emphasize reasoning as a guide to interpreting the dynamic balance between degradation and recovery when HaPs are exposed to light, heat, mechanical stress, or radiation. We compile and assess what are, in our view, the most relevant, available reports of damage-healing dynamics, distinguishing verified facts and observations from interpretations and unresolved questions. Key topics include damage accumulation, light soaking, and photo-brightening, as well as the mechanistic roles of lattice dynamics, halide migration, redox chemistry, and acid-base equilibria in the disappearance of defects on accessible time scales. Thus, we go beyond a conventional summary by providing a unifying framework to clarify contradictions in the literature and reveal the underlying principles of reversible damage. By consolidating results that are often scattered into a coherent picture, we strive to establish a foundation for predictive models of SH kinetics, while guiding strategies to stabilize devices. We anticipate that this critical synthesis will serve as an authoritative reference for the metal halide perovskite research field.

Quasi-2D halide perovskites are chemically synthesized realizations of quantum well stacks with giant exciton oscillator strengths, tunable emission spectra, and very large exciton binding energies. While these features render quasi-2D halide perovskites a promising platform for room-temperature polaritonics, bosonic condensation and polariton lasing in quasi-2D perovskites have so far remained elusive at ambient conditions. Here, we demonstrate room-temperature cavity exciton-polariton condensation in mechanically exfoliated crystals of the quasi-2D Ruddlesden-Popper iodide perovskite (BA)2(MA)2Pb3I10 in an open optical microcavity. We observe a polariton condensation threshold of 0.41 µJ cm−2 per pulse and detect a strong non-linear response. Interferometric measurements confirm the spontaneous emergence of spatial coherence across the condensate with an associated first-order autocorrelation reaching 0.6 with 1 ps coherence time and an effective de Broglie wavelength of 13 µm. Our results lay the foundation for a new class of room-temperature polariton lasers based on quasi-2D halide perovskites with great potential for hetero-integration with other van-der-Waals materials and combination with photonic crystals or waveguides. The authors report the experimental observation of room-temperature condensation of exciton polaritons in quasi-2D layered crystals of halide perovskite, integrated into an open optical microcavity. These materials combine van-der-Waals properties with dominant exciton physics at room temperature.

Sustainability of energy conversion materials depends on their functional resilience. Such can be achieved by self-healing, SH, which requires mass transfer inside the material. Unfortunately, we lack guidelines as to which physical and chemical material properties can help predict if a material can self-heal and how. We report a data-driven approach to find such properties, using experimental and computational data from materials databases. We focus on four properties: optical deformation potential (ODP), relative structural polarization (RSP), ionicity, and hardness to distinguish SH materials from others. ODP with RSP predict the two main SH mechanisms in semiconductors: mass transfer of kinetically stabilized (class I) or thermodynamically stabilized (class II) defects. In crystals with covalent bonding, the correlation of hardness with ionicity & RSP emphasizes effects of the nature of the chemical bonding on the SH mechanism. Our approach and results present significant steps to find SH materials for various applications, especially for energy conversion.

The design, fabrication, and application of robust metal/protein/metal junctions are presented with ultrathin (≈20 nm) protein films demonstrating long-term stability in ambient conditions and preserving their electron transport behavior also at ≈10 K. These junctions establish a reliable platform with a permanent contact configuration, where the confined protein layer retains its functional activity after metal contact evaporation on the protein. A bottom-up micropore device (MpD) fabrication strategy is used and optimized to ensure reproducibility. The sub-nanometer roughness of the bottom electrode is preserved within the micropore, enabling uniform protein layer deposition and film formation. In the MpD structures, protein layers are integrated between Au-covered substrates and an e-beam evaporated Pd contacts. Depositing multi-layered protein films allows for defining film widths, as tested by the atomic force microscopy (AFM)-based scratching technique. The films are composed of human serum albumin (HSA) and bacteriorhodopsin (bR). Pd's preferred 2D growth minimized metal penetration and short circuits. Impedance phase response analysis shows that ≈60% of the junctions are functional ones, demonstrating the effectiveness of the fabrication approach. These protein-based MpD junctions provide a basis for future stable platforms for electron transport studies of bio- and other soft materials.

Lead halide perovskites (HaPs) have gained much attention, especially for use in photovoltaics and optoelectronic devices. However, stability remains the major roadblock to implementing HaP-based devices. Self-healing, the material's intrinsic tendency to recover from damage without any external aid, is observed in HaPs. Yet, understanding of its detailed mechanism is still lacking. Fluorescence recovery after photobleaching and photoluminescence (PL) imaging are used to monitor changes in HaP polycrystalline thin films in both space and time following damage, through the self-recovery path. Changes in PL outside the excitation spot are identified immediately following photodamage for both CsPbI3 (CsPI), showing photo-darkening, and MAPbI3 (MAPI), exhibiting photo-brightening. During self-healing of the directly illuminated spot, MAPI peripheral fluorescence decreases to its initial level, whereas CsPI exhibits photo-brightening to above the original level. This can be correlated with processes occurring on two time scales: rapid electronic defect passivation and slower ion migration. Investigating PL dynamics under intense laser damage demonstrates that changes to PL can be attributed to a combination of charge carrier trapping and trap removal in the early stages and ion migration and redox reactions in later stages. The understanding of spatio-temporal dynamics of damage and self-healing can promote longevity of HaP-based devices.

Photovoltaic (PV) technology is crucial for the transition to a carbon-neutral and sustainable society. In this Review, we provide a comprehensive overview of PV materials and technologies, including mechanisms that limit PV solar-cell and module efficiencies. First, we introduce the PV effect and efficiency losses within the framework of the Shockley–Queisser model for solar-to-electrical power conversion. However, all PV technologies fall short of these idealizations in various aspects, from incomplete sunlight absorption to the loss of photocurrent and photovoltage caused by the recombination of photogenerated charge carriers in the cells. Approaching the efficiency limits of PV technology requires material innovations and device designs that minimize these losses. Solar-cell research and development presents several solutions to these problems that are intimately related to the properties of the specific PV materials. To increase efficiencies beyond the Shockley–Queisser limit (around 33

In recent years, the photovoltaic community has shown a growing interest in lead-free halides perovskites (HaPs), i.e., ABX3 where B not equal Pb, A = monovalent cation and X = halide, as candidates to solve some of the issues inherent to their lead-based cousins. The gold HaP family (A2Au2X6, with mono- and tri-valent Au) is one such example and has been getting increasing attention from theoretical and experimental points of view. In particular, because of the mixed valence character of the gold species, the compounds are double perovskites, A2AuIAuIIIX6. We report a simple synthesis route to obtain inorganic gold HaP (Cs2AuIAuIIIX6, with X = I, Br, Cl) powders at low temperatures, and present thermodynamic constants associated with these materials. We confirm the structure of the compounds by XRD and Raman spectroscopy in accordance with the mixed valence character of the Au species. Additional chemical analyses using XPS and SEM/EDX confirm the stoichiometry of the compounds, though surface iodine deficiency was observed for Cs2AuIAuIIIX6. These results further elucidate the potential of these materials for optoelectronic applications. We report the photoluminescence (PL) spectra for this family of materials to demonstrate their potential photo-activity, with bandgaps in the range of 1.4 eV to 1 eV. Hence, our results open the door to dedicated studies of gold halide perovskites towards possible future integration of these materials in optoelectronics, such as photovoltaic (PV) applications.

The solid-state protein junctions have shown efficient electron transport over a few tens of nanometer lengthscale. This work demonstrates, how the contact resistance ( R C ̂ $\widehat {{R_{\mathrm{C}}}}$ ) of a solid-state protein junctions, treated as a contact-limited process, which can be extracted quantitatively from the measured junction resistance (RP) by using the extrapolated zero-length resistance and series resistance (RS). Alternating current (impedance spectroscopy) and direct current measurements are used to examine charge transport in junctions of human serum albumin (HSA) and bacteriorhodopsin (bR) films with varying thicknesses. Three contact configurations, Si-Au, Au-eutectic gallium indium (EGaIn), and, in a micropore device (MpD), Au-Pd, are compared. While Si-Au and Au-EGaIn junctions exhibit substantial R C ̂ $\widehat {{R_{\mathrm{C}}}}$ that are ascribed to interfacial oxides and electrostatic protein-electrode interactions, MpD effectively eliminates R C ̂ $\widehat {{R_{\mathrm{C}}}}$ , enabling measuring the intrinsic electron transport across HSA and bR films. The exponential length-dependence of RP shows a transport decay constant (β) that varies with interfacial conditions, underscoring the role of contact engineering. By minimizing R C ̂ $\widehat {{R_{\mathrm{C}}}}$ , exceptionally low β values (≈0.7-1.1 nm-1) are found, proving that, indeed, proteins can have outstanding charge transport efficiencies.

While solid-state protein junctions have shown efficient electron transport over lengths that surpass those of conventional organic semiconducting systems, interfacial or contact effects may obscure the intrinsic protein charge transport properties. Therefore, contact resistance (RC) effects need to be quantified and then minimized, which poses a problem if 4-probe geometries cannot be used. Here we show how RC can be extracted quantitatively from the measured junction resistance (RP) by using the extrapolated zero-length resistance (RZLR) and short-circuit resistance (RS). We used AC (impedance spectroscopy) and DC measurements to examine charge transport in junctions of human serum albumin (HSA) and bacteriorhodopsin (bR) films with varying thicknesses. Three contact configurations, Si-Au, Au-EGaIn, and, in a micropore device (MpD), Au-Pd, were compared. While Si-Au and Au-EGaIn junctions exhibit substantial RC that we ascribe to interfacial oxides and electrostatic protein-electrode interactions, MpD effectively eliminates RC, enabling measuring the intrinsic electron transport across HSA and bR films. The exponential length dependence of RP shows a transport decay constant (beta) that varies with interfacial conditions, underscoring the role of contact engineering. By minimizing RC, exceptionally low beta values (0.7 to 1.1 per nm) are found, proving that, indeed, proteins can have outstanding charge transport efficiencies.

The integration of functional proteins into solid-state electronic devices remains a central challenge in molecular bioelectronics due to the fragile nature of protein structures and their complex charge-transport behavior. Here, we present a robust crosswire evaporated top-contact device based on bacteriorhodopsin (bR) single-bilayers (SBL), configured as Au/Cys/bR(SBL)/eC/Au (simplified as Au/bR/eC). The evaporated carbon (eC) top electrode forms a conformal, non-invasive contact that suppresses filament formation and ensures electrical integrity across the crosswire intersecting area (approximate to 200 mu m2). Structural and spectroscopic analyses confirm that the solid-state bR films retain the native absorption spectrum and exhibit functional photocycle activity after electrode deposition, indicating that their native conformation is not significantly altered. Remarkably, electron transport (ETp) through the approximate to 9 nm bR-SBL junctions is temperature-independent within 300 K-10 K, excluding thermally activated hopping, while the length is incompatible with coherent tunneling. Under green illumination, the junctions exhibit a reversible, photo-induced current enhancement (Jgreen/Jdark approximate to 2), ascribed to light-driven conformational changes rather than direct photoexcitation. The Au/bR/eC architecture thus establishes a thermally non-activated, conformationally mediated transport mechanism via a stable, cryo-compatible solid-state protein junction. This work provides a scalable platform for integrating light-responsive biomolecules into future bio-optoelectronic and neuromorphic devices.

The (opto)electronic behavior of semiconductors depends on their (quasi-)free electronic carrier densities. These are regulated by semiconductor doping, i.e., controlled "electronic contamination". For metal halide perovskites (HaPs), the functional materials in several device types, which already challenge some of the understanding of semiconductor properties, this study shows that doping type, density and properties derived from these, are to a first approximation controlled via their surfaces. This effect, relevant to all semiconductors, and already found for some, is very evident for lead (Pb)-HaPs because of their intrinsically low electrically active bulk and surface defect densities. Volume carrier densities for most polycrystalline Pb-HaP films (<1 µm grain diameter) are below those resulting from even < 0.1% of surface sites being electrically active defects. This implies and is consistent with interfacial defects controlling HaP devices in multi-layered structures with most of the action at the two HaP interfaces. Surface and interface passivation effects on bulk electrical properties are relevant to all semiconductors and are crucial for developing those used today. However, because bulk dopant introduction in HaPs at controlled ppm levels for electronic-relevant carrier densities is so difficult, passivation effects are vastly more critical and dominate, to first approximation, their optoelectronic characteristics in devices.

Self-healing (SH) of (opto)electronic material damage can have a huge impact on resource sustainability. The rising interest in halide perovskite (HaP) compounds over the past decade is due to their excellent semiconducting properties for crystals and films, even if made by low-temperature solution-based processing. Direct proof of self-healing in Pb-based HaPs is demonstrated through photoluminescence recovery from photodamage, fracture healing and their use as high-energy radiation and particle detectors. Here, the question of how to find additional semiconducting materials exhibiting SH, in particular lead-free ones is addressed. Applying a data-mining approach to identify semiconductors with favorable mechanical and thermal properties, for which Pb HaPs are clear outliers, it is found that the Cs2AuIAuIIIX6, (X = I, Br, Cl) family, which is synthesized and tested for SH. This is the first demonstration of self-healing of Pb-free inorganic HaP thin films, by photoluminescence recovery. A data-mining approach is used to find self-healing materials for photovoltaic applications. Target ranges of material property combinations are found for candidate materials that can self-heal from damage. Cs2AuIAuIIICl6 and Cs2AuIAuIIIBr6 are successfully synthesized and tested to support the general finding.image

We report continuous wave laser-assisted evaporation (CLE), a thin film deposition technique that yields phase-pure and stoichiometric thin films of halide perovskites (HaPs) from stoichiometric HaP targets. We use methylammonium lead bromide (MAPbBr3) to demonstrate the ability to grow with CLE well-oriented and smooth thin films on various substrates. Further, we show the broader applicability of CLE by preparing films of several other 3D HaP compounds, viz., methylammonium lead iodide, formamidinium lead bromide, and a 2D one, butylammonium lead iodide. CLE is a single-source, solvent-free, room-temperature process that needs only roughing pump vacuum; it allows the deposition of hybrid organic-inorganic compound films without needing post-thermal treatment or an additional organic precursor source to yield the intended product. The resulting films are polycrystalline and highly oriented. All these features, and the fact that one stoichiometric source serves as the target, make for an attractive, potentially scalable dry deposition approach.

Layered 2D halide perovskites are chemically synthesized realizations of quantum well stacks with giant exciton oscillator strengths, tunable emission spectra and very large exciton binding energies. While these features render 2D halide perovskites a promising platform for room-temperature polaritonics, bosonic condensation and polariton lasing in 2D perovskites have so far remained elusive at ambient conditions. Here, we demonstrate room-temperature cavity exciton-polariton condensation in mechanically exfoliated crystals of the 2D Ruddlesden-Popper iodide perovskite (BA)_2(MA)_2Pb_3I_10 in an open optical microcavity. We observe a polariton condensation threshold of P_th=6.76 fJ per pulse and detect a strong non-linear response. Interferometric measurements confirm the spontaneous emergence of spatial coherence across the condensate with an associated first-order autocorrelation reaching g^(1)≈ 0.6. Our results lay the foundation for a new class of room-temperature polariton lasers based on 2D halide perovskites with great potential for hetero-integration with other van-der-Waals materials and combination with photonic crystals or waveguides.

Photosystem I (PSI) is a photosynthetic protein which evolved to efficiently transfer electrons through the thylakoid membrane. This remarkable process attracted the attention of the biomolecular electronics community, which aims to study and understand the underlying electronic transport through these proteins by contacting ensembles of PSI with solid-state metallic contacts. This paper extends published work of immobilizing monolayers of PSI with a specific orientation, by using organophosphonate self-assembled molecules with hydrophilic heads on ultra-flat titanium nitride. Electrical measurements carried out with eutectic GaIn top contacts showed current rectification ratios of up to ~200. The previously proposed rectification mechanism, relying on the protein's internal electric dipole, was inquired by measuring shifts in the work function. Our straightforward bottom-up fabrication method may allow for further experimental studies on PSI molecules, such as embedding them in solid-state, transparent top contact schemes for optoelectronic measurements.

Proteins are attractive as functional components in molecular junctions. However, control-ling the electronic charge transport via proteins, held between two electrodes, requires in-formation on their frontier orbital energy level alignment relative to the electrodes’ Fermi level (EF), which normally requires studies of UV Photoemission Spectroscopy (UPS) with HeI excitation. Such excitation is problematic for proteins, which can denature under stand-ard measuring conditions. Here we use high-sensitivity soft UV photoemission spectroscopy (HS-UPS) combined with Constant Final State Yield Spectroscopy (CFS-YS) to get this in-formation for electrode/protein contacts. Monolayers of the redox protein Azurin, (Az) and its Apo-form on Au substrates, have HOMO onset energies, obtained from CFS-YS, differ by ~ 0.2 eV, showing crucial role of the Cu redox centre in the electron transport process. We find that combined HS-UPS / CFS-YS measurements agree with the Photoelectron Yield Spectroscopy (PYS), showing potential of the HS-UPS + CFS-YS as a powerful tool to char-acterize and map the energetics of a protein-electrode interfaces, which will aid optimizing design of devices with targeted electronic properties, as well as for novel applications.