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Low‐bandgap nonfullerene acceptors (NFAs) offer a unique potential for photovoltaic (PV) applications, such as transparent PV and agrivoltaics. Evaluating each new PV system to achieve the optimum thickness, microstructure, and device performance is, however, a complex multiparametric challenge with large time and resource requirements. Herein, the PV potential of low‐bandgap donor and NFA materials by combining high‐throughput screening and statistical methods is evaluated. The use of thickness gradients (20–600 nm) facilitates the fabrication of more than 2000 doctor‐bladed devices from 24 different low‐bandgap blend combinations. The corresponding power conversion efficiencies varies significantly, from 0.06% to 10.45% across materials and thicknesses. The self‐consistency of the large dataset allows to perform a parameter sensitivity study as well as parameter correlation analysis. These reveal that the choice of materials and energy alignment‐related features (i.e., electron affinity offset, ionization energy offset, bandgap, and energy loss) has the largest influence on final device performance, while processing conditions appear less important for the final efficiencies. Our study demonstrates that high‐throughput experimentation is a perfect match for correlation analyses in order to gain a statistically meaningful understanding of these systems, potentially accelerating the discovery of new materials.

Low-bandgap nonfullerene acceptors (NFAs) offer a unique potential for photovoltaic (PV) applications, such as transparent PV and agrivoltaics. Evaluating each new PV system to achieve the optimum thickness, microstructure, and device performance is, however, a complex multiparametric challenge with large time and resource requirements. Herein, the PV potential of low-bandgap donor and NFA materials by combining high-throughput screening and statistical methods is evaluated. The use of thickness gradients (20–600 nm) facilitates the fabrication of more than 2000 doctor-bladed devices from 24 different low-bandgap blend combinations. The corresponding power conversion efficiencies varies significantly, from 0.06% to 10.45% across materials and thicknesses. The self-consistency of the large dataset allows to perform a parameter sensitivity study as well as parameter correlation analysis. These reveal that the choice of materials and energy alignment-related features (i.e., electron affinity offset, ionization energy offset, bandgap, and energy loss) has the largest influence on final device performance, while processing conditions appear less important for the final efficiencies. Our study demonstrates that high-throughput experimentation is a perfect match for correlation analyses in order to gain a statistically meaningful understanding of these systems, potentially accelerating the discovery of new materials.

Wide band-gap organic solar cells are gaining interest due to their applications in emergent light-harvesting technologies such as underwater photovoltaics, multi-junction solar cells, or indoor photovoltaics. In this work, a combinatorial screening approach is used to explore binary combinations of three wide band-gap donors (PTQ10, PM6, and D18) and three wide band-gap acceptors (PMI-FF-PMI, O-IDFBR, and IO-4Cl) deposited from solution in two solvents (CB and CF). In total, 18 combinations are blade-coated with active layers exhibiting a thickness gradient generating solar cells with 12 different thicknesses. PTQ10:IO-4Cl and PTQ10:O-IDFBR are the most efficient blends with efficiencies of 7.31% and 6.87%, respectively. The voltage loss analysis shows that PTQ10-based devices exhibit the lowest non-radiative voltage losses, whereby the PTQ10:O-IDFBR combination has the lowest voltage loss of all studied blends, with a remarkably high open-circuit voltage (Voc) of 1.35 V. Due to their high performance and Voc, PTQ10:O-IDFBR devices were also studied for indoor light harvesting, achieving an efficiency of 22.6% and a Voc of 1.21 V under 560 lux indoor illumination. To the best of our knowledge, this indoor Voc value is the highest achieved in the field of indoor organic photovoltaics.

We report an easy and low-cost method for the preparation of highly homogeneous electroactive substrates that can be used simultaneously for surface-enhanced Raman spectroscopy (SERS) and electrochemical measurements. The choice of conductive indium tin oxide (ITO) as a substrate is based on its excellent electrical conductivity and transparency. However, its typically high roughness makes the subsequent metal deposition with traditional methods very challenging, making them time-consuming and costly. To circumvent this problem, we developed a simple two-step procedure consisting of first the deposition of a quasi-hexagonal pattern of homogeneously distributed gold nanoparticles (AuNPs) by block-copolymer micellar lithography on ITO. Subsequently, the AuNPs act as seeds for further gold growth by electrodeposition on the pre-patterned ITO substrate. In this way, we reproducibly achieved substrates (>50) with an average gold coverage of (40 ± 5) % and many hot spots due to a small average inter-particle distance of (15 ± 5) nm. These substrates exhibit a strong and homogeneous Raman signal, as determined using 2D maps obtained with the standard Raman tag molecule 4-mercaptobenzoic acid. Moreover, the electrochemical performance of the developed conductive SERS substrates was demonstrated using a Michael addition reaction monitored by Raman scattering. This reaction occurs between the hydroquinone/benzoquinone redox pair and a biologically relevant analyte, but only takes place in one of the redox states of the hydroquinone/benzoquinone system.

Metal halide perovskites (MHPs) are solution-processed materials with exceptional photoconversion efficiencies that have brought a paradigm shift in photovoltaics. The nature of the peculiar optoelectronic properties underlying such astounding performance is still controversial. The existence of ferroelectricity in MHPs and its alleged impact on photovoltaic activity have fueled an intense debate, in which unanimous consensus is still far from being reached. Here we critically review recent experimental and theoretical results with a two-fold objective: we argue that the occurrence of ferroelectric domains is incompatible with the A-site cation dynamics in MHPs and propose an alternative interpretation of the experiments based on the concept of ferroelasticity. We further underline that ferroic behavior in MHPs would not be relevant at room temperature or higher for the physics of photogenerated charge carriers, since it would be overshadowed by competing effects like polaron formation and ion migration.

Most metal halide perovskites (MHPs) which under ambient conditions crystallize in a tetragonal or cubic phase exhibit a fairly linear increase of the fundamental gap with increasing temperature, in frank contrast to other conventional semiconductors. Though valid in general for MHPs, it has been shown for the archetypal perovskite MAPbI3 (MA stands for methylammonium) that such a behavior is due to an almost equal footing of the effects of thermal expansion on the electronic states and the temperature-induced gap renormalization due to the electron–phonon interaction. Here, the influence of the incorporation of small amounts of Cs on the gap renormalization was investigated in two CsxMA1–xPbI3 single crystals (x = 0.05 and 0.1). Strikingly, from ambient to a temperature Ton of 250–280 K, the slope of the linear temperature dependence of the energy gap for both Cs-containing samples is almost half that for pure MAPbI3. Below Ton and within the stability range of the tetragonal phase, the slope recovers the value of MAPbI3. Based on density functional theory calculations, this surprising behavior is explained as being due to the appearance of an additional electron–phonon coupling mechanism ascribed to dynamic tilting of the PbI6 octahedrons. The latter is activated by the translational dynamics of the Cs cations between equivalent potential minima inside the inorganic cage voids, which is unfolded above the onset temperature Ton. These results provide further evidence of the key role that the A-site cation dynamics plays in the optoelectronic properties of this fascinating class of materials.

We present an innovative contactless method suitable to study in-plane thermal transport based on beam-offset frequency-domain thermoreflectance using a one-dimensional heat source with uniform power distribution. Using a one-dimensional heat source provides a number of advantages as compared to point-like heat sources, as typically used in time- and frequency-domain thermoreflectance experiments, just to name a few: (i) it leads to a slower spatial decay of the temperature field in the direction perpendicular to the line-shaped heat source, allowing to probe the temperature field at larger distances from the heater, hence, enhancing the sensitivity to in-plane thermal transport; (ii) the frequency range of interest is typically kHz. This rather low frequency range is convenient regarding the cost of the required excitation laser system but, most importantly, it allows the study of materials without the presence of a metallic transducer with almost no influence of the finite optical penetration depth of the pump and probe beams on the thermal phase lag, which arises from the large thermal penetration depth imposed by the used frequency range. We also show that for the case of a harmonic thermal excitation source, the phase lag between the thermal excitation and thermal response of the sample exhibits a linear dependence with their spatial offset, where the slope is proportional to the inverse of the thermal diffusivity of the material. We demonstrate the applicability of this method to the cases of: (i) suspended thin films of Si and PDPP4T, (ii) Bi bulk samples, and (iii) Si, glass, and highly-oriented pyrollitic graphite (HOPG) bulk samples with a thin metallic transducer. Finally, we also show that it is possible to study in-plane heat transport on substrates with rather low thermal diffusivity, e.g., glass, even using a metallic transducer. We achieve this by an original approach based on patterning the transducer using focused ion beam, with the key purpose of

We report a multi-purpose spectrum-on-demand light source (SOLS), conceived primarily but not exclusively for the multiple and advanced characterization of photovoltaic (PV) materials and devices. The apparatus is a spectral shaper illumination device, providing a tunable and spectrally shaped light beam produced by modulating the intensity and/or wavelength range of a primary light source. SOLS stands out from the state of the art because it produces almost any spectrum on demand and delivers two types of output: a spectrally shaped and spatially homogeneous beam over its cross section for areal illumination or a spatially and spectrally split beam into its wavelength components, a unique capability suited to characterize lateral-tandem (Rainbow) solar cells. The tuneability from broadband to narrowband illumination enables two characterization devices into one, namely, a solar simulator for the determination of the power conversion efficiency and an external quantum efficiency measuring system. We expect the SOLS setup to accelerate material screening, enabling the discovery and optimization of novel multi-component materials and devices, in particular for emergent PV technologies like organic, metal halide perovskites, or multi-junction geometries, as well as novel PV applications such as indoors, building integrated, or agrivoltaics, among others.

The exceptional optoelectronic properties of metal halide perovskites (MHPs) are presumed to arise, at least in part, from the peculiar interplay between the inorganic metal-halide sublattice and the atomic or molecular cations enclosed in the cage voids. The latter can exhibit a roto-translative dynamics, which is shown here to be at the origin of the structural behavior of MHPs as a function of temperature, pressure and composition. The application of high hydrostatic pressure allows for unraveling the nature of the interaction between both sublattices, characterized by the simultaneous action of hydrogen bonding and steric hindrance. In particular, we find that under the conditions of unleashed cation dynamics, the key factor that determines the structural stability of MHPs is the repulsive steric interaction rather than hydrogen bonding. Taking as example the results from pressure and temperature-dependent photoluminescence and Raman experiments on MAPbBr[Formula: see text] but also considering the pertinent MHP literature, we provide a general picture about the relationship between the crystal structure and the presence or absence of cationic dynamic disorder. The reason for the structural sequences observed in MHPs with increasing temperature, pressure, A-site cation size or decreasing halide ionic radius is found principally in the strengthening of the dynamic steric interaction with the increase of the dynamic disorder. In this way, we have deepened our fundamental understanding of MHPs; knowledge that could be coined to improve performance in future optoelectronic devices based on this promising class of semiconductors.

In this study, nanocrystals of antiferromagnetic Cr2O3 are shown via Raman spectroscopy to display peculiar lattice dynamics in terms of phonon softening and the occurrence of an exceptionally strong spin-phonon coupling. This effect, which is observed to persist well above the onset of the antiferromagnetic ordering temperature, is ascribed to locally correlated spin fluctuations due to the modulation of the magnetic exchange interactions as the chromium atoms oscillate about their equilibrium position. It is found that the spin-phonon coupling strength is governed by the competing antiferromagnetic and ferromagnetic interactions, where changes in the surface spin configuration can also play a crucial role. Overall, this work proves the size dependence of the interplay between the crystalline and magnetic structures in 3D antiferromagnets varying the surface-to-volume ratio and helps establish the fundamentals for a spin-phonon coupling engineering at the nanoscale via a simple route in a very stable and easy to synthesize material. More importantly, it demonstrates the possibility of coupling phononic excitations with the magnetization dynamics at room temperature, offering a highly prospective nanomaterial for the design of novel magnonic devices.

While multi-junction geometries have the potential to boost the efficiency of organic solar cells, the experimental gains yet obtained are still very modest. This work proposes an alternative spectral splitting device concept in which various individual semiconducting junctions with cascading band gaps are laid side by side, thus the name RAINBOW. Each lateral sub-cell receives a fraction of the spectrum that closely matches the main absorption band of the given semiconductor. Here, simulations are used to identify the important material and device properties of each RAINBOW sub-cell. Using the resulting design rules, three systems are selected, namely PBDB-T-2F:IO-4Cl, PBDB-T-2F:Y6 and PTB7-Th:COTIC-4F, and their potential as sub-cells in this geometry is experimentally investigated. With the aid of a custom built setup that generates spectrally spread sunlight on demand, the simulations are experimentally validated, showing that this geometry can lead to a reduction in thermalization losses and an improvement in light harvesting, which results in a relative improvement in efficiency of 46.6% with respect to the best sub-cell. Finally, a working proof of concept monolithic device consisting of two sub-cells deposited from solution on the same substrate is fabricated, thus demonstrating the feasibility and the potential of the RAINBOW solar cell concept. This article is protected by copyright. All rights reserved.

The dissipation of heat generation has been one of the largest obstacles in the design of semiconductor devices and reducing the thermal conductivity is vital for improving thermoelectric efficiency. This work focuses on the Bi doping effect on ZnO, and ZnO:Al thin films produced by magnetron sputtering with thickness varying between 500 and 900 nm. The approach introduces Bi ions, a higher mass element, into the ZnO metal-oxide matrix, to hinder phonon-mediated heat conduction and, consequently, reduce thermal conductivity. Atom probe tomography (APT) was employed to survey Bi doping distribution in ZnO:Al:Bi and ZnO:Bi thin films and to study the morphology of the grain boundaries. The thermal properties of the thin films were measured by frequency-domain thermoreflectance. Based on thermal conductivity results, it is concluded that the doping of ZnO films with Al has a significant effect on thermal conductivity, being reduced from 6.0 W m−1 K−1 in its undoped state to 3.3 W m−1 K−1 for ZnO with ∼3 at.% of Al, mainly due to alloy scattering of phonons in the wurtzite cell. Further doping with Bi contributes to a slight reduction in the thermal conductivity of ZnO:Al.Bi films (2.9 W m−1 K−1), due to grain boundary scattering by Bi/Bi2O3 phases. This result is understood as the confluence of two counteracting effects. On the one hand, the thermal conductivity of the film decreases because Bi, unlike Al, is segregated to grain boundaries and does not substitute Zn in the wurtzite crystal lattice, which is unequivocally demonstrated by APT results. On the other hand, the simultaneous presence of Al and Bi triggers a morphological change with the film's microstructure becoming more columnar. This change in microstructure from 3D island growth in ZnO:Al and ZnO:Bi to a more regular columnar structure in ZnO:Al,Bi limits further reduction in the thermal conductivity.

In any solar cell, the exploitable spectral range of sunlight is limited by the band gap of the active photovoltaic material, which in the case of silicon is 1.1 eV (roughly 1100 nm). Thus, nearly half of the solar spectrum remains unabsorbed, namely, the near infrared (NIR) part. To alleviate this situation, a common alternative to photoelectric conversion relies on the mechanism of plasmon-enhanced internal photoemission of hot electrons at metal/semiconductor heterostructures. Photons with energies below the gap of the semiconductor are absorbed by the metal, launching surface plasmons, which, upon relaxation, produce a photocurrent of hot carriers into the semiconductor.

The transparency of silicon in the infrared region enables the design of nano/microstructures for implementation in devices to harvest the infrared (IR) part of the solar spectrum. Herein we report a strategy that uses arrays of inverted silicon pyramids covered with a thin gold film, which exhibit substantial light absorption in the infrared spectral range (below the gap of Si). The absorption stems from the resonant excitation at infrared wavelengths of surface-plasmon polaritons at the metal/dielectric interface mainly by tuning size and separation of the inverted pyramids. The array-parameter optimization proceeded by iteration of the calculation and measurement of the infrared response using finite difference time-domain simulations and Fourier-transform IR spectroscopy, respectively. We analyse the calculated near-field distributions specifically looking for the presence of hot spots, i.e. nano-sized regions of very high concentration of the electronic charge and strong electromagnetic field enhancement, and discuss their potential for hot-electron generation. We show two fabrication routes for this kind of metal/silicon metamaterial either by photolithography or scalable nanoimprint techniques for a seamless integration in optoelectronic fabrication processes.

The fabrication of multifunctional switches is a fundamental step in the development of nanometer-scale molecular spintronic devices. The anchoring of active organic radicals on gold nanoparticles (AuNPs) surface is little studied and the realization of AuNPs-based switches remains extremely challenging. We report the first demonstration of a surface molecular switch based on AuNPs decorated with persistent perchlorotriphenylmethyl (PTM) radicals. The redox properties of PTM are exploited to fabricate electrochemical switches with optical and magnetic responses, showing high stability and reversibility. Electronic interaction between the radicals and the gold surface is investigated by UV-vis, showing a very broad absorption band in the near-infrared (NIR) region, which becomes more intense when PTMs are reduced to anionic phase. By using multiple experimental techniques, we demonstrate that this interaction is likely favored by the preferentially flat orientation of PTM ligands on the metallic NP surface, as confirmed by first-principles simulations.

Direct piezoelectric force microscopy (DPFM) is employed to examine whether or not lead halide perovskites exhibit ferroelectricity. Compared to conventional piezoelectric force microscopy, DPFM is a novel technique capable of measuring piezoelectricity directly. This fact is fundamental to be able to examine the existence of ferroelectricity in lead halide perovskites, an issue that has been under debate for several years. DPFM is used to detect the current signals, i.e. changes in the charge distribution under the influence of the scan direction and applied force of the atomic force microscope (AFM) tip in contact mode. For comparison, (i) we use DPFM on lead halide perovskites and well-known ferroelectric materials (i.e. periodically poled lithium niobate and lead zirconate titanate); and (ii) we conduct parallel experiments on MAPbI3 films of different grain sizes, film thicknesses, substrates, and textures using DPFM as well as piezoelectric force microscopy (PFM) and electrostatic force microscopy (EFM). In contrast to previous work that claimed there were ferroelectric domains in MAPbI3 perovskite films, our work shows that the studied perovskite films Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3 and MAPbI3 are ferroelectricity-free. The observed current profiles of lead halide perovskites possibly originate from ion migration that happens under an applied electrical bias and in strained samples under mechanical stress. This work provides a deeper understanding of the fundamental physical properties of the organic–inorganic lead halide perovskites and solves a longstanding dispute about their non-ferroelectric character: an issue of high relevance for optoelectronic and photovoltaic applications.

The complex electron−phonon interaction occurring in bulk lead halide perovskites gives rise to anomalous temperature dependences, like the widening of the electronic band gap as temperature increases. However, possible confinement effects on the electron−phonon coupling in the nanocrystalline version of these materials remain unexplored. Herein, we study the temperature (ranging from 80 K to ambient) and hydrostatic pressure (from atmospheric to 0.6 GPa) dependence of the photoluminescence of ligand-free methylammonium lead triiodide nanocrystals with controlled sizes embedded in a porous silica matrix. This analysis allowed us to disentangle the effects of thermal expansion and electron−phonon interaction. As the crystallite size decreases, the electron−phonon contribution to the gap renormalization gains in importance. We provide a plausible explanation for this observation in terms of quantum confinement effects, showing that neither thermal expansion nor electron−phonon coupling effects may be disregarded when analyzing the temperature dependence of the optoelectronic properties of perovskite lead halide nanocrystals.