Metal halide perovskites are a leading contender to disrupt not only terrestrial photovoltaic (PV) markets, but also the proliferating space PV markets. This is due to their impressive power conversion efficiencies, potentially low cost, and adaptability to flexible architectures. Here we assess the stability of three perovskite systems; a mixed Pb-Sn perovskite, and two mixed cation-triple halide systems. In all cases high tolerance to proton irradiation was observed. However, in the case of the mixed Pb-Sn system, irreversible decomposition of the perovskite along with the increased prevalence of defects was observed with thermal cycling. In the case of the mixed cation triple halides remarkable stability was demonstrated, in addition to self-healing, the results of which will be described here.

Improving the stability of lead halide perovskite (LHP) solar cells is a major challenge towards their industrialization. It has been shown that moisture induces changes in the global Perovskite Solar Cell (PSC) performances. Here we investigate the chemical and structural evolution of hybrid cation mixed halide perovskite after aging under controlled humidity. We perform Photoluminescence, Energy Dispersive X-ray Spectroscopy in a STEM, and Cathodoluminescence analyses of triple cation perovskite (Cs0.05MA0.45FA0.5Pb(I0.83Br0.17)3) integrated into an efficient solar cell. We observe optical and chemical variations correlated with morphology changes at a microscopic scale, and we analyze the structural changes of the perovskite layer.

In this contribution, we use spectrally resolved and quantitative photoluminescence measurements to parse voltage losses in CdSeTe films and finished devices. We show that sub-bandgap features, in part due to arsenic doping, are responsible for a significant decrease in the thermodynamic voltage limit Voc,ideal. Nevertheless, thanks to excellent material quality and interface passivation, the internal voltage iVoc (i.e., quasi-Fermi-level splitting with QFLS=q×iVoc) of finished devices approaches 1000 mV, in agreement with the high minority-carrier lifetimes measured. The selectivity of the device, and in particular of the back hole contact, is thus the main limitation in these devices.

The external quantum efficiency (EQE) or associated spectral response is widely used to evaluate the performance of photovoltaics, light emitting diodes, photodetectors, photodiodes, semiconductor lasers, laser-induced refrigeration of solids etc. For photovoltaic (PV) devices, The EQE is used to determine the spectral mismatch correction that is used to convert a performance measurement from a non-ideal simulator spectrum to a standard spectrum in PV device calibrations. Moreover, EQE can provide important insight into the physics of a PV device. For instance, the EQE shape can be used to infer mechanisms limiting the performance of the device. However, EQE measurements of full-size PV modules remain a challenge in the PV community due to rare availability of reliable module QE measurement tools worldwide and the size and complexity of module architecture that comprises several cells connected in strings (series or/and parallel). Here, we use a customized nondestructive tool made of high-power light emitting diodes to perform high-throughput EQE measurements on PV modules. Circuit simulations show that the measurement system can safely be used to measure both crystalline silicon and thin film-based PV modules with series connected cells without the risk of damage through reverse bias. In addition, EQE mapping combined with electroluminescence show a strong correlation and provide a way to determine both spatial non-uniformity of the spectral response and defects/degradation effects across the module.

We employ Kelvin-probe force microscopy (KPFM) and photoconductive-atomic force microscopy (pc-AFM) to comprehensively evaluate the nanoscale transformations in optoelectrical properties in multi-cation metal halide perovskites. We quantify the changes in photocurrent and photovoltage for both dual-cation and quad-cation perovskite. The superior electrical performance observed in quad-cation perovskite, lent by Rb+ cation, will be discussed in detail. An in-depth analysis of photoactivity within grains and grain boundaries will be shared. Further, a mechanism for charge carrier transport is proposed through two types of GBs- with defects, and with defect passivation in dual and quad-cation perovskite, respectively.

Metal-halide perovskites are emerging as an intriguing class of semiconductors with significant potential for photovoltaics. Here, several perovskites are discussed that have been assessed via various experimental techniques to determine the effects of their composition, dimensionality, and structural stability on hot carriers and polaron formation. It will be shown that polarons formed in these systems are strongly affected by the binding energy and nature of the excitons in the materials. Notably, the hot carrier dynamics in perovskites is strongly affected by their low thermal conductivity, which inhibits the dissipation of heat in the material.

We present a study on the role and optimization of diffraction gratings used as back reflector/scatterer in multiresonant GaAs ultrathin solar cells. We show the influence of parameters variation for the grating and for the pattern on the diffraction efficiencies. With an optimized square pattern, we show a record-high absorption of 92.5% in a 100 nm-thick GaAs absorber. Accounting for parasitic absorption, the estimated short-circuit current is 26.4 mA/cm2. We also discuss routes towards even higher currents by breaking the degeneracy of the modes with non-symmetric structures.

Using the reciprocal space, two types of structures are simple to identify: simple periodic (photonic crystals), which have high diffractive efficiencies but sparse resonances (narrow-band), and random structures, with a continuous reciprocal space (broadband) but suffering from low diffraction efficiencies. A third type, quasirandom structures, lies in between; these provide high diffractive efficiency over a target wavelength range, which is broader than simple photonic crystals but narrower than a random structure. These structures are promising for ultrathin solar cells due to their broader nature. We present our numerical work towards evolving simple photonic crystals in quasirandom structures, and our fabrication approach based on polymer-blend lithography, with initial results on solar cells.

Photovoltaic (PV) solar cells are designed to efficiently absorb solar photons but convert only a limited proportion of them into electricity. The remaining energy is converted into heat, which in turn, heats the entire solar modules up to 50-60 °C under real operating conditions. This is detrimental to both their power conversion efficiency and lifetime. Recently, there has been a growing interest in the so-called radiative sky cooling (RSC) strategy. This approach consists in optimizing the thermal radiation of cells or modules - with the help of photonic structures - by taking advantage of the atmospheric transparency in the 8-13 μm range. Although some basic studies predict cooling of more than 10°C on silicon devices, they remain insufficient to assess the potential of this technique for various PV technologies directly from their material properties. Using COMSOL Multiphysics, we are working on a fully coupled model of silicon solar cells in order to predict their opto-electro-thermal behaviour from the bottom-up (i.e. using only material properties as an input). This enables us to study various photonic pathways for enhanced radiative sky cooling. Our work also shows the importance of moving towards fully coupled models to accurately predict the temperature and electrical output under real conditions.

Emerging photovoltaic concepts (hot-carrier, multi-exciton generation and intermediate-band solar cells) have so far not been able to reach their promised efficiencies. This is partly because they require power densities that are difficult to achieve, even with concentrated sunlight illumination. Besides the need for novel materials, it is therefore critical to develop strategies to maximize the power absorbed per unit volume. In this presentation, I emphasize the key role light trapping can play in this regard and discuss theoretical and practical limitations of broadband absorption enhancement. Focusing on hot-carrier solar cells, I show how thermalization can be strongly suppressed in thin, quantum layers, and the challenges in implementing such absorbers. I also suggest alternative designs that can partly alleviate the thermalization constraints.

We present the first steps toward the development of MoS2/Si heterojunctions photovoltaics, essentially for integrated photonic devices applications. Therefore, we conjugate numerical device simulation, optical and structural characterizations, and density functional theory calculations. Through numerical device simulation, we show the potential of such solar cells, with attainable power conversion efficiencies of about 20%. Optical and structural characterizations of thin 2H-MoS2 layers deposited on SiO2 80nm/Si (001) substrates provides a path for the optimization of the 2D MoS2 material. With DFT calculations, we open the door for the optimization of the MoS2/Si interface, which is crucial for the device performances.

The field of thermophotovoltaics offers a direct method to translate the heat generated as a byproduct of other standard energy generation techniques into usable electricity. This requires an emitted spectrum tailored to produce the maximum possible amount of light in a wavelength regime which is utilizable by a given photovoltaic cell. In this work, we investigate the efficiency of coating/substrate emitters using ~50 materials with melting points >2000C. We show combinations including oxide/refractory metal coating/substrate pairs which result in an FOM of >40% at 1800C, demonstrating their potential to greatly outperform currently available thermophotovoltaic devices.

During the past decades, much research was directed toward studying energy storage materials such as palladium. Such materials can store hydrogen like a sponge providing lightweight, high-density hydrogen sources that can be used for vehicles and mobile applications. In this paper, we make use of these lightweight storage materials for designing a solid-state negative hydrogen ion source that can be controlled by light. We propose a metasurface design of GaAs patches on a palladium substrate that releases hydrogen atoms and when excited with light, the electrons tunnel from the GaAs to the H atoms producing negative hydrogen ions. The mechanism of our device is modeled using a transfer matrix approach. This work provides for the first time the possibility of having a photo controlled solid-state negative hydrogen ion source that can impact both accelerator-based ion sources as well as energy storage applications.

Investigations of photovoltaic devices and semiconductors are essential to enhance the efficiency of preparation methods as well as their electronic and optical properties. We present a powerful combination of time-resolved photoluminescence microscopy with a spectrometer, which results in a powerful toolbox for researcher. This combination of microscopic (e.g., FLIM, PLIM or carrier diffusion imaging) and spectroscopic methods like wavelength dependent emission scanning enables investigations of photophysical properties of semiconductors, nanoparticles and nanostructures on a whole new level.