Symposium FB
ABSTRACTS
Session FB-1 Photovoltaics
FB-1.A Thin-film photovoltaics and III.V solar cells
FB-1.A:IL01 Modelling Surfaces and Interfaces in Thin-Film Photovoltaics: Extended Defect Reconstructions in Antimony Selenide and Beyond
K.P. McKENNA, School of Physics, Engineering and Technology, University of York, York, UK
Antimony selenide (Sb2Se3) and sulfoselenides have emerged as promising materials for application as solar absorbers in thin-film photovoltaic and photoelectrochemical cells with device efficiencies now in excess of 10%. By employing density functional theory calculations to model the structure and properties of a wide range of extended defects we predict that (in the absence of point defects) surfaces and grain boundaries in Sb2Se3 and Sb2S3 are unusually free of deep gap states associated with dangling bonds [1,2]. The reason is that extended defects undergo a facile reconstruction where undercoordinated atoms reconfigure to restore their coordination and eliminate associated defect states within the band gap. Associated with the reconstruction of extended defects we predict significant long-range strain fields which have been confirmed by scanning transmission electron microscopy [3]. At the end of this talk I will present preliminary results for some closely related anisotropic semiconductors that are also found to exhibit a similar tendency for facile reconstruction.
[1] R.E. Williams et al, ACS Appl. Mater. & Inter. 12, 21730 (2020). [2] K.P. McKenna, Adv. Electron. Mater. 7, 2000908 (2021). [3] R.A. Lomas-Zapata et al, Phys. Rev. X Energy 3, 013006 (2024).
FB-1.A:IL02 The Nanoscale Landscape Dictates Performance in Perovskite Solar Cells
M. ANAYA, Institute of Materials Science of Seville, University of Seville, Seville, Spain
Halide perovskites hold great promise for affordable, high-performance optoelectronics. Yet, their remarkable efficiencies emerge from materials that are far from structurally perfect. Nanoscale compositional gradients, local strain fields and defect clusters coexist within the same device, and their impact on stability and performance remains only partially understood. In this talk, we show how the nanoscale landscape governs charge generation, recombination and long-term degradation in perovskite solar cells. By combining synchrotron nanoprobe X-ray microscopy with correlative optical spectroscopy, we resolve structure-property relationships with sub-100 nm sensitivity. Our results show that perovskites can efficiently “adapt” to imperfections, explaining their unexpected defect tolerance compared to conventional semiconductors. Moreover, we demonstrate spatially resolved pseudo-JV mapping, enabling us to extract key device metrics while directly identifying nanoscale degradation pathways. By comparing different device architectures, we highlight design principles that suppress failure modes at the early stages. These insights contribute to a more rational approach to improving reliability and durability in next-generation perovskite photovoltaics.
FB-1.A:L03 Comprehensive Study on the Long-Term Degradation Behavior of Perovskite Solar Cells
M.I. HOSSAIN, YONGFENG TONG, B. AISSA, Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University (HBKU), Qatar Foundation, Doha, Qatar
The power conversion efficiency of perovskite solar cells (PSCs) is nearly equivalent to that of photovoltaic systems. Operational and long-term stability are crucial for commercialization. Stability assessments are frequently unstandardized and transient, rendering results incomprehensible. Perovskite solar cells possess distinctive characteristics; thus, assessing their stability may necessitate the alteration of criteria. We investigate the influence of storing on the aging of perovskite solar cells over a three-year period. Stability assessments are conducted on glass/FTO/compact-TiO2/mesoporous-TiO2/perovskite/Spiro-OMeTAD/Au solar cell devices. ToF-SIMS and XRD tests indicate that the power conversion efficiency (PCE) of perovskite solar cells maintained in N2 glove boxes diminishes from 17% to 8% over three years as a result of layer disintegration. Notably, lead (Pb) diffusion towards the metallic contact predominates with time. Furthermore, photoluminescence studies indicate that defects caused by ion migration significantly diminish the emission spectrum of the perovskite layer. Our findings enhance our comprehension of PSC longevity and facilitate the development of large-scale PSCs for commercial use.
FB-1.A:L04 DFT and SCAPS-1D Insights into Strain-engineered Performance Enhancement of CsSiBr₃ Solar Cells
S. TOUROUGUI, Group of Semiconductors and Environmental Sensor Technologies Energy Research Center, Faculty of Sciences, Mohammed V University in Rabat, Rabat, Morocco
The development of lead-free absorber materials for photovoltaics is crucial for combining performance and environmental sustainability. Here, we study the inorganic perovskite CsSiBr3 using DFT and SCAPS-1D simulations to examine the effect of triaxial strain on its structural, electronic, and photovoltaic properties. The band gap can be tuned from 0.65 eV (-6% compressive) to 1.35 eV (+6% tensile), enabling a transition from quasi-metallic to semiconducting behavior. Tensile strain enhances optical absorption and carrier collection. Device simulations (FTO/TiO2/CsSiBr3/MoO3/Au) show that the band gap widening increases Voc (0.63 → 1.01 V) and fill factor (83.1 → 87.9%), while Jsc decreases (43.6 → 29.2 mA/cm²), leading to PCE improvement from 23.2% to ~26% under 6% tensile strain. These results highlight CsSiBr3 as a promising, environmentally friendly absorber for next-generation solar cells.
FB-1.A:L05 Silver and Sodium Incorporation into Wide Bandgap CZTS Absorbers on Transparent Back Electrodes and their Application in Kesterite/c-silicon Tandem Solar Cells: Experiments and Simulations
N. ENNOUHI1,2, S. AMMARI2, Y. CHOUIMI2, A. ER-RFYG1,2, M. EL YDRISSI3, N. BEN AFKIR2, Z. SEKKAT1,2, 1Department of Chemistry, Faculty of Sciences, University Mohammed V in Rabat, Rabat, Morocco; 2Optics and Photonics Center, Moroccan Foundation for Advanced Science & Innovation & Research, MAScIR-UM6P, Ben Guerir, Morocco; 3INNOVX, Mohammed VI Polytechnic University, Hay Moulay Rachid, Ben Guerir, Morocco
Kesterite solar cells have emerged as promising top subcells for tandem integration with silicon solar cells. However, producing high-quality kesterite absorbers on transparent substrates remains challenging. This study examines the combined effects of silver (Ag) alloying and sodium (Na) doping on copper zinc tin sulfide (CZTS) thin films deposited on fluorine-doped tin oxide (FTO) using the sol–gel method. X-ray diffraction revealed improved crystallinity and phase purity, while Raman spectroscopy showed a more ordered structure with reduced Cu/Zn disorder and defect density after Ag incorporation. Optical analysis indicated a slight bandgap increase from 1.53 to 1.57 eV. Finite-difference time-domain (FDTD) simulations modeled the optical transmission of the FTO/CZTS/CdS/ZnO/ITO stack, and SCAPS-1D simulations evaluated a crystalline silicon (c-Si) bottom subcell under the transmitted light. The simulated tandem device reached an efficiency of 14.5%, limited by low transmittance and moderate CZTS performance (7.8%). These findings confirm that Ag improves CZTS film quality on transparent electrodes, though further optical and structural optimization is required for efficient tandem solar cells.
FB-1.A:IL06 Tin-based Perovskite Solar Cells and Design of Tandem Cells
SHUZI HAYASE, The University of Electro-Communications, Tokyo, Japan
The efficiency of the lead halide perovskite solar cell (Pb-PVK-PV) is now over 27% and close to the theoretical efficiency because the bandgap is about 1.55 eV. Tin halide-based perovskite solar cells (Sn-based-PVK-PV) follow the Pb-PVK-PV. The Sn-based-PVK-PV covers the bandgap from 1.2 eV to 2.0 eV which include the best bandgap of 1.4 eV for single junction solar cells. In addition, they are useful as the bottom cells of all-perovskite tandem solar cells. The Sn-based-PVK-PV include lead-free Sn-PVK-PV and SnPb-alloyed-PVK-PV whose efficiency is 17.1% and 24.5%, respectively. The efficiency enhancement of Sn-based PVK-PV will be discussed from defect density, and band-offset. The other important research item is stability. The stability was improved by optimizing hole transport layer, perovskite layer and electron transport layer structures. The discussion is focused on suppressing ion diffusions caused by residual solvents in each layer. Finaly, all-perovskite tandem solar cells consisting of Pb-PVK-PV (Top cell), interconnecting layer and SnPb-PVK-PV (Bottom cell) are reviewed, where Pb-free perovskite tandem solar cells will be included.
FB-1.A:IL07 Next Generation III-V Semiconductor Nanowire Solar Cells: Advantages and Challenges
N. LOVERGINE, Dept. of Innovation Engineering, Univ. of Salento, Lecce, Italy
Solar cells (SCs) based on dense arrays of III-V nanowires are being considered strong candidates for the fabrication of high power conversion efficiency (PCE) photovoltaic devices at reduced costs. However, III-V nanowire SCs (NWSCs) reported so far have not confirmed theoretical expectations, their PCE figures remaining well below 18% under 1-sun illumination. This talk will present an innovative strategy to overcome current NWSC limitations through the use of intermediate-band gap semiconductors (IBGSs), namely GaNAs and related dilute-nitride III-V (III-N-V) compounds, as nanowire absorbing materials. This approach combines the multi-band absorption functionality of IBGSs with advantages associated with NWSCs, i.e. the super-absorptive properties of nanowire arrays and reduced volumes of active materials; very high PCEs are expected for such nanowire-based intermediate band SCs. Their practical realization requires however, suitably designed core-multishell radial junction nanowire heterostructures: perspective nano-device architectures will be described. The potentials of and challenges facing current nanowire self-assembly technologies for the fabrication of the proposed III-N-V based nanowire IBSCs will be discussed, and results on the use of MOVPE technology presented.
FB-1.B Organic, dye-sensitised and nanoparticle photovoltaics
FB-1.B:IL08 Towards Three-band Optoelectronics
I. RAMIRO, Electronic Engineering Department, Universitat Politècnica de Catalunya, Spain
The outstanding technological advances enabled by semiconductors in the last decades have relied on their hallmark characteristic: two electronic bands —the conduction and valence bands (CB and VB)— separated by a forbidden energy gap, which enables electrical and optical access to two distinct electronic populations: electrons in the CB and holes in the VB. With a third narrow energy band —the ambipolar band (AB)— in between the VB and the CB, 3-band materials (3BM) emerge as a new paradigm of semiconductors with expanded optoelectronic properties. 3BMs feature three energy gaps (one between each pair of bands) and three electronic populations (one in each band). Such properties unlock groundbreaking 3-band optoelectronic applications, such as high efficiency solar cells, switches for all-optical communications, multi-color lasing, or circuital elements for a 3-state digital logic {0/1/2}. We will make an introduction to 3-band optoelectronics, with especial emphasis on solar cells, and make the case that quantum-dot-in-perovskite (a new class of composite-material family in which colloidal quantum dots are embedded in a perovskite semiconductor matrix) is a promising platform for developing the first practical 3BMs.
FB-1.B:IL09 Combining Perovskites with Silicon for Dual- and Triple-junction Photovoltaics
S. DE WOLF, King Abdullah University of Science and Technology (KAUST), Saudi Arabia
In this presentation I will discuss the multiple ways how monolithic perovskite/silicon tandem solar cells can be fabricated, built from textured silicon heterojunction solar cells, via solution or hybrid processing of the perovskite top cell. Such tandems are instrumental to increase the power density of solar panels for terrestrial applications, but also for applications where high power-to-weight ratios are important. This will be followed by a discussion how the energy yield can be further increased via triple-junction tandems. In all cases, bulk and contact passivation of the perovskites are instrumental to obtain a high performance but also enhanced stability, which can be obtained through a range of molecular additive engineering strategies.
FB-1.B:IL10 Optical Approaches to Modify Radiative Recombination and increase the Open Circuit Voltage in Perovskite and Organic Solar Cells
J. MARTORELL, ICFO-The Institute of Photonic Sciences, Castelldefels, Barcelona, Spain
Several years ago Yablonovitch1 proposed that a forbidden photonic band overlapping the electronic band edge in semiconductor-based devices could lead to a rigorous inhibition of the spontaneous emission providing a path to overcome the limiting performance for semiconductor devices, among them, solar cells. In solar cells such photon emission restriction can lead to a reduction of the Boltzmann losses which would imply a gain in open circuit voltage (Voc). When photon emission and the sunlight absorption cones are matched, Boltzmann losses would vanish setting a power conversion efficiency limit for single junction solar cells well above the limit established by the detailed balance. Here, we report on two different optical configurations that are applied to angular restrict photon emission in organic and perovskite solar cells. We demonstrate that photon emission is inhibited leading, in the case of the organic cells, to the ultimate power conversion efficiency for the cells based on the particular configuration and organic blend being considered. A fully optical control exerted on radiative recombination is demonstrated to provide Voc variations as high as several tens of mV. 1. Yablonovitch, E. Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Phys Rev L
FB-1.C Multiple energy level and light trapping devices
FB-1.C:IL11 Solar Innovations: New Materials for Unconventional Photovoltaic Applications
A. HIN-LAP YIP, Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong, China
This presentation discusses innovative solar energy technologies, focusing on advanced materials and device engineering to expand photovoltaic applications beyond conventional uses. Breakthroughs in printable perovskite and organic solar cells, including tandem configurations and transparent photovoltaics, demonstrate high efficiency, scalability, and adaptability for diverse environments such as urban buildings, agriculture, marine and space systems. Using advanced modeling techniques like high-throughput optical simulations, solar cell architectures can be optimized for performance and integration. Such printable PV technologies with low production costs also enable affordable solar films for electricity generation in rural areas, addressing global energy access challenges. Supported by the UNESCO-endorsed “Fostering Innovation for Resilience and Sustainable Transformation” (FIRST) programme, these innovations align with the UN’s Sustainable Development Goals, fostering international collaboration and capacity building. These advancements emphasize scalable production, cost-effectiveness, and long-term stability, paving the way for broader photovoltaic applications and supporting a sustainable energy transition toward global carbon neutrality goals.
FB-1.C:IL12 Organic Solar Cells - The Path to Commercial Success
K. LEO, IAPP, TU Dresden, Dresden, Germany
Carbon-based organic semiconductors have many potential advantages, such as easy large-area fabrication on flexible substrates, a wide variety of abundant materials, low cost, and an extremely low CO2 footprint.
Nevertheless, in contrast to organic light-emitting diodes (OLEDs), organic solar cells have so far found little commercial application. However, organic solar cells have recently made significant progress, achieving record efficiencies of over 20%. In this talk, I will present an overview of the key features of organic solar cells and recent developments in the field. I will discuss key innovations to achieve broad success for organic solar cells even in a very competitive market. For instance, I will discuss improved designs which avoid the bulk heterojunction and thus achieve more simple fabrication and improved stability. Furthermore, I will discuss new approaches for doping in transport and recombination layers which can lead to significantly improved optical designs.
FB-1.C:IL13 Spiro-Phenoxazine: A Novel Building Block for Stable and Efficient Perovskite Solar Cells
J. URIETA-MORA1,2, SEUNG JU CHOI3, JAEKI JEONG4, S. ORECCHIO2, I. GARCÍA-BENITO2, J. CALBO5, M. PÉREZ-ESCRIBANO5, S.M. ZAKEERUDDIN4, A. MOLINA-ONTORIA1, E. ORTÍ5, N. MARTÍN1,2, M. GRÄTZELD4, 1Departamento Química Orgánica, Facultad C. C. Químicas, Universidad Complutense de Madrid, Madrid, Spain; 2IMDEA-Nanociencia, Ciudad Universitaria de Cantoblanco, Madrid, Spain; 3Ulsan Advanced Energy Technology R&D Center, Korea Institute of Energy Research, Ulsan, Republic of Korea; 4Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; 5Instituto de Ciencia Molecular, Universidad de Valencia, Paterna, Spain
Perovskites solar cells (PSCs) have emerged, since 2009, as the most promising technology to replace/complement crystalline silicon PV. Outstanding results of PCE up to 26.7 % have been obtained using perovskites (eg. MAPbI3) in just a few years of research. The continuous improvement of the efficiency in PSCs has been achieved using commercially available spiro-OMeTAD as hole-transporting material (HTM). However, spiro-OMeTAD is an expensive material due to its difficult purification and multi-step synthetic protocols (in harsh conditions) which limits its future use in large-scale applications. As a consequence, great efforts in the synthesis and characterization of alternative organic low-cost molecules for its application as HTMs have been reported in the recent years, including PAH-based, spiro-containing or dopant-free materials.[1] Our research group reported two doped-HTMs based on electron-rich spiranic scaffolds, namely, spiro-POZ and spiro-PTZ which exhibit a similar performance of the reference material and improved long-term stability (more than 300 days of exposure to ambient conditions and more than 1200 h under continuous 1 sun illumination) in sharp contrast with the reference of spiro-OMeTAD.[2] Motivated by these excellent results, we have designed four new derivatives based on spiro-PTZ functionalized with asymmetric diphenylamine units that have been incorporated in PSCs improving the PCE of the devices up to 25.75%, surpassing clearly the power conversion efficiency and stability of spiro-OMeTAD. Furthermore, large area mini module (25 cm2) also shows an outstanding PCE above 22%, pointing spiro-PTZ derivatives as one of the most efficient HTMs reported in bibliography.[3]
[1] J. Urieta-Mora, I. García-Benito, A. Molina-Ontoria, N. Martín, Chem. Soc. Rev. 2018, 47, 8541-8571. [2] J. Urieta-Mora, I. García-Benito, L.-A. Illicachi, J. Calbo, J. Aragó, A. Molina-Ontoria, E. Ortí, N. Martín, M. K. Nazeeruddin, Sol. RRL 2021, 5, 2100650. [3] J. Urieta-Mora, S.-J. Choi, J. Jeong, S. Orecchio, I. García-Benito, M. Pérez-Escribano, J. Calbo, L. Zheng, M. Byun, S. Song, G.-H. Kim, S.-M. Zakeeruddin, S.-Y. Yoon, Y. Jo, A. Molina-Ontoria, E. Ortí, N. Martín, M. Grätzel, Adv. Mater. 2025, e05475.
Session FB-2 Concentrated Photovoltaics
FB-2:IL14 Ultra-high Solar Concentration for Ultra-efficient Photovoltaics: 1,000 Suns and Beyond
A. VOSSIER, PROMES-CNRS, Odeillo, France
Photovoltaic conversion under ultra-high solar flux (≥1000 suns) has long attracted attention for its potential to achieve record solar-to-electric efficiencies and reduce electricity costs by minimizing active cell area. Yet, despite its strong theoretical appeal, interest in ultra-high concentration photovoltaics (UH-CPV) has declined in recent years. This presentation revisits the physical motivations for developing PV cells operating under such extreme irradiance and analyzes the mechanisms that limit their performance in practice. After outlining the fundamental principles governing UH-CPV operation, we will review the dominant loss mechanisms—particularly resistive effects—that degrade efficiency at high flux, and discuss the strategies developed to mitigate them. Finally, we will present an overview of advanced solar cell architectures compatible with ultra-high concentration, highlighting how these conditions may enhance their operation and the remaining scientific and technological challenges to be addressed.
FB-2:IL15 Spectral Conversion of Sunlight for Boosting Plant Growth in Next Generation Greenhouses
A. TURSHATOV1, B.S. RICHARDS1,2, 1Institute of Microstructure Technology, Karlsruhe Institute of Technology, Germany; 2Light Technology Institute, Karlsruhe Institute of Technology, Germany
Greenhouses play a vital role in achieving global food security by enabling year-round crop production under controlled environmental conditions, even in harsh climates. As key components of the food–energy–water nexus, modern greenhouses integrate advanced technologies to optimize resource use and support the world’s growing population. Traditional greenhouses are typically made of either i) simpler plastic materials (a so-called polytunnel), or ii) metal frames with glass walls and ceilings (a classical glasshouse). There is a strong push in Europe towards “agrivoltaics” – installing photovoltaic panels in agricultural areas. Although this enables electricity generation, it typically does so at the expense of plant growth. This paper takes the opposite approach and seeks to boost crop even further, while seeking to generate electricity as a second priority. Specifically, it investigates how spectral conversion (luminescent) materials can improve photosynthesis by converting underutilized solar wavelengths, mainly in the ultraviolet and green regions, into those more efficiently absorbed within the photosynthetically active radiation (PAR) range. Finally, the possibility of achieving net zero energy consumption in the next generation of greenhouses will be briefly examined.
FB-2:L16 Spectral Splitting Low-gain Concentrator with Efficient Albedo Collection for Dual Junction 4-Terminals Configuration
F. MORABITO, CNR-IFN, Milano, Italy; M. PILIOUGINE, CNR-IMM Zona Industriale, Catania, Italy; D. FONTANI, P. SANSONI, CNR-INO, Firenze, Italy; C. GINESU, DFIS Politecnico di Milano, Milano, Italy; S.A. LOMBARDO, CNR-IMM, Catania, Italy; A. FARINA, S.M. PIETRALUNGA, CNR-IFN Milano, Italy
We designed, fabricated and tested a spectral-splitting low-gain optical concentrator for dual-junction 4-terminal photovoltaics. The core is a wedged optical right-angled prism, coupled to two complementary dichroic mirrors. A bifacial Si PV cell and a high-bandgap cell are separately used, respectively on the near-infrared and visible spectra. The design minimizes self-shading and land occupation. The tilt angle is counter-intuitive and lower than for standard bifacial installations, improving bifacial yield. Polar tracking is not mandatory. We numerically simulated performance in direct and diffuse light, also accounting for the backscattered irradiation from ground and by using licence-plate data for the optical glass, dichroic mirrors and PV cells. The Power Conversion Efficiency (PCE) has been estimated at different latitudes of installation, considering the excursion in elevation of the sun along the year and at different tilt angles. The device outperforms standard bifacial installations, up to 39% in annual PCE, and best performs at low latitudes. Indoor and outdoor tests on a first prototype indicate that PCE between 30% and 40% is expected for optimized optical coupling and azimuthal tracking, further leverageable by proper selection of the visible cell.
FB-2:L17 The Solar Tracking Revolution
A. MINUTO, E. CELI, G. TIMÒ, RSE, Piacenza, Italy
This paper introduces an innovative solar tracking philosophy, first developed for concentrator photovoltaic (CPV) and now adapted for flat-plate modules. The approach is based on a simplified, low-cost design that maintains high precision by integrating two key technologies: Shape Memory Alloy (SMA) actuators and a novel LED matrix sensor for real-time tracking control. Outdoor experiments demonstrated stable and accurate performance, achieving an absolute misalignment from solar rays below 0.1 mm in 90% of the operating time. Furthermore, accelerated lifetime testing confirmed the mechanical robustness of the SMA actuators, projecting an operational durability exceeding 30 years. These findings highlight the potential of this new solar tracker technology, representing an outstanding step toward higher-efficiency PV.
FB-2:IL18 Micro-CPV Device Architectures for Deep Space Solar Arrays
C. DOMÍNGUEZ, G. VALLEROTTO, A. BERMUDEZ-GARCIA, G. SIEFER, M. WIESENFARTH, A. GARCIA-SANCHEZ, S. ASKINS, I. ANTÓN, C. BAUR, P.L. COZ, Universidad Politécnica de Madrid, Madrid, Spain
The exploration of the icy moons of Jupyter and Saturn for signs of life is a strategic priority for the next large scientific mission of the European Space Agency, yet solar power generation for propulsion beyond Mars remains a critical challenge due to low-intensity, low-temperature (LILT) environments that may severely degrade the performance of multi-junction solar cells typically used in cover-interconnect-cell (CIC) arrays. This limits the achievable specific power of CIC panels under such conditions. Micro-concentrator photovoltaics (micro-CPV) offer a promising alternative by enhancing irradiance, operating temperature and radiation tolerance with compact architectures. This lecture presents the rationale, design, and preliminary demonstration of two micro-CPV device architectures tailored for deep-space missions: a silicone-on-glass Fresnel microlens array and a hybrid catadioptric system combining refraction and total internal reflection. Optical ray-tracing with realistic material properties guided their optimization. A first Fresnel prototype achieved 85% optical efficiency and ±5° angular tolerance, in close agreement with simulations. These architectures demonstrate pathways toward high-specific-power (>300 W/kg) solar arrays, supporting future deep space missions.
FB-2:IL19 Why is Hybrid CPV Technology a Good Way to Supply Electricity?
G. TIMÒ, A. MINUTO, E. CELI, Ricerca sul Sistema Energetico - RSE S.p.A, Piacenza, Italy
Concentrated Photovoltaics (CPV) underwent a long development phase, with installations increasing from 2005 and peaking significantly between 2011 and 2014, before experiencing a sudden decline between 2015 and 2016. Starting with the main reasons that hindered the success of CPV technology, this contribution presents new development perspectives that could renew interest in this technology. The focus is on CPV/PV hybrid modules with precise integrated solar tracking, combined with external low-resolution solar trackers which allow shifting tracking accuracy from the macroscopic to the mesoscopic level. This has, for the first time, decoupled the concentration factor from the external tracker’s precision. The use of shape memory alloy actuators instead of stepper motors has improved both the reliability and cost-effectiveness of solar tracking. The innovative design of CPV/PV hybrid modules makes them more appealing for building integration and agrivoltaic applications. Compared to traditional silicon photovoltaic systems based on single-axis trackers, the new CPV/PV hybrid technology has the potential to generate more energy while using up to a hundred times less semiconductor material, thereby reducing environmental impact, the lend use, and dependence on raw material supply.
Session FB-3 Concentrated Solar Thermal
FB-3:IL20 Design Strategies and Solar Aging of Selective Coatings in Concentrated Solar Thermal Systems
J.C. SÁNCHEZ-LÓPEZ, T.C. ROJAS, C.I. PARRA-MONTERO, M. SÁNCHEZ-PÉREZ, Instituto de Ciencia de Materiales de Sevilla (CSIC-US), Seville, Spain; R. ESCOBAR-GALINDO, Department of Applied Physics I, Escuela Politécnica Superior, Universidad de Sevilla, Sevilla, Spain; I. CAÑADAS, A. FERNÁNDEZ GARCÍA, CIEMAT-PSA, Tabernas, Almería, Spain
Enhancing the thermal stability of solar selective absorber (SSA) coatings is key to achieving efficient and durable concentrated solar power systems. Multilayer CrAlN-based absorbers deposited by HiPIMS have shown excellent optical selectivity (α ≈ 95%, ε ≈ 0.18) and stability up to 700 °C in ambient air, thanks to their intrinsic oxidation resistance and controlled synthesis using a simultaneous substrate bias. These optimized conditions extend the operational threshold by nearly 100 °C compared with current operation conditions (550 °C). However, intermetallic diffusion from metallic substrates still limits solar performance during prolonged exposure. To mitigate this, thin oxide barrier layers have been introduced between substrate and absorber, effectively reducing elemental interdiffusion and phase decomposition. XRD, TEM, and spectroscopic analyses confirmed the suppression of Cr₂N and CrNi intermetallic formation, while maintaining high absorptance (α ≈ 94-95%) after annealing at 800 °C. This combined strategy¬ (thermal diffusion barriers and CrAlN-based absorbers)¬ offers a promising route to extend the lifetime and efficiency of SSAs under realistic solar operation conditions.
FB-3:IL21 Design and Development of Multifunctional Ceramic Coatings for Concentrated Solar Thermal Receiver
T. NDIAYE1, R. REOYO-PRATS2, F. MERCIER3, R. BOICHOT3, E. BÊCHE1, T. ENCINAS3, S. COINDEAU3, L. CHARPENTIER1, 1PROMES-CNRS, Font-Romeu-Odeillo-Via, France; 2PROMES-CNRS, Perpignan, France; 3SIMaP-CNRS-UGA-Grenoble INP, Saint-Martin d’Hères, France
Solar receivers have to address several constraints when exposed to air at high temperature: resistance towards oxidation, maintenance of the solar absorptivity, limitation of the deformations and damages due to a succession of thermal cycling… Conventional materials (such as Inconel alloys) do not allow a working temperature beyond 600 °C due to severe oxidation rates at higher temperatures. A solution could be to coat a high temperature alloy with a ceramic coating. The alloy would be easy to machine and could support thermomechanical cycling. The coating would resist towards oxidation and maintain adequate solar absorptivity. This talk will present the 1D-model that was developed in order to estimate the repartition of stresses and strains along the depth of a multi-layered coated sample according to the layer thicknesses and to the properties of each component. Then we will present how thermal cycling is performed on ceramic-coated materials using the Solar Accelerated Ageing Facility (SAAF). Finally we will show how the treatments of X-Ray Diffractograms and optical profilometer can enable the estimation of the strains and stresses inside the materials. A good adequacy between the predictions and the experimental results has been evidenced.
FB-3:IL22 Thermo-optical Properties of Advanced High-temperature Solar Absorber Materials
T. ECHÁNIZ, I. GONZÁLEZ DE ARRIETA, J. GABIRONDO-LÓPEZ. M. SAINZ-MENCHON, R. FUENTE, G.A. LÓPEZ, Barrio Sarriena s/n, Leioa, Spain
The Group on Thermophysical Properties of Materials from the University of the Basque Country has studied the thermo-optical properties of CSP solar absorbers for over a decade. During this time, the Group has worked on developing a lab that can measure high-temperature directional spectral emissivity measurements (up to T=1000 °C and between 0 and 80°) in a controlled environment, room-temperature IR reflectance and UV-Vis-NIR bidirectional reflectance density function (BRDF) measurements, together with a complete microstructural characterization. In this contribution, we present experimental results corresponding to three different types of solar absorbing materials to be used in solar towers. First, we evaluate the optical response and microstructural stability of oxidized silicon coated stainless steel as a low-cost material. Second, we present results corresponding to ultrablack coatings, based on AZO-coated black spinel nanoneedles. Finally, we show a comparison of BRDF and spectral emissivity measurements performed in oxidized 3D-printed Inconel 718 samples for different periodic 1D patterns that enhance the solar absorption.
FB-3:IL23 Advanced Coating Solutions for the Development of Solar Thermal Materials
R. ESCOBAR-GALINDO1, J.C. SÁNCHEZ-LÓPEZ2, T.C. ROJAS2, M. KRAUSE3, 1Departamento de Física Aplicada I, Escuela Politécnica Superior, Universidad de Sevilla (US), Sevilla, Spain; 2Instituto de Ciencia de Materiales de Sevilla (CSIC-US), Seville, Spain; 3Helmholtz-Zentrum Dresden – Rossendorf, Dresden, Germany
Thermal conversion of solar energy into electricity is one of the most efficient methods of harnessing renewable energy. In this context, the development of new materials is crucial to improve the performance of Concentrating Solar Power (CSP) plants. Future thermal solar plants will require, among others, (i) mirrors with higher reflectivity, better protection and lower cost, (ii) absorber-receiver components operating at higher temperatures with wavelength-selective capabilities, or (iii) more stable materials in corrosive environments (e.g. molten salts). This presentation will give an overview on the use of surface engineering concepts such as tailoring multilayer materials and control of interface design, as applied to the aboved metioned key CSP components. In this presentation we will drawn specific examples from our own research. On the one hand, the design of metal-dielectric aperiodic multilayer solar mirrors using genetic algorithms and fabricated by physical vapour deposition (PVD) techniques will be shown to outperform state-of-the-art silver reflectors commonly used in CSP and photovoltaic systems. On the other hand, potential candidates for solar absorber/selective coatings with better thermal stability than commercial solutions (i.e. Pyromark) will be summarized.
FB-3:IL24 Optical Durability Testing of Materials for CST Components
A. FERNÁNDEZ-GARCÍA, R. SÁNCHEZ-MORENO, G. SAN VICENTE, I. CAÑADAS, A. MORALES, J. WETTE, N. BARANDICA, D. MOLINA, CIEMAT - Plataforma Solar de Almería, Tabernas, Almería, Spain; F. SUTTER, F. WIESINGER, L. CAMPOS, A.C. GONZÁLEZ-ALVES, German Aerospace Center DLR, Institute of Solar Research, Almería, Spain
Concentrated solar thermal (CST) energy is a key pillar in the transition towards a both sustainable and environmentally friendly new global energy model. CST shares the fundamental attributes of renewable sources, yet surpasses them in grid functionality. This energy offers the distinct advantages of dispatchability and flexibility, thanks to the integration of thermal energy storage systems. Additionally, it contributes to the stability and security of the power grid and plays a strategic role in industrial decarbonization. To ensure the reliable operation of CST plants throughout their entire service life, the materials used in the key components, such as reflectors and receivers, shall exhibit excellent optical properties that resist degradation over time. Developing durability assessment methods for these materials is crucial, as it enables both the comparison of different materials and the prediction of their useful lifetime under real operating conditions. These assessments are based on accelerated aging tests conducted in climate chambers, as well as on exposure to real outdoor conditions. This work presents a summary of the research activities carried out over the past two decades at CIEMAT-PSA in this field, by OPAC group, composed of researchers from CIEMAT and DLR.
FB-3:L25 Steelmaking Slags as Sustainable Absorber Materials in Concentrated Solar Thermal Plants
C. LINDEN, G. ALKAN, P. MECHNICH, F. FLUCHT, B. KÖLSCH, German Aerospace Center, Institute for Frontier Materials on Earth and in Space, Cologne, Germany; German Aerospace Center, Institute of Solar Research, Cologne, Germany
In times of climate change the transition to a sustainable yet competitive industry requires not only sustainable energy production but reliable and cost-effective energy storage (TES). Concentrated solar thermal (CST) -TES combines production and storage of solar energy by using absorber particles which absorb concentrated solar irradiation and store it in form of heat (≤ 1000 °C). Conventional absorber particles consist of bauxite proppants which are ecologically and economically demanding raw materials. Steelmaking slags offer a promising pathway to reduce primary resource mining while valorizing industrial by-products. In this study, five different slags (blast furnace slag, granulated slag, Eolit, Baselith, Lidonit) were assessed to evaluate the suitability of steelmaking slags as absorber particle material for CST-TES. The as-received powders were analyzed, granulated into particles and compared in regards to their mineralogy, thermo-mechanical properties, and solar absorptance. Initial investigations confirm slags to be promising candidates as absorber particles whereas Baselith, Eolit, Lidonit are especially promising due to their coloring. Their complex mineralogy provides suitable chemical composition and crystal quality for promising CST-related functional properties.
FB-3:IL26 Thermochemical Storage of Solar Heat via Redox Oxide Porous Ceramic Structures
C. AGRAFIOTIS, A. ELTAYEB, D. KOCH, M. PEIN, Institute of Future Fuels, German Aerospace Centre (DLR), Cologne, Germany; C. PAGKOURA, G. KARAGIANNAKIS, ARTEMIS Lab, Centre for Research & Technology Hellas (CERTH), Thermi, Thessaloniki, Greece; N. HORNSKOV, L. YUAN, J. MARCHER, Landson Advanced Ceramics A/S, Helsinge, Denmark
Heat from air-operated Concentrated Solar Power plants can be stored thermochemically by exploiting the enthalpy effects of reversible reduction-oxidation (redox) reactions of metal oxides: during on-sun operation solar-heated air is used to power the endothermic reduction of the oxide; the thermal energy can be entirely recovered by the reverse, exothermic, oxidation reaction during off-sun operation. Air is thus used both as heat transfer fluid and oxidant into direct contact with the storage oxide material. By employing porous ceramic monolithic structures like honeycombs and foams manufactured from such redox oxides, thermochemical heat storage can be directly hybridized with sensible one in the same storage volume. The concept development is presented holistically from high-throughput computational screening of redox oxide compositions to scalable synthesis of the shortlisted powders and then to their shaping to monolithic, robust ceramic honeycombs and foams. Finally, the proof-of-concept is demonstrated in modular thermochemical reactors/heat exchangers wherein the enthalpy of the oxidation reaction generates repeatable heat effects manifested as sensible temperature rise of both the porous structured solid and the air stream flowing through it upon cyclic redox operation.
FB-3:IL27 Excellent Solar Absorption and Storage Performance for Spinel/Olivine Ceramic Fabricated from Iron-rich Copper Slag
DONG ZHU, YAWEI LI, QINGHU WANG, State Key Laboratory of Advanced Refractories, Wuhan University of Science and Technology, Wuhan, China; Joint International Research Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan, China
Solid solar absorption/storage material is the crucial component for next-generation concentrating solar power (CSP) system, which could accelerate the global carbon neutrality. During the development of solid absorption/storage material, both high absorption/storage performance and low cost should be required for the practical application. Herein, iron-rich copper slag, as abundant and sustainable raw material, was used as the main raw material to develop novel solar absorption/storage ceramic. It is mainly composed of (MgxFe1-x)(FeyAl2-y)O4 spinel and (MgxFe2-x)SiO4 olivine, which were realized by introducing MgO/Al2O3 additives. This spinel/olivine composite ceramic achieved high solar absorption of 91.93%, due to impurity energy level absorption and lattice vibration absorption. Moreover, it realizes excellent storage property, including thermal storage density of 988.7 kJ/kg, thermal conductivity of 4.097 W/(m·K) and specific heat capacity of 1.014 J/(g·K). After service at 1000 °C for 100 h, it still retained structural integrity and stable absorption/storage parameters. Most importantly, this composite ceramic exhibits excellent mechanical performance, including high flexural strength (110.60 MPa), outstanding thermal shock resistance and wear performance. Thus, this study
FB-3:L28 Surface Modification of Absorber Particles by Dark Spinel and Steelmaking Slag-Based Coatings for Long-Term Solar Absorptance
G. ALKAN1, P. MECHNICH1, B. KÖLSCH2, 1German Aerospace Center (DLR) Institute of Frontier Materials on earth and in space, Köln, Germany; 2German Aerospace Center (DLR) Institute of Solar Research, Köln, Germany
The use of solid particles as direct heat absorbance and storage media promises enhanced storage densities in concentrated solar power (CSP) technologies. Ceramic based granular particles, like bauxite proppants or iron oxide particles, are state-of-the-art for particle receivers of concentrated solar power plants. Despite several beneficious properties such as high thermal shock resistance, sphericity, heat capacity, proppants exhibit a significant decrease in solar weighted absorptance after thermal exposure. The long-term optical performance of those particles, which are aimed to be operated over years, are crucial. In this study, we present a novel dry powder coating on ceramic absorber particles in a resonant acoustic mixer and subsequent sintering. A commercial deep-black Cu-Mn-oxide pigment and a sustainable alternative Fe-rich steelmaking slag were employed as coatings on ceramic particles. Using phase and microstructural analysis, the mechanism of the coating layer formation was discussed. The structural and optical measurements revealed the enhancement of the properties of ceramic absorber particles through this new modified coating process. Applicability of the dry coating process on different particle types was also examined with adjusted chemical composition and sintering time. What is more, the possibility of replacing black spinel pigments with secondary raw materials were discussed.
FB-3:IL29 Ceria and Iron Aluminate Active Materials for Solar Thermochemical Fuel Production
K. WARREN, Solar Energy Engineering Laboratory, Department of Mechanical and Process Engineering, ETH Zürich, Zürich, Switzerland
Widespread access to H2 and CO is critical for global decarbonization, yet producing a clean supply of these synthetic liquid fuel precursors at costs competitive with fossil-based alternatives remains constrained by the limited capacity and durability of incumbent electrolysis technologies. Thermochemical approaches that exploit the oxygen-exchange capacity of metal oxides offer a promising route to overcome these limitations, although challenges persist in identifying oxygen carriers capable of efficient operation within the confines of established chemical processes. In this presentation, benchmark candidates from two distinct classes of nonstoichiometric metal oxides - ceria fluorites and iron aluminate spinels - are examined for their effectiveness in facilitating thermochemical H2O and CO2 splitting. Their redox behavior, governed by oxygen- and cation-vacancy-mediated transport, respectively, is characterized through both closed- and open-system analyses to elucidate the relationship between thermodynamic properties and performance. The implications of these findings are discussed in the context of process integration, illustrating how the rational design of materials with tailored redox properties is poised to enable commercially viable routes to sustainable fuels.
FB-3:IL30 Thermochemical Processes for Fuels and Chemical Commodities
M. ROEB, German Aerospace Center (DLR), Institute of Future Fuels, Köln, Germany
Chemical energy carriers will play an essential role in the energy system of the future. The advantages of comparable power density and reliability to fossil fuels, as well as their versatile applications, make them an important component of the energy transition. Our research group is developing technologies that ensure the efficient production of chemical energy carriers and chemical commodities from renewable resources while allocating emphasis on the closure of the carbon-cycle. Thermochemical multistep processes are promising options, in particular related to the transport sector and to chemical industry. Such processes can be used to enhance the availability of solar energy in terms of potential energy related applications. One of the major barriers to technological success of many of those processes is the identification of suitable active materials like catalysts and redox materials with satisfactory durability, reactivity, and efficiency. One of the most striking challenges is to couple solar thermal energy to a chemical process while keeping it practical and reliable. The main challenges of those processes are being analyzed. Technical approaches and development progress in terms of solving them are addressed and evaluated with respect to their future potential.
FB-3:IL31 Elucidation of Reaction Mechanisms in Metal Nitrides for Renewable Ammonia Production
A. AMBROSINI, M.D. WITMAN, N.D. HUMPHREY, M. SHIVANNA, V. STAVILA, Sandia National Laboratories, Albuquerque, NM, USA; J.E. MILLER, I. ERMANOSKI, E.B. STECHEL, Arizona State University, Tempe, AZ, USA; D. TRINKLE, L.H. MIKEK, University of Illinois, Urbana-Champaign, IL, USA
The Solar Thermal Ammonia Production (STAP) process offers a renewable chemical looping pathway for ammonia (NH3) synthesis, operating at significantly lower pressures than the traditional Haber-Bosch method. This approach utilizes a family of metal nitride (MN) materials based on Co3Mo3N, and harnesses concentrated solar power as a sustainable heat source, replacing conventional hydrocarbons. By employing green sources of hydrogen (H2) and nitrogen (N2), the STAP process can markedly reduce the carbon footprint associated with ammonia production. In this process, the bulk MN serves as the nitrogen source, facilitating the diffusion of nitrogen atoms to the surface where they react with H2 to generate NH3. This reaction results in a nitrogen-depleted metal nitride that can be regenerated in-situ using N2, thus completing the cycle. Analysis of the solid-state chemistry of the metal nitrides is essential for elucidating the reaction mechanisms involved in NH3 synthesis and the subsequent re-nitridation process, resulting in the design of more efficient materials and novel compositions. Recent experimental and modeling efforts aimed at advancing this knowledge will be presented.
FB-3:IL32 Material Challenges for Advanced Concentration Applications
T. STEINBERG, School of Mechanical, Medical and Process Engineering, Faculty of Engineering, Queensland University of Technology, Brisbane, Queensland, Australia
Next generation Concentrating Solar Power (CSP) plants will operate at higher temperatures than current ones for improved efficiency and reduced cost to replace obsolete fossil fuel power plants. These advanced systems have three parts 1) solar receiver to capture energy in a fluid (liquid sodium), 2) extended-time thermal storage (sensible or latent salt) and 3) an advanced power block (supercritical CO2 (SCO2) Brayton cycle). Presented here, is a CSP plant utilizing Concentrating Solar Thermal technology operating at temperatures from 800 °C in the receiver where liquid sodium is used to capture the radiative energy, store the thermal energy in a thermal media (typically sensible or PCM salt) at 600-700 °C and operate a SCO2 power block operating > 600 °C. The work focusses on the selection and (experimental) validation of candidate materials as related to their degradation when exposed to such extreme conditions to allow the design and lifing to de-risk CSP allowing prototype systems to be evaluated. Initial work is done related to degradation of candidate materials exposed to these conditions and results are presented. Effects of material exposure at these conditions on mechanical strength degradation have also been initiated and are presented.
FB-3:IL33 Electro-Thermal Energy Storage (ETES) for Industrial Decarbonization: Magaldi’s Experience with the MGTES Fluidized Bed Thermal Battery
F. BASSETTI, C. BEVILACQUA, M. CILENTO, D. COPPOLA, L. MAGALDI, R. MAGALDI, Magaldi Power S.p.A, Roma, Italy
Thermal Energy Storage (TES) systems powered by renewables enable the delivery of dispatchable green heat at medium to high temperatures. Concentrating Solar Thermal (CST) with integrated TES offers reliable, clean thermal energy, enhancing efficiency and reducing dependence on fossil fuels. Magaldi has developed two patented TES technologies based on a fluidized bed of silica sand, selected for its thermal stability, durability and cost-effectiveness. The Magaldi STEM® is a CST TES system coupled with a beam-down solar concentrator, while the Magaldi Green Thermal Energy Storage (MGTES) is a Power-to-Heat (P2H) thermal battery, charged by renewable electricity and/or the grid. Both technologies integrate charging, storage and steam generation into a single fluidized bed module. Building on experience from the STEM® CST system in San Filippo del Mela (Italy) and the MGTES pilot “Alpha-4”, the first industrial MGTES system was commissioned in Q2 2025 at the Magaldi facility in Buccino (Italy). It features 7.5 MWh thermal capacity, 1.9 MWe charge power and generates steam at 200°C/11.5 bar. This work outlines the evolution of fluidized sand-bed TES from the first CST system to the MGTES P2H battery, marking a key step toward commercial deployment and industrial decarbonization.
FB-3:L34 High-Temperature Solar Cells for Concentrating Solar Systems
A. BELLUCCI1, E. BOLLI1, M. GIROLAMI1, M. MASTELLONE1, S. ORLANDO1, R. POLINI2, R. SALERNO1,2, A. SANTAGATA1, V. SERPENTE1, V. VALENTINI1, D.M. TRUCCHI1, 1Istituto di Struttura della Materia, National Research Council of Italy, Rome, Italy; 2Department of Science e Chemical Technologies, TorVergata University, Rome, Italy
Exploiting photons and heat is the key for innovation of solid-state converters to concentrating solar systems. High-temperature solar cells and solid-state thermal energy converters are rapidly maturing by applying hybrid thermionic-based mechanisms, such as thermionic-thermoelectric generation[1], thermionic-photovoltaic conversion [2, 3], and photon-enhanced thermionic emission (PETE) concept, which represent the most promisingly efficient (>50% efficiency) mechanism for the exploitation of concentrated sunlight. PETE converters rely on the concept that engineered semiconductor photocathodes can provide an efficient electron emission, obtained by a synergistic combination of photogeneration (i.e., photons) and thermionic emission (i.e., heat). High-temperature solar cells based on black diamond and nanodiamond-on-silicon cathodes are under development, as well as rugged-composition perovskites. Results of diamond-based converters under a high-flux solar simulator are reported by demonstrating for the first time the PETE conversion at temperatures from 300 to 600 °C [4] and by discussing future necessary advancements.
[1] DOI: 10.1002/aenm.201802310; [2] DOI: 10.1021/acsenergylett.0c00022; [3] DOI: DOI: 10.1002/aenm.202200357; [4] Trucchi et al., Joule, in print, 2025.