Metal halide perovskites are often viewed as electronically defect tolerant semiconductors. At the same time, their mixed ionic-electronic character and chemical reactivity can drive unexpected degradation pathways involving electrode materials. In particular, noble metals commonly employed as device contacts are not always chemically inert and can participate in electrochemical reactions that lead to metal transport through perovskite layers. In this talk, I will discuss how studies of gold migration in perovskite devices have led to a broader understanding of metal transport and doping in halide perovskites. I will describe how electrochemically generated noble-metal cations can form, migrate, and interact with the perovskite lattice, influencing both device stability and electronic properties. These findings suggest that metal transport should not be viewed solely as a degradation mechanism, but also as a potential route to dynamic doping and new device functionality. Finally, I will explore whether the electrochemical processes that limit long-term stability of perovskite optoelectronic devices be harnessed as useful functionality? Examples including dynamic doping and resistive switching suggest that the boundary between degradation and operation may be less distinct than traditionally assumed. Understanding this relationship may prove important both for realizing durable perovskite technologies and for developing new classes of adaptive electronic devices.

Over the past six years we have been studying the stability of mixed-halide perovskites. We used a series of advanced characterisation tools like intensity modulated photocurrent spectroscopy, hyperspectral photoluminescence, nano X-ray fluorescence, nano X-ray diffraction, X-ray photoemission electron microscopy and in-situ pair distribution function analysis.

By combining these complementary approaches, we have been able to follow degradation processes across multiple length scales and identify a major degradation pathway in mixed-halide perovskites. We outline three reasons why this degradation is particular harmful. In the end we will discuss how these insights reshape our understanding of halide segregation and how we can move towards stable mixed-halide perovskites. 

Perovskite solar cells (PSCs) have garnered significant attention in recent years due to their remarkable optoelectronic properties and the unprecedented performance gains achieved in an unprecedentedly short timeframe since their discovery. Among the various strategies to enhance PSC efficiency and stability, polymer additives have proven effective, either by incorporation into the perovskite bulk or by deposition on the surface via antisolvent engineering. Diketopyrrolopyrrole (DPP)-based conjugated polymers, widely studied in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs), represent a promising but underexplored class of additives for PSCs.
In this study, we developed stable n-i-p-based PSCs by introducing DPP-based polymers with biselenophene (poly-ADD1) and thienothiophene (poly-ADD2) donor units via antisolvent treatment. The resulting PSCs achieved PCEs of 21.0% (poly-ADD1) and 20.6% (poly-ADD2), both slightly surpassing that of the reference PSC (20.5%). More importantly, poly-ADD1 significantly enhanced thermal stability: after 1600 hours of thermal aging at 85ºC in ambient air, PSCs retained 67.0% of their initial PCE, compared with 29.0% and 27.0% for the reference and poly-ADD2 cells, respectively. Furthermore, under ambient storage conditions with exposure to oxygen and humidity, poly-ADD1-treated PSCs showed no measurable degradation over 1300 hours. In contrast, the reference cell retained only 79.0% of its initial efficiency, demonstrating the exceptional stability of treated cells. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) provides mechanistic insight, revealing that the selenophene-containing polymer poly-ADD1 forms a uniform and stable interfacial layer that effectively restricts Li⁺ migration and Au diffusion, suppresses AuI formation within the bulk, and thereby enhances long-term cell stability (under thermal and ambient stress); collectively, these findings underscore the potential of DPP-based polymers, particularly poly-ADD1, as universal interfacial modifiers that form conformal layers on perovskite surfaces, effectively mitigating Au and Li⁺ ion diffusion and enabling broadly applicable stability improvements in perovskite solar cells incorporating Au and Li-containing components.

All-perovskite multijunction solar cells promise to deliver power conversion efficiencies (PCEs) beyond the theoretical limit of single-junction devices at low fabrication costs. However, the sub-par performance of wide-bandgap perovskite subcells remains a key bottleneck limiting the efficiency gains of tandem architectures.

In this presentation, I will discuss how initial morphological and compositional disorder in as-deposited Br-rich, wide-bandgap perovskite films can be the primary cause of V_OC losses and stability issues in high-bandgap perovskite solar cells. I will then present our latest mitigation strategies based on templated growth of Br-rich perovskites, which improve halide homogeneity and suppress energetic losses, achieving open-circuit voltages approaching 90% of the theoretical limit across photovoltaic bandgaps ranging from 1.8 to 2.3 eV.

Building on these advances, we demonstrate efficient monolithic all-perovskite double-junction, triple-junction, and quadruple-junction solar cells with PCEs beyond 27% at a 1 cm² device area.

Metal halide perovskite solar cells have gained significant attention over the last decade due to their low-cost fabrication methods and high efficiency potential. Typically, perovskite films are prepared by solution-based deposition techniques, which offer short deposition times and a broad range of compositions.^[1] However, achieving conformal coverage of textured surfaces, highly relevant for monolithic perovskite/silicon tandem solar cells,^[2]or compositional gradients in the absorber material, to achieve graded Fermi levels,^[3] can be challenging with these techniques. These limitations can be overcome by co-evaporating the perovskite precursor materials.

Our work focuses on the vacuum-based preparation of perovskite absorbers with a band gap of about 1.68 eV, optimized for monolithic perovskite/silicon tandem solar cells. We show how the choice of hole-transporting material affects the composition of perovskite films in p-i-n solar cells.^[4] Our findings reveal that perovskites co-evaporated on spin-coated [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) contain a significantly smaller amount of FAI if the MeO-2PACz layer is washed with ethanol before the perovskite deposition. The reduced FAI content leads to a different morphology and alters the bromine to iodine ratio, impacting the solar cell performance and the band gap of the films.

We use two approaches, namely “seed layers”^[5] and “loaded hole transport layers”^[6], for tuning co-evaporated perovskite films through modifying the initial growth stage, yielding larger process windows, reduced sensitivity to substrate properties and improved process stability.

We study how the perovskite composition differs between planar and textured surfaces with random pyramids on silicon heterojunction bottom cells. Finally, fully textured perovskite/silicon tandem solar cells with ~30% PCE (certified) are demonstrated.

Our results illustrate multiple factors influencing the perovskite growth and highlight the potential of co-evaporation processes for the scalable preparation of perovskite/silicon tandem solar cells on textured substrates.

Despite rapid progress in small-area perovskite solar cells, translating high efficiencies into large-area monolithic modules remains a central challenge for commercial deployment. Here, we frame the cell-to-module gap as a property-distribution problem: a sub-centimetre cell statistically averages local variations in film quality, whereas a series-interconnected module is constrained by its least-performing sub-cell. Controlling spatial optoelectronic heterogeneity is therefore essential for scalable perovskite photovoltaics.

To address this bottleneck, we introduce a multi-functional crystallization-directing molecular additive into blade-coated perovskite precursor inks. The additive drives the formation of a large-grained, phase-pure absorber and improves optoelectronic uniformity across module-relevant areas. This strategy increases the active-area power-conversion efficiency from 22.0% to 23.0% for 0.125 cm² cells, from 19.0% to 21.3% for 3.9 cm² devices, from 17.8% to 21.2% for 15.5 cm² mini-modules, and from 13.7% to 19.0% for 100 cm² monolithic modules. Notably, the efficiency gain widens monotonically with area — from +1.0 percentage point in small cells to +5.3 percentage points in 100 cm² modules — reducing the absolute upscaling loss by a factor of 2.1.

The origin of this scale-dependent improvement is supported by multi-scale characterization. Large-area photoluminescence imaging reveals enhanced spatial uniformity, linking crystallization control to reduced property dispersion. Correlative scanning electron microscopy–cathodoluminescence shows a recrystallized large-grain population and suppressed secondary PbI₂ formation, and solid-state 2D ¹H–¹H spin-diffusion nuclear magnetic resonance confirms that the additive–perovskite lattice interaction is maintained across the relevant length scales.

Encapsulated mini-modules also show strong operational and environmental durability, retaining approximately 90% of their initial efficiency after 1000 h damp heat (85 °C, 85% relative humidity) and approximately 92% after 500 thermal cycles (−40 °C to 85 °C). Under outdoor open-circuit ageing in Nicosia, Cyprus, an encapsulated 4 cm² mini-module retained 85.2% of its initial efficiency over 159 days.

These results show that closing the cell-to-module gap requires controlling not only average film quality but also the spatial distribution of optoelectronic properties — a chemically tractable design principle for stable, manufacturable perovskite photovoltaics.

Vacuum-based deposition is a scalable, solvent-free industrial method ideal for uniform coatings on complex substrates. However, all-vacuum-deposited perovskite solar cells fabricated by thermal evaporation trail solution-processed counterparts in efficiency and stability due to film quality challenges, necessitating advancement and improved understanding. Here, we report a co-evaporation route for 1.67-eV wide-bandgap perovskites by introducing a PbCl2 co-source to optimize film quality. We promote perovskite formation with pronounced (100) ‘face-up’ orientation and deliver a certified all-vacuum-deposited solar cell with 18.35% efficiency (19.3% in the laboratory) for 0.25-cm2 devices (18.5% for 1-cm2 cells). These cells retain 80% of peak efficiency after 1,080 h under the ISOS-L-2 protocol. Leveraging operando hyperspectral imaging, we provide spatiotemporal spectral insight into halide segregation and trap-mediated recombination, correlating microscopic luminescence features with macroscopic device performance while distinguishing radiative from non-ideal recombination channels. We further demonstrate 27.2%-efficient 1-cm2 evaporated perovskite-on-silicon tandem cells and outdoor stability of all-vacuum-deposited tandems in Italy, retaining ~80% initial performance after eight months.

Metal halide perovskites have shown tremendous promise as absorber layers for next-generation photovoltaic devices benefiting from their intriguing photophysical behaviours. Given that their performance and stability are strongly influenced by the structural and electronic states established during film formation, it is imperative to develop a predictive understanding of how growth pathways and chemical environments determine these states. Such understanding is particularly important for vapour-deposited perovskites, which offer excellent prospects for scalable manufacturing but remain highly sensitive to interfacial and compositional perturbations.

In this talk, I will present our recent efforts to modulate the structural and electronic states of vapour-deposited perovskite semiconductors through interface and chemical engineering. First, I will discuss how buried templating layers direct crystallisation pathways and influence phase evolution during co-evaporation. By modifying the interfacial environment, we demonstrate controlled changes in crystal orientation, microstructure, and device performance, revealing the critical role of interfaces in determining the structural states that emerge during growth [1].

I will then show how impurities in formamidinium iodide influence perovskite formation through fundamentally different mechanisms depending on the deposition route. While impurities act as defect modifiers in solution-processed systems, they perturb stoichiometric evolution and crystallisation pathways in vapour-deposited perovskites, leading to distinct structural and electronic outcomes [2]. These results highlight the remarkable sensitivity of perovskite functionality to subtle chemical perturbations and provide new insight into the relationship between precursor purity, film formation, and long-term device stability.

Collectively, these studies reveal how interfaces and chemical composition govern the emergence of structural and electronic states in vapour-deposited perovskites. More broadly, they illustrate how controlling the emergence and evolution of structural and electronic states can provide new routes towards improved photovoltaic performance, enhanced operational stability, and scalable manufacturing of perovskite solar cells.

The commercialization of halide perovskites is heavily constrained by the toxicity of lead, particularly under strict European frameworks like the RoHS directive for consumer electronics and the Safe and Sustainable by Design (SSbD) framework, where lead triggers the H1 hazard criterion as a Substance of Very High Concern (SVHC). While replacing lead with alternative cations (e.g., Sn, Bi, Sb, Ge, Cs) is a major research driver, achieving true sustainability requires looking beyond power conversion efficiency (PCE) and simple material substitution. This work evaluates the holistic sustainability of lead-free perovskite devices by addressing critical chemical, methodological, and supply chain challenges:

• Toxicity and the SSbD Framework: While elements like Bi and Cs show lower acute toxicity than lead, recent toxicological research indicates that other essential precursors (e.g., SnI₂, FAI, MAI) and standard processing solvents like DMF (also flagged under the SSbD H1 criterion) pose significant hazards that must be mitigated through green solvent alternatives.
• LCA Methodological Gaps: Current Life Cycle Assessment (LCA) characterization factors (e.g., USEtox) lack comprehensive human toxicity metrics for emerging substitutes. This introduces severe risks when comparing lead-based and lead-free alternatives, demanding a rigorous update of LCA characterization factors aligned with recent toxicological data.
• Raw Material Criticality: The transition to lead-free alternatives shifts the burden toward materials like Sb, Bi, and Ge, which are listed as critical raw materials by the EU, alongside potentially critical elements like Cs.
• Circular Economy and Device Architecture: End-of-Life (EOL) management via low-energy recycling and remanufacturing is essential to prevent metal leaching and recover high-value critical materials.

Furthermore, as the absorber layer's direct environmental impact is often secondary to that of transparent conductive substrates (TCS) and noble metal electrodes, optimizing the whole device stack is key to scalability.

Ultimately, while improving PCE and operational lifespans remains paramount to lowering the cradle-to-grave environmental footprint, ensuring the market readiness of next-generation lead-free optoelectronics requires a parallel commitment to circularity, non-hazardous design, and robust sustainability metrics.

As metal halide perovskites approach technological maturity, the research is now shifting from record-breaking efficiencies toward stability, scalability, and environmental sustainability. While lead-based perovskites currently hold the highest performance in photovoltaics, lead-free alternatives are rapidly emerging, offering not only reduced toxicity but also distinctive optoelectronic properties. In this talk, I will present recent advances spanning from tin-based three-dimensional perovskites to bismuth halide-based compositions, highlighting how compositional and structural diversity can be exploited to target a broad range of optoelectronic applications. Particular attention will be devoted to the relationship between composition, defect physics, and stability. Tin-based perovskites enable narrower bandgaps suitable for infrared absorption and tandem applications, while low-dimensional bismuth-based compounds exhibit broadband visible emission arising from their localized electronic states. These features open new opportunities that extend beyond the capabilities of conventional lead-based materials. Beyond materials design, the talk will also emphasize the development of scalable and green processing strategies. I will discuss approaches ranging from mechanochemical synthesis of perovskite powders to the deposition of thin films via slot-die coating, demonstrating pathways toward industrially relevant fabrication while avoiding the use of toxic solvents. By integrating advances in materials chemistry with sustainable manufacturing, this talk reviews the development of stable, scalable, and environmentally friendly perovskite technologies.

Perovskite solar cells (PSCs) have attracted worldwide attention due to their high power conversion efficiency (PCE) and low-cost solution processing.

The development of chemically adsorbed monolayers that can efficiently collect photogenerated holes from the perovskite layer and transport them to a transparent conducting oxide (TCO) electrode as the hole-collecting layer (HCL) is a critical key to boosting the performance of p-i-n PSCs.

As the first generation of our multipodal hole-collecting monolayer materials, we developed a tripodal molecule composed of a triazatruxene core connected with three phosphonic acid anchoring groups (PATAT). We demonstrated that after being chemically adsorbed on the TCO surface, PATAT molecules tend to form a monolayer with a face-on orientation, resulting in improved hole-collection compared to their monopodal and edge-on oriented counterpart.

We also investigated the effect of the core structure and anchoring group on the properties of the corresponding monolayers as well as the performance of the devices.

Recently, we designed a series of isotriazatruxene derivatives bearing three phosphonic acid anchoring groups (iso-PATAT) and its halogen-substituted derivatives. Isotriazatruxene has two indole moieties facing each other, leading to a steric hindrance when bulky substituents such as alkyl phosphonic acid groups were introduced into –NH positions. After being chemically adsorbed, instead of binding to the TCO surface, some phosphonic acid groups were found to point upward, leading to a hydrophilic and face-on oriented monolayer. P-i-n PSC devices using these iso-PATAT molecules as hole-collecting monolayers were fabricated and evaluated. The single-junction and monolithic all-perovskite tandem solar cells fabricated with iso-PATAT derivatives showed a champion efficiency approaching 26 and 29%, respectively.

In this presentation, our design for multipodal molecules, characterization, and device evaluation will be introduced in detail.

Tin-based perovskite solar cells have emerged as attractive lead-free alternatives to their lead-based counterparts due to their suitable optoelectronic properties and lower environmental impact. However, their development is still limited by the easy oxidation of Sn²⁺, high defect densities, severe non-radiative recombination, and poor operational stability[1], [2], [3].

In this work, sulfur-containing molecular additives are employed to improve the performance and stability of FASnI₃ perovskite solar cells. The interaction between sulfur functional groups and tin species modulates the crystallization process, suppresses defect formation, and reduces trap-assisted recombination. As a result, improved film morphology, enhanced charge-carrier dynamics, and lower non-radiative losses are achieved.

In addition to bulk defect passivation, the incorporation of sulfur-based molecules influences the energetic landscape at the perovskite interfaces, promoting more favorable energy-level alignment and more efficient charge extraction while suppressing interfacial recombination losses. These effects translate into improved photovoltaic performance and enhanced operational stability under continuous device operation.

This study demonstrates that sulfur-mediated molecular engineering represents an effective strategy to simultaneously control defects, reduce recombination losses, and optimize interfacial energetics in tin-based perovskites, providing new opportunities for the development of stable and environmentally benign lead-free perovskite solar cells.

Understanding the α-phase stability of FACsPbI₃ in halide perovskite/MXene heterojunctions for Carbon based perovskite solar cells

Zait Ayala^a,b, Ramses Miranda^a, Juan Dávalos^c and Monica Lira*^a

1. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and the Barcelona Institute of Science and Technology (BIST), Building ICN2, Campus UAB, E-08193 Bellaterra, 08193, Barcelona, Spain.
2. Universidad Nacional de Ingeniería (UNI).
3. Instituto de Química-Física “Blas Cabrera”, CSIC, Serrano 119, 28006 Madrid, Spain.

Corresponding autor: monica.lira@icn2.cat

Formamidinium–cesium lead iodide (FACsPbI₃) perovskite solar cells (PSCs) are promising candidates for next-generation photovoltaics owing to their near-optimal bandgap (~1.56 eV), excellent optoelectronic properties, and reduced susceptibility to halide segregation. However, residual lattice strain and interfacial defects accelerate the transformation of the photoactive α-phase into the non-photoactive δ-phase under ambient conditions, thereby limiting long-term operational stability.

In this work, we fabricate carbon-based FACsPbI₃ PSCs entirely under ambient atmosphere (19–21 °C, 50–60% RH) by incorporating a 2D Ti₃C₂Tₓ MXene–PEAI hybrid interlayer between the perovskite absorber and the hole transport layer. Delaminated Ti₃C₂Tₓ MXene was prepared via TPAOH-assisted intercalation and subsequently functionalized with phenethylammonium iodide (PEAI) to simultaneously passivate interfacial defects, relieve residual strain, and stabilize the α-phase of FACsPbI₃.

Fourier-transform infrared (FTIR) spectroscopy confirms the interaction between PEAI and MXene through a red shift of the N–H stretching vibration. X-ray diffraction (XRD) verifies the formation of phase-pure α-FACsPbI₃ with enhanced crystallinity following thermal optimization, while scanning electron microscopy (SEM) reveals enlarged grains resulting from MACl-assisted crystallization. UV–Vis spectroscopy shows that the optical bandgap remains unchanged at 1.56 eV. Our results demonstrate that the engineered halide perovskite/MXene:PEAI interface markedly improves charge-carrier dynamics. Time-resolved photoluminescence (TRPL) measurements show an increase in the average carrier lifetime from 19.88 ns for the control device to 103 ns after PEAI treatment. Electrochemical impedance spectroscopy (EIS) further reveals increased recombination resistance, indicating more effective defect passivation and suppressed non-radiative recombination. In addition, incident photon-to-current efficiency (IPCE) measurements demonstrate enhanced charge-collection efficiency. Carbon-electrode devices achieved power conversion efficiencies (PCEs) of up to 17%, while reference Au-electrode devices incorporating the MXene:PEAI interlayer exceeded 20%. Overall, this interfacial engineering strategy provides a promising route toward scalable, low-cost, and highly stable perovskite solar cells fabricated entirely in air.

Inverted p-i-n perovskite solar cells (PSCs) have emerged as highly promising architectures since their inception [1]. However, obtaining highly reproducible and uniform perovskite films over hydrophobic self-assembled monolayers (SAMs) remains a critical bottleneck [2]. While molecular design strategies like amorphous self-assembled multilayers have been proposed to mitigate interfacial degradation [3], scalable alternatives to conventional anti-solvent quenching are urgently required. This work introduces an optimized Flexible Infrared-Assisted (FIRA) crystallization methodology combined with a sol-gel derived NiOx / Cascade SAM hole transport layer (HTL) [4]. To address the severe dewetting of the perovskite solution, we utilize a sequential hybrid SAM configuration (MeO-2PACz/V-1779) in conjunction with 1,6-hexylenediphosphonic acid (6dPA) to achieve dual-site interfacial passivation and enhanced surface wettability [5, 6]. Our investigations reveal that the duration of the vacuum pre-step is a key parameter regulating crystallization kinetics [7]. Precise tuning of the sol-gel chemistry and metal oxide interfaces [8, 9] enables the optimization of carrier transport. Specifically, increasing the vacuum pre-step from 40 to 60 seconds dramatically suppresses the photoinactive yellow delta-phase network at the grain boundaries from 7.3% to 2.5%, as quantified by Optical Microscopy (OM) morphology analysis. This suppression eliminates shunt pathways and reduces the dark leakage current, which is critical for both photovoltaic and photodetector performances [10]. Consequently, the optimized FIRA-PSC achieved a champion power conversion efficiency (PCE) of 17.1% (Voc = 1.07 V, FF = 67%) on a diluted NiOx stack, showcasing a viable pathway for high-throughput, solvent-green manufacture of highly stable perovskite optoelectronics.