Halide perovskites quickly overrun research activities in new materials for cost-effective and high-efficiency photovoltaic technologies.  Since the first demonstration from Kojima and co-workers in 2007 [1], several perovskite-based solar cells have been reported and certified with rapidly improving power conversion efficiency, now approaching the theoretical limit.  Recent reports demonstrated that perovskites outperform the most efficient photovoltaic materials to date. At the same time, they still allow solution processing as a potential advantage in delivering a cost-effective solar technology.

The most stable and efficient perovskites contain lead. Lead (Pb) is one of the most toxic elements and has been used by humans for thousands of years. With only a few exceptions, each widespread application of lead has been banned systematically due to dramatic environmental and health consequences. However, we are now at the dawn of the perovskite era, potentially requiring yet again the widespread application of lead [2].

Lead-free alternatives have been reported with impressive progress in power conversion efficiency for tin-based (lead-free) perovskites. However, the stability of tin-based perovskite solar cells is still unexplored. In the present talk, we will focus on the stability of tin-based (lead-free) perovskite solar cells.

Halide perovskite solar cells have revolutionized the photovoltaic field in the last decade. In a decade of intensive research it has been a huge improvement in the performance of these devices. However, the two main drawbacks of this system, the use of hazardous Pb and the long term stability, still to be open questions that have not been fully addressed. The photoconversion performance of perovskite solar cells containing alternative metals to Pb is significantly lower than the reported for devices containing Pb, where Sn-based perovskite solar cells is the alternative reporting higher photovoltaic performance close to 15%. Nevertheless, Sn-based perovskite solar cells exhibit a long term stability lower than their Pb containing counterparts, making stability their main problem. In this talk, we highlight how the use of proper additives can increase significantly the stability of formamidinium tin iodide (FASnI3) solar cells and lasers as well as PEA2SnI4 red emitting LEDs. We also discuss about the different mechanism affecting the stability of these devices, beyond the oxidation of Sn2+, and how they can be countered. In one line summary, we show that proper additives can play an important role in stabilization of Sn-based optoelectronic devices as solar cells, LEDs and lasers.

Halide perovskites have captivated the research community over the past decade mainly in the photovoltaic field as a new generation of absorber materials for high-efficiency and low-cost solar cells. Nowadays, the power conversion efficiency (PCE) is reaching 25.7% for single cells and 31.3% for Perovskite/Si tandem cells. Moreover, halide perovskites exhibit attractive potential for Lasers, LEDs, Photodetectors, Photocatalysis. Nevertheless, despite promising low manufacturing costs, short payback time and abundant material resources, the potential industrial use of halide perovskites is still be hampered by toxicity issues, device stability and upscaling. Researchers are also looking for alternative materials related to the substitution of Pb by Sn in standard halide perovskite structures [1,2], double perovskite structures, perovskite-like structures or even non-perovskite structures such as rudorfittes. Importantly, the low-bandgap Pb-Sn alloyed perovskite allows the building of all-perovskite tandem solar cells that shall overcome the performances of single-junction perovskite cells [3,4]. In fact, of all possible means to improve perovskite film quality and suppress nonradiative recombination in optoelectronic devices for a high photo conversion efficiency purpose, the surface and interface functionalizations after the assembly with charge transport layer (CTL) are one of the most critical parameters [5,6]. In view of the sophisticated chemical and physical properties of Sn-based perovskites, theoretical calculations based on density functional theory (DFT) may provide a useful insight into the interplay between absorbers and CTLs. Here, FASnI3 is chosen as a benchmark material. We thoroughly investigate the influence of its surface termination on structural and electronic properties when interfacing with organic C60 (100) and inorganic SnO2 (100) and (110), including the intermediate work function calculations on the free-standing slabs. Based on the theoretical methology developed in our team [7], we have evidenced the proportionality between work function shifts and surface dipoles, providing an additional microscopic insight into interfacial properties in lead-free heterostructures.

Perovskite solar cells (PSCs) have created much excitement in the past years and attract spotlight attention. This talk will provide an overview of the reasons for this development highlighting the historic development as well as the specific material properties that make perovskites so attractive for the research community.[1-3]

The current challenges are exemplified using a high-performance model system for PSCs (multication Rb, Cs, methylammonium (MA), formamidinium (FA) perovskites).[2,3] The triple cation (Cs, MA, FA) achieves high performances due to suppressed phase impurities. This results in more robust materials enabling breakthrough reproducibility.

Through multication engineering, usually not-considered alakali metals, such as Rb, can be studied[5] resulting in one of the highest voltages compared to the bandgap. Polymer-coated cells maintained 95% of their initial performance at elevated temperature for 500 hours under working conditions, a crucial step towards industrialisation of PSCs.

To explore the theme of multicomponent perovskites further, molecular cations were re-evaluated using a globularity factor. With this, we calculated that ethylammonium (EA) has been misclassified as too large. Using the multication strategy, we studied an EA-containing compound that yielded a high open-circuit voltage of 1.59 V. Moreover, using EA, we demonstrate a continuous fine-tuning for perovskites in the "green gap" which is relevant for lasers and display technology. [6]

The last part elaborates on a roadmap on how to extend the multication to multicomponent engineering providing a series of new compounds that are highly relevant candidates for the coming years, also in areas beyond photovoltaics, for example for medical scintillation detectors.[6,7]

[1] N. Jeon et al., Nature (2015)

[2] J. Lee et al., Advanced Energy Materials (2015)

[3] D. McMeekin et al., Science (2016)

[4] M. Saliba et al., Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency, Energy & Environmental Science (2016)

[5] M. Saliba et al., Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance, Science (2016).

[6] S. Gholipour et al., Globularity-Selected Large Molecules for a New Generation of Multication Perovskites, Advanced Materials (2017)

[7] S. Turren-Cruz, A. Hagfeldt, M. Saliba, Methylammonium-free, high-performance and stable perovskite solar cells on a planar architecture, Science (2018)

[8] V. Mykhaylyk, H. Kraus, M. Saliba, Bright and fast scintillation of organolead perovskite MAPbBr3 at low temperatures, Materials Horizons (2020)

Colloidal lead halide perovskite (LHP) nanocrystals (NCs), with bright and spectrally narrow photoluminescence (PL) tunable over the entire visible spectral range, are of immense interest as classical and quantum light sources. Severe challenges LHP NCs form by sub-second fast and hence hard-to-control ionic metathesis reactions, which severely limits the access to size-uniform and shape-regular NCs in the sub-10 nm range. We show that a synthesis path comprising an intricate equilibrium between the precursor (TOPO-PbBr₂ complex) and the [PbBr₃^-] solute for the NC nucleation may circumvent this challenge [1]. This results in a scalable, room-temperature synthesis of monodisperse and isolable CsPbBr₃ NCs, size-tunable in the 3-13 nm range. The kinetics of both nucleation and therefrom temporally separated growth are drastically slowed, resulting in total reaction times of up to 30 minutes. The methodology is then extended to FAPbBr₃ (FA = formamidinium) and MAPbBr₃ (MA = methylammonium), allowing for thorough experimental comparison and modeling of their physical properties under intermediate quantum confinement. In particular, NCs of all these compositions exhibit up to four excitonic transitions in their linear absorption spectra, and we demonstrate that the size-dependent confinement energy for all transitions is independent of the A-site cation.

   We then show that this synthesis – relying on the labile ligand capping with TOPO-phosphinic acid mixture – makes for a convenient platform for the subsequent surface functionalization with diverse capping ligands [2]. Robust surface functionalization of highly ionic surfaces, as is the case of LHP NCs, has remained a formidable challenge due to the inherently non-covalent weak surface bonding. Leveraging the vast and facile molecular engineering of phospholipids, we present their efficacy as surface capping ligands for LHP NCs. Molecular dynamics simulations and solid-state NMR confirm that the surface affinity of these zwitterionic molecules is primarily governed by the geometric fitness of their anionic and cationic moieties. Judicious selection of the ligands yielded colloidally robust FAPbBr₃ and MAPbBr₃ NCs and enabled colloids in a variety of solvents, from n-hexane to acetone. Robustness of the surface capping is also reflected in optical properties: NCs exhibit PL quantum yield (QY) above 96% after numerous purifications. NCs are essentially blinking-free at a single particle level.

Metal halide perovskite solar cells have achieved record efficiencies of over 25%, comparable to mainstream silicon solar cells. However, the processing method and operational stability need further development to bring this technology to commercialization. In this context, we use a flash-infrared annealing method, which is environmentally friendly and rapid processing, without the use of toxic chlorobenzene, to process highly stable perovskite solar cells. Therefore, this work reveals the phase stabilization mechanism for perovskite halide films through thermodynamic, structural, and photophysical analysis related to process parameters optimization.[1] Measuring the enthalpy changes of the FAPbI3 composition at different heating rates allows us to calculate an activation energy of 1.8 eV for the black perovskite phase transition. We explore different heating regimes for triggering the phase transformation and analyze the evolution of the microstructure with an empirical calculation of the average crystal growth velocity required to form a compact film on the micron and submicron scales. A key interplay between perovskite halide thin-film crystallization phenomena and manufacturing aspects will be addressed.[2]

The increasing interest in lead-free photovoltaics has accelerated research efforts  worldwide, in particular, tin has been recognized as one of the most promising alternatives, exhibiting suitable optoelectronic properties, potentially decreased toxicity, and device performance. Nonetheless, the development of tin-based perovskites has been primarily hindered because of the ease of oxidation from Sn2+ into Sn4+, which promotes degradation mechanisms and compromises the long-term stability.

Besides this intrinsic challenge, most studies have focused on spin coating as the main deposition method for the absorber layer, which is not compatible with large area manufacturing techniques like roll-to-roll or sheet-to-sheet production. In this work, we explore blade coating and inkjet printing as versatile processes well-suited for commercial production; ink engineering of the solvent system and additives was used as a strategy to control the crystallization dynamics and obtain pinhole-free films on flexible substrates. Furthermore, the influence of processing conditions such as the coating speed, drying method, and waveform design on the perovskite morphology was analyzed. The potential industrial applicability of completed devices was tested through stability characterization after lamination and large area module fabrication.

In this talk, we explore the origin of preferred doping levels in perovskite solar cells (PSCs), using drift-diffusion simulations, and present some experimental techniques for obtaining them in real devices. We show how, in general, n-i-p devices will tend to perform better with a p-doped perovskite, whereas in p-i-n devices an n-type perovskite is preferred. Based on this, certain methods, techniques and compositions may fundamentally limit the maximum achievable PCE for certain device configurations. For example, while originally high-performance perovskite-based tandem cells were made using a regular n-i-p configuration, they are now predominantly made using an inverted p-i-n structure meaning that the corresponding changes should be made to the perovskite absorber layer. Our findings also have implications for materials which have a tendency to self-doped, such as tin-based perovskites. The origin of the preferred doping levels is due to the high absorption coefficients and relatively short diffusion lengths of halide perovskites which can impede effective charge extraction at the front and back contacts. While we show that the location of the preferred doping level in PSCs is generically a function of device architecture in most real PSC devices, the carrier mobilities (which are a function of deposition conditions) also play an important role and can exasperate or counteract any problematic charge extraction due to the localisation, and transportation, of the photogenerated carriers.

Hybrid tin (Sn) perovskite has been regarded as the most promising alternative material for lead (Pb) based perovskite, achieving a PCE of over 14% in 2021.[1] Antisolvents treatment has been widely used in the preparation of different Sn perovskite to improve the film quality and device performances.[2]  However, the mechanism behind the antisolvent treatment for Sn perovskite is still unclear.

In this work we studied the effects of different antisolvents on 2D/3D Sn perovskite (PEA_0.2FA_0.8SnI₃) perovskite solar cells. Diisopropyl ether (DIE), Diethyl ether (DE) toluene and chlorobenzene (CB) are applied as antisolvent during the film fabrication. Among these antisolvents the perovskite film treated by DIE revealed the highest crystallinity, achieving a PCE of 10.2%, better than DE, toluene and CB sequentially. We found that the origin of the improvement of PCE treated by DIE is correlated to the better distribution and higher fractions of the 2D phase inside the film, leading to better film quality and higher open circuit voltage. Besides, the higher amount of 2D phase can also enhance the stability of Sn perovskite under ambient atmosphere. Our findings not only show the importance of the 2D phase in 2D/3D Sn perovskite but also suggest that the compositions of the mixed cation perovskite could be influenced by different antisolvents.

The consequences of ionic migration represent one of the major bottlenecks in the achievement of real large-scale and stable commercial perovskite solar cells. These consequences include slow kinetic phenomena such as hysteretic responses, coupled with light-induced accumulation capacitance and negative capacitance, directly affecting photovoltage values.¹ As dopants in the bulk or at the interfaces, alkali metals have proven to be good allies in the race to mitigate the perovskite ionic migration or its effects.² However, the exact role of the alkali in each case still need to be clarified. In this work, we have use Li, Na and K as doping agents at the ESL/PVK interface. We have found that the beneficial effects lie in a modulation of the migrating ions depending on the ionic size of the alkali dopant. The analysis through impedance spectroscopy and time-resolved photoluminescence, among others, clarify the reasons behind an outstanding photovoltage up to 1.65 V achieved for pure MAPbBr₃ PSCs.

The power conversion efficiency (~15%) of Sn-based PSCs (Sn-PSCs) has so far lagged behind that of Pb-based PSCs (25.7%). The Achilles heel of Sn perovskites has been the spontaneous oxidation of Sn²⁺ to Sn⁴⁺, which leads to charge trapping and background hole doping [1]. Pioneering work in the field has shown that sublimation, additive treatments, and functionalization with 2D materials can mitigate Sn(II) to Sn(IV) oxidation. 

Photoluminescence (PL) spectroscopy is a powerful tool for understanding photovoltaic materials as the photoluminescence quantum yield (PLQY) is correlated with the non-radiative voltage loss (and thus PCE). While bulk PL has been used to great effect in the field so far, it is limited in that it averages all of the ensemble PL processes occurring throughout the film. PL microscopy on the other hand provides the opportunity to study the microscopic heterogeneity that leads to voltage loss in semiconductors. Indeed, landmark studies have linked microstructural heterogeneity with voltage loss in MAPbI₃ [2] and wide-bandgap perovskite compositions relevant to tandem applications [3-5]. This insight has helped inform surface passivation strategies that have pushed the V_OC in Pb-based PSCs to unprecedented heights. Remarkably, there are few reports that tackle the issue of microscale heterogeneity in Pb-free PSCs.

In this study, we use a unique microscopy toolkit based on scanning probe microscopy, hyperspectral PL imaging and PL lifetime mapping to establish structure-function relationships between PEA_0.2FA_0.8SnI₄ heterogeneity and device performance. We find (i) strong correlation between local conductance and local photoluminescence; (ii) photoluminescence homogeneity improves with SnF₂ treatment, leading to improvements in device PCE; (iii) the photoluminescence intensity of the 3D phases is correlated with their proximity to the 2D (n = 1, n = 2) phases. We expect findings from multi-modal microscopy studies such as this one to inform the further progression of Sn-based PSCs towards >20% efficiency.

[1] Lanzetta, L.; Webb, T.; Zibouche, N; X. Liang, X.; Ding, D.; Min, G.; Westbrook, R. J. E.; Gaggio, B.; Macdonald, T. J.; Islam, M. S.; Haque, S. A. Nat. Commun., 2021, 12, 2021

[2] deQuilettes, D. W.; Vorpahl S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.;, Snaith, H. J.; Ginger, D. S. Science, 2015, 348, 683

[3] Macpherson, S.; Doherty, T. A. S.; Winchester, A. J.; Kosar, S.; Johnstone, D. N.; Chiang, Y. -H.; Galkowski, K.; Anaya, M.; Frohna, K.; Iqbal, A. N.; Nagane, S.; Roose, B.; Andaji-Garmaroudi, Z.; Orr, K. W. P.; Parker, J. E.; Midgley, P. A.; Dani, K. M.; Stranks, S. D. Nature, 2022, 607, 294

[4] Frohna, K.; Anaya, M.; Macpherson, S.; Sung, J.; Doherty, T. A. S.; Chiang, Y. -H.; Winchester, A. J.; Orr, K. W. P.; Parker, J. E.; Quinn, P. D.; Dani, K. M.; Rao, A.; Stranks, S. D. Nature Nanotechnol., 2022, 17, 190

[5] Taddei, M.; Smith, J. A.; Gallant, B. M.; Zhou, S., Westbrook, R. J. E; Shi, Y.; Wang, J.; Drysdale, J. N.; McCarthy, D. P.; Barlow, S. R.; Snaith, H. J.; Ginger, D. S., ACS Energy Letters, 2022, 7, 4265

Metal Halide Perovskite (MHP) semiconductors have emerged as very promising materials for photovoltaics, light-emitting diodes (LEDs) and other optoelectronic applications. Despite the outstanding performance levels that have been reported for MHP-based devices in the last years, which in many cases roughly graze the maximum theoretical efficiency limits, there is still a long way to go until reaching a complete understanding of the working principles and photo-electrochemical mechanisms involved in the charge carrier generation/recombination dynamics. Particularly problematic for the settlement of this technology towards market applications is the widely reported limited long-term stability of the devices. The strong ionic character of MHPs, as well as the ion mobility/migration and the gradual formation of crystalline defects upon exposing to light and/or to an external electric field, are factors that detrimentally contribute to achieve acceptable stability levels and aggravate the complexity behind the functioning of MHP-based devices. Upon careful optimization, we have prepared high-purity CsPbBr₃ nanocrystals (NCs) and fabricated high-performing green light-emitting LEDs with luminance and efficiency values beyond 80000 Cd·m^-2 and 20%, respectively. I will discuss about our recent results obtained upon the advanced characterization of the LEDs, through a series of steady-state and frequency-resolved techniques, that will unambiguously contribute to a deeper understanding of this exciting but intricate lighting technology. The identification of interfacial and bulk phenomena, as well as the impact of temperature and other relevant parameters on the light-generation, ion rearrangement and long-term stability of devices will be discussed in detail.

Currently, two-dimensional tin-based halide perovskites (2D- THP) have drawn attention owing to improved ambiental stability, low toxicity, thickness dependant optical properties, and high exciton energy binding [1, 2], showing great potential to be exploited as lead-free visible light emitters on optoelectronic and photovoltaic devices [3]. Moreover, optical properties and carrier mobility can be adjusted as a function of organic cations length, opening a full gamut of possibilities for the design and development of new Ruddlesden Popper perovskite nanostructures [4]. Among 2D- THPs reported now, TEA₂SnI₄ perovskite has shown some interest in LED applications because of its high exciton energy binding (calculated in 51.1 meV) and low exciton- phonon interactions [5]. In the literature, 2D- TEA₂SnI₄ has been prepared by LARP and anti-solvent approaches, showing a PLQY record of 18.85% and 23 % on nanodisks solution [6,7] and thin film [8] respectively. Although, the development of nano- and microcrystals have not been completed and explored for this material because of uncontrollable crystallization rate, the formation of native defects, and poor passivated surfaces [9]. Moreover, the synthesis and physical properties of TEA₂SnBr₄ and TEA₂SnCl₄ nanomaterials have not been reported yet. For the first time, TEA₂SnX₄ (X= Cl, Br, I) micro and nanocrystals were synthesized by the hot injection method. We determine that the size and physical properties of TEA₂SnX₄ micro and nanocrystals are determined by parameters such as temperature and molar ratio of precursors. For the case of TEA₂SnCl₄ and TEA₂SnBr₄, we observe a broad PL band emission centered at 595 nm and 608 nm respectively. In both cases, we recorded a high Stokes shift (approximately 300 nm), and hence, it might be indicative of self-trapped excitons recombination mechanisms. The maximum PLQY measured in these samples was 50 % for TEA₂SnBr₄, 20 % for TEA₂SnCl₄, and 3% for TEA₂SnI₄. For TEA₂SnI₄ micro and nanocrystals, optical properties are a bit similar to the reported in the literature [6,7], represented by a sharp band emission centered at 647 nm with an FWHM = 38 nm at 300 K. PL and TRPL measurements were conducted at different temperatures to understand the optical properties of TEA₂SnX₄ micro and nanocrystals. In all cases, we observe an X-ray diffraction pattern characterized by strong reflections which is consistent with the quantum well like the structure of 2D hybrid tin halide perovskites . Additionally, ¹H,¹³C and ¹¹⁹Sn nuclear magnetic resonance, Raman spectroscopy, X- ray photoelectron spectroscopy and transmision electron microscopy measurements were carried out.

Lead halide perovskites successfully advance towards applications in solar cells, light-emitting devices, and high-energy radiation detectors. Recent progress in understanding their uniqueness highlights the role of optoelectronic tolerance to intrinsic defects, particularly long diffusion lengths of carriers, and highly dynamic 3d inorganic framework. This picture indicates that finding an analogous material among non-group-14 metal halides can be very challenging, if possible at all. On the other hand, Sn (II) iodide perovskites exhibit comparably good performance in photovoltaics when synthesized with a low number of trap states. The main challenge with this material originates from the easiness of the trap states generation, which are typically ascribed to the oxidation of Sn(II) to Sn(IV). In this work, we describe the synthesis of colloidal monodisperse FASnI₃ NCs, wherein thorough care on the purity of precursors and redox chemistry reduces the concentration of Sn(IV) to an insignificant level, to probe the intrinsic structural and optical properties of these NCs.

The evolution of metal halide perovskites in the last decade has originated a new family of materials for optoelectronic applications with unprecedented properties. However, the great performance values achieved, particularly in the field of photovoltaics, are usually based on lead-based perovskites and environmentally aggressive synthetic methods. It is thus essential to explore new avenues that take advantage of the best properties of metal halide perovskites with more sustainable methods. As an approach to achieve this objective, we analyze the rich variety of this family of materials, focusing on the differential properties of multiscale structures. Perovskite macro and nanocrystals can provide crucial tools to tackle the current environmental challenges that hinder their tangible impact on the final applications. We present new synthesis and passivation methods to fabricate device-oriented perovskite monocrystals in the macro and nanoscale, studying the physical processes controlling the luminescence as well as charge transport and recombination dynamics.

The expanding market of photonic devices is ever-growing with a global size of 772 B$ (2021), which is well above the semiconductor market (555 B$ in 2021). LEDs and lighting, displays, telecom, sensors, and photovoltaics are the prominent applications. Nowadays, conventional optoelectronic device manufacturing requires physical and/or chemical thin film deposition techniques, which typically involve high vacuum and high-temperature processes. In addition, masking and photolithography are necessary to define the desired device geometry. In contrast to those conventional device manufacturing technologies, innovative fabrication approaches for optoelectronic devices based on solution processing methods such as inkjet printing (IJP) have gained great momentum.

Semiconductor material inks for lead halide perovskites (LHPs) and lately lead-free perovskites (LFPs) can be prepared to deposit a wide array of functional materials in the form of precursor inks or nanoparticle colloidal suspensions. IJP is a digital material deposition technology, which means that the desired material stack can be printed in any pattern with precision without the need for masks. It also allows great control of process parameters and is ideal for fast prototyping while having the potential for scalability. Consequently, mass scale and cost-effective production of optoelectronic devices is possible by leveraging the maturity of IJP.

We will review the recent advances on IJP of LHPs and LFPs for optoelectronic devices of our group (UB) in the framework of the Drop it (EU) project. We will first introduce the inkjet printing, the test, and optimization of LHPs layers like CsPbBr₃. Secondly, we will introduce the layers produced with suitable electron/hole transport and blocking properties and with stable interfaces with the inkjet printed perovskites. For the electron injection, we have POT2T, SnO₂, ZnO transport layers and LiF/Al electrodes. For the hole injection, we have PEDOT:PSS, NiO_x and ITO electrodes. We will show how by engineering the layer stack we are able to produce green LEDs from active layers of CsPbBr₃ with luminance up to 10⁴ nits. Thirdly, we will present a summary of our best results in printing LFPs. Particularly, high quality and high-performance Sn-based 3D and 2D perovskites like FASnI₃, TEA₂SnI₄ and PEA₂SnI₄, and other compositions based in In and Cu like Rb₃InCl₆:Sb, CsCu₂I₃ and Cs₃Cu₂I₅. Finally, we will show devices like solar cells, waveguides, photodetectors, and red LEDs fabricated by inkjet printing of those LFPs.

Metal halide perovskite-based photovoltaics (PV) have been the major breakthrough in the PV field in the last decade.[1] Recently new perovskite compositions replacing the lead by other elements, such as Sn, Ge, Sb or Bi, has attracted attention to reduce the toxic lead. [2] In this talk, I will present the results of vacuum-deposited methylammonium bismuth iodide (MBI) and the advantages and drawbacks of the coevaporated-MBI thin-film fabrication.[3] Due to the lower efficiencies of lead-free perovskite solar cells (PSCs) in comparison with lead-based, I will present the design and cost analysis of lead-halide perovskite panel manufacturing in different locations.[4] In this work, five different device configuration will be evaluated, being the active layer less than 1% of the installed panel input energy. The key parameters, such as levelized cost of energy (LCOE), minimum sustainable price (MSP) and energy payback time (EPBT), will be presented. Differences between the locations were identified and they were mainly affected by the price of the local glass processing.

In this talk, a method to prepare optical quality films of ligand-free lead halide perovskite nanocrystals displaying quantum confinement effects by in situ preparation and processing within the void space of insulating porous matrices will be described.[1] The main photophysical properties of embedded quantum dots will be reviewed, with emphasis on the possibilities that the absence of organic ligands offer to achieve control over the optical and charge transport properties. Evidence of efficient dot-to-dot transport,[2] fast photoactivation,[3] high photoluminescence quantum yield (>85%), improved stability and enhanced durability,[4,5] with respect to their bulk counterparts, will be provided for different films made of MAPbI3, MAPbBr3, CsPbI3 , CsPbBr3 and FAPbBr3 quantum dots embedded in porous matrices. Overall, these results demonstrate that adequately designed networks of ligand-free perovskite quantum dots can be used as both light harvesters and photocarrier conductors, in an alternative configuration to those employed in previously developed QD optoelectronic devices.

Perovskite solar cells (PSCs) have achieved power conversion efficiencies (PCEs) > 25.7 %. State-of-the-art PSCs use passivation layers that protect cells from external agents such as moisture and remove surface defects. One of the most successful PSC uses large organic cations also used for the formation of 2D perovskite. Interestingly this surface layer can form in two modes: a heterostructure of low dimensional (2D) perovskite on top of a 3D absorber layer, or without the formation of a 2D perovskite. Both methods lead to highly efficient and stable perovskite solar cells, as it is possible to observe from research in the last five years.

Additionally, methods to form passivate or form 2D/3D heterostructures vary (spin coating, exfoliation, vapor, and vacuum deposition) and over 50 different ligands have been employed. This demonstrates the versatility of these cations.

This knowledge turns fundamental for device design, opening new strategies for perovskite interface optimization with a low cost and impact on the environment.

Lead halide perovskite nanocrystals are widely known for their optoelectronic properties such as outstanding molar absorption coefficients, high photoluminescence quantum yield and narrow band emission. Liquid crystal display industry has been widely introducing quantum dots (CdSe and InP based) in the last years in order to find an advantage against proliferation of OLED technology within more segments (laptops, tablets, tv sets). The usage of quantum dots enabled significant broadening of the color space that could be displayed, as well as improved the overall display brightness compared to OLED. Lead halide perovskites can enable even bigger technological advantages.

Restriction of Hazardous Substances (RoHS) directive introduced by the European Union set a standard, which also influences the display market. In fact Cd concentration in electronic components is limited to 100ppm, whereas In is beeing currently considered to be restricted due to its very high toxicity upon inhalation. Pb is a heavy element known for centuries and deeply studied. Its RoHS limit lies at 1000ppm (10x higher as Cd).

The presentation will show cases where lead halide perovskites can be applied and remain completely RoHS compliant

The interest in lead-free photovoltaics has driven a lot of research opportunities in the past decade, in particular, tin has been recognized as one of the most promising alternatives, exhibiting suitable optoelectronic properties, decreased toxicity, and good device performance with particularly high short-circuit currents. Nonetheless, the development of tin-based perovskites has been primarily hindered because of the ease of oxidation from Sn²⁺ into Sn⁴⁺, which promotes degradation mechanisms and compromises the long-term stability of the material.

Besides this intrinsic challenge, most studies have focused on spin coating as the main deposition method for the absorber layer, which is not compatible with large area manufacturing techniques like roll-to-roll or sheet-to-sheet. In this work, we explore blade coating and inkjet printing as versatile processes well-suited for commercial production; ink engineering of the solvent system and additives was used as a strategy to control the crystallization dynamics and obtain pinhole-free films on flexible substrates. Furthermore, the influence of processing conditions such as the coating speed, drying method, and waveform design on the perovskite morphology was analyzed. The potential industrial applicability of completed devices was tested through stability characterization after lamination and large area module fabrication.

We report a remarkably effective approach to passivating the copper cathode in inverted organo-tin halide perovskite photovoltaics, based on capping the cathode with a thin layer of a semi-metal. Using this simple approach unencapsulated photovoltaic devices retain 70% of their peak power conversion efficiency after up to 100 hours testing under continuous one sun solar illumination in ambient air and under electrical load. The semi-metal layer is shown to block corrosion of the copper cathode by iodine gas formed when those parts of the perovskite layer not protected by the electrode degrade, which we have previously shown to be a major source of device degradation in air [1]. The semi-metal layer is also shown to sequester iodine gas by seeding its condensation on top of the device, reducing the likelihood that it will ingress laterally through the electron transport layer photo-catalysing the degradation of the perovskite and corroding the buried cathode interface. It is envisaged that this electrode-based approach to improving device stability can be combined with any of the recently reported chemical approaches to improving the intrinsic stability of organo-tin halide perovskites in air.

The coherent spin dynamics in perovskite films:
Advantages of Sn-­‐based perovskites against Pb-­‐based perovskites.
G. Garcia-Arellano 1 , G. Trippé-Allard 2 , E. Deleporte 2 , F. Bernardot 1 ,
C. Testelin 1 and M. Chamarro 1
1 Sorbonne Université, CNRS, Institut des NanoSciences de Paris, 4 place Jussieu, F-75005
Paris, France
2 Laboratoire LuMin, CNRS, Université Paris-Sud, ENS Cachan, Université Paris-Saclay,
91405 Orsay Cedex, France
Hybrid metal-halide perovskites show outstanding optoelectronic properties and are also
highly promising materials in the spintronic domain due to their large and tunable spin-orbit
coupling, spin-dependent optical selection rules, and their predicted electrically tunable
Rashba spin splitting.
In this work, [1,2] we investigated the spin coherence time in a MAPI polycrystalline film by
means of a picosecond pump-probe technique: the photo-induced Faraday rotation (PFR). We
measured long spin coherence times of localized electrons (holes) of 4,4 ns (3,7 ns) at 1.635
eV and about 7 ns at 1.612 eV. We demonstrated that the spin relaxation time observed in the
PFR technique must be attributed to localized electrons and holes, instead of excitons as it
was supposed in previous work [3], due to: a) the long spin relaxation time, b) the linear
dependence on the electron and hole frequencies with the magnetic field confirming the
absence of electron-hole exchange interaction effects c) The possibility of tuning the electron
and hole contributions into the PFR signal by varying the energy of the pump-probe
experiment.
In more conventional semiconductor, like GaAs or CdTe, it has been demonstrated that the
two main mechanisms limiting, at low temperature and in the isolating regime, the value of
the electronic spin relaxation are the hyperfine interaction and the spin-orbit interaction. We
will discuss the consequences of replacing the Pb 2+ by Sn2+ cation on the spin decoherence
and relaxation times.
[1] Garcia-Arellano, G. et al, J. Phys. Chem. Lett. (2021),12, 8272.
[2] Garcia-Arellano, G. et al, Nanomaterials (2022), 12, (9), 1299.
[3] Odenthal, P. et al, Nature Physics (2017), 13, 894.

Lead-free metal halide perovskites (LFP) have emerged as a promising family of semiconductors to develop a new green technology for optoelectronics. This manuscript demonstrates that Cs2SnI6 (a vacancy ordered double perovskite) nanocrystals (NCs) present an extraordinary self-defocusing response not yet observed up to now. The near field characterization of nanosecond pulses traversing the cuvette filled by a solution of NCs indicates that there is a certain threshold of excitation intensity from which the width of the beam experiences a fast growth with the formation of the rings. Furthermore, the dependence of the traversing beam with the intensity and concentration of nanocrystals in the solvent indicates four different regions where the beam broads, diffracts on concentric rings or saturates. This complex behavior is reproduced by a nonlinear beam propagation method (BPM) incorporating a particular nonlinearity based on two saturation Kerr effects not observed up to now. The associated refractive index change indicates (Δn) a giant self-defocusing response, Δn=-0.05, whose magnitude is tunned with the intensity and concentration. Moreover, under certain conditions Δn exhibits a crossover from self-defocusing to self-focusing with the propagation distance, leading to a self-induced waveguide. This crossover between low-to-giant negative Kerr effect is perfectly reversible and can be explained by a laser trapping of NCs that increases the effective concentration of NCs.  The strong Kerr nonlinearity and this unexpected low-to-giant negative Kerr transition has never been observed and can be the base towards the optical signal processing fascinating opportunities in sensing and light–matter interactions for a future ecofriendly photonic technology.

Currently, there is a great demand for non-toxic lead-free perovskites as active materials for solar cells and light-emitting diodes (LEDs). In the first case, great progress has been made using 3D tin perovskites. At the same time, the search for a suitable lead-free perovskite material for LEDs is just at the beginning. From general considerations and by analogy with lead-containing perovskites, the most suitable structures for optoelectronic light-emitting devices should be 2D perovskites since they possess higher stability and high exciton binding energy resulting in high photoluminescence (PL) ability. An additional requirement from industry for such a material is a possibility to be manufactured by inkjet-printing on a flexible substrate. In this work, we have studied PL properties of chemically stabilized 2D perovskite thienylethylammonium tin iodide, (TEA)₂SnI₄, thin films of which were produced by inkjet-printing of precursors on a flexible polymer substrate (polyimide, PI). PL measurements performed in the 20–300 K temperature range made it possible to detect two equally narrow excitonic bands observed in the 630 - 665 nm region both in emission and absorption and exhibiting different dependences on the observation angle. In addition, m-PL mapping experiments indicate different spatial localization of radiation from these two excitons. Besides, amplified spontaneous emission and bi-exciton formation were detected at high intensity excitation at 20 K. All the above findings indicate high photophysical quality of thin (TEA)₂SnI₄ films inkjet-printed on flexible PI polymer that make them a promising non-toxic perovskite material for fabrication of efficient LEDs and microlasers.Currently, there is a great demand for non-toxic lead-free perovskites as active materials for solar cells and light-emitting diodes (LEDs). In the first case, great progress has been made using 3D tin perovskites. At the same time, the search for a suitable lead-free perovskite material for LEDs is just at the beginning. From general considerations and by analogy with lead-containing perovskites, the most suitable structures for optoelectronic light-emitting devices should be 2D perovskites since they possess higher stability and high exciton binding energy resulting in high photoluminescence (PL) ability. An additional requirement from industry for such a material is a possibility to be manufactured by inkjet-printing on a flexible substrate. In this work, we have studied PL properties of chemically stabilized 2D perovskite thienylethylammonium tin iodide, (TEA)₂SnI₄, thin films of which were produced by inkjet-printing of precursors on a flexible polymer substrate (polyimide, PI). PL measurements performed in the 20–300 K temperature range made it possible to detect two equally narrow excitonic bands observed in the 630 - 665 nm region both in emission and absorption and exhibiting different dependences on the observation angle. In addition, m-PL mapping experiments indicate different spatial localization of radiation from these two excitons. Besides, amplified spontaneous emission and bi-exciton formation were detected at high intensity excitation at 20 K. All the above findings indicate high photophysical quality of thin (TEA)₂SnI₄ films inkjet-printed on flexible PI polymer that make them a promising non-toxic perovskite material for fabrication of efficient LEDs and microlasers.

Metal halide perovskite nanocrystals (PNCs) can display excellent light emission properties, leveraging the chemical versatility of this family of materials.[1] However, using these features in functional films is an elusive task due to aggregation and material instability problems. Using a metal-organic host matrix based on a sol-gel approach allows for a controlled in-situ crystallization of perovskite nanocrystals with extremely low-demanding fabrication methods. [2] As a result, we have developed a straightforward, fast and antisolvent-free approach for the generation of high-performance nanocomposite thin films with photoluminescence quantum yield (PLQY) > 80% and outstanding ambient and mechanical stability. The crystallization dynamics determining the final nanoparticle size, and thus the emission properties, can be adjusted in detail through the ambient exposure and precursor concentration.

This in-situ PNCs nanocomposite synthesis for different MHP compositions approach may form the basis for the fabrication of large-area optoelectronic devices with enhanced properties, but also a groundwork on direct bandgap tunability through PNCs size’s crystallization dynamics control.

The development of energy-saving, up-scalable and high-throughput routes to synthesize metal halide perovskite-based materials (MHP) is one of the main challenges of making solar energy and lighting devices more economical and environmentally friendly. In this context, microwave (MW) radiation offers a promising approach to achieve high quality NCs of very different nature metals (Au, Ag), metal oxides (FeO, Mn₂O₃, and CoO) and semiconductors (CdS, CdSe, CuInS₂, and PbSe) in very short reaction times [1-3]. Since 2017, several pioneering works employed microwave radiation to promote the crystallization of halide perovskites nanocrystals [4,5].

This presentation will show some examples of lead-based perovskites prepared in our group using a microwave-assisted route. The main advantages of this methodology lie in the short reaction times facilitated by the homogeneous heating of polar solvents and reagents, or the elimination of complicated pre-synthetic procedures (several steps with controlled atmosphere and temperature). In the case of the benchmark all-inorganic perovskite CsPbBr₃, the reaction parameters were adjusted to prepare -in a one-step process and in just few minutes- uniform nanocrystals with a well calibrated morphology. After purification, these CsPbBr₃ nanocrystals exhibited excellent optoelectronic properties and enhanced stability. Indeed, LEDs have been fabricated with these MW-nanocrystals providing comparable performance to those prepared with hot injection-synthesized nanocrystals.

The work will also focus on the easy and high-throughput microwave-assisted preparation of a benchmark hybrid perovskite, α-FAPbI₃, as black powders, that can be used for solar cell fabrication. These MW-presynthesized powders can be stored in a glove box until use. They induce better crystallinity of the α-FAPbI₃ films in comparison with the conventional precursor solution method. Consequently, the solar cells fabricated from MW powders presented in average higher performance than conventional devices.

In conclusion, microwave radiation opens new strategies towards more sustainable development of perovskite solar cells.

SnO2 and NiO are  wide bandgap semiconducting metal oxides with applications in a variety of fields, including UV light sensing, gas sensing, and as a transparent conductor for LEDs and solar cells. Thanks to their wide bandgap energy, SnO2 and NiO are almost completely transparent to visible light, and thus ideal for UV detection. Metal oxides have traditionally been fabricated by physical and chemical deposition methods. Nevertheless, solution-processing approaches have gained prominence in the last years because of their versatility and controllability in layer deposition. In particular, technologies such as inkjet printing or spin coating enable controlled deposition of wide range of materials. 

 Inkjet printing is a digital deposition technique based on controlled ink ejection from a series of nozzles placed in printing head. As the printing head travels above the substrate, the ink is deposited in the form of a matrix of droplets in a specified pattern with high precision without the use of masks or photolithography. Despite these advantages, inkjet-printed layers are prone to surface irregularity.  In contrast, with spin coating a thin layer is achieved by spreading a certain amount of solution through high-speed substrate rotation. Even though better surface regularities are achieved through spin coating, it cannot control the deposition pattern.   

In this work, we compare the performance of high-quality inkjet-printed and spin-coated SnO2/NiO heterojunctions. Single layers of SnO2 and NiO deposited by both approaches are thoroughly studied by a variety of structural and optical techniques. SEM and profilometry show low surface roughness and a lack of pinholes. Optical absorption and conductivity measurements exhibited layers with good transparency and electrical conductivity. Heterojunctions combining these two metal oxides (ITO/SnO2/NiO/Ag),  , were fabricated using both techniques. A large current ratio between negative and positive polarizations was observed together with a notable UV photodetection. Thus, nkjet-printed devices show results comparable to spin coated ones.  These promising results showed that our inkjet-printed metal oxides are applicable to detect UV  as well as for use as transparent charge conductors for either LEDs or solar cells. 

Halide Perovskites (HPs) have attracted attention over the past decade mostly due to their excellent optoelectronic properties for multiple applications in the field of photovoltaics (PVs) and perovskite light-emitting diodes (PeLEDs) due to their low no-radiative recombination. Despite their enormous potentiality the Pb content of HPs reporting the higher performance for different electronic devices is limiting the entrance in the market of this materials.

This fact has originated an intense work on Pb-free HP alternatives with very promising results in the last years in the field of PVs but significantly more limited in LED field. The studies of the applications of Pb-free perovskite to LEDs is still demonstrated in few works. Specifically, the more important issue is the poor film forming property that strongly depends on the deposition method. 3D HPs present low exciton binding energies and the use of low-dimensional structures is preferred for the fabrication of PeLEDs. Among low-dimensional structures, 2D halide HPs are receiving interest due to their natural quantum well structures, small Stokes shifts, narrow emission FWHM and lifetime on the order of nanoseconds. As in the case of Pb-free HP PVs most promising family for the development of PeLEDs are Sn-HPs. Nevertheless, despite the considerable progress in terms of performance achieved (EQE and luminance), Sn²⁺ in its oxidation state is prone to undergo oxidation in ambient conditions, forming its tetravalent state Sn⁴⁺. This fact causes a p-type self-doping process, leaving undesired Sn²⁺ vacancies that act as nonradiative recombination centres, thus quenching the perovskite emission.

Beyond materials demands, development of Sn-free PeLEDs will require industrial friendly fabrication methods, as spin-coating, the usual approach for deposition of 2D-layered PeLED devices, is a technique difficult to upscale, as does not offer selective deposition of LEDs in large areas and waste most of the precursors. In contrast inkjet printing is an emerging technology suitable to achieve smooth, uniform and pin-hole free thin films able to produce low-cost, large-area and even foldable-devices. Since its early beginnings, inkjet printing has attracted the attention of many researchers in the perovskite materials field, as it is believed to be the most feasible tool of patterning full color QD-LED display for mass production. This technique is especially attractive for the fabrication of LEDs arrays over large areas. Here, we present as the evolution from the first fabrication of Pb-Free HP PeLED i) on flexible substrate and ii) by inkjet printing deposition of the active layer. PeLEDs based on 2D PEA₂SnI₄ (PEA, phenyl ethyl ammonium) and TEA₂SnI₄ (TEA, 2-tiopheneethylammonium) have been fabricated by inkjet-printing technology, on both glass and polyimide flexible substrates, with red emission (630 nm for PEA₂SnI₄ and 640 nm for TEA₂SnI₄). Effect of using green solvent engineering in Sn-based perovskite LEDs will be also analyzed. Moreover, several additives can play an important diferent role in stabilization of both Sn-based red amitting LEDs.

Lead halide perovskites (LHPs) have shown outstanding optical emissive properties and can be used in displays, either as color conversion layers (CCLs) or self-emissive light emitting diodes (LEDs). Well‑established technologies (OLEDs, MicroLEDs) are either prone to degradation or require expensive materials and technology. Inorganic LHPs are demonstrating to be more stable than their organic counterparts wherein higher efficiencies are displayed for spin-coated devices. In this work, we propose inkjet printing as an industrial-friendly technique to deposit LHPs as a method for producing low-cost, large-area CCL and LEDs. We have developed inks from colloidal nanocrystals of CsPbBr₃. Subsequently, inkjet printing parameters have been optimized to allow thin layer deposition with a strong emission. CsPbBr₃ printed layers emit at 524 nm with a narrow emission of an FWHM about 15 nm [1].

Exploiting these results, we propose the fabrication of green-emitting LEDs based on CsPbBr₃ in ambient conditions by inkjet printing. In this work, several inverse structural (p-i-n) configurations are tested in order to investigate the influence and role of the selected transport layers. We emphasize the significant contribution of inkjet-printed (IJP) NiO onto the commonly used hole injection material poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) to increase device performance and stability. Even though with challenging crystallization dynamics for IJP technology, our devices with IJP NiO show excellent performances similar to devices with widely used spin-coated organic EBL layer (poly [bis (4-phenyl) (4-butylphenyl) amine i.e., Poly-TPD). Thus, inkjet-printed CsPbBr₃ LEDs incorporating NiO as EBL yields increased luminance (10000 cd m⁻²) with a turn‑on voltage of ~ 5 V and an external quantum efficiency of ~ 3%. Furthermore, the shelf-life of these devices will also be analyzed. Thereupon, this work constructs the initial steps towards stable fully inkjet‑printable perovskite light-emitting devices for a wide variety of low-cost and customizable applications.