Perovskite solar cells have come to the forefront of solar research in the last decade with certified efficiencies of now >26%. This is approaching rapidly the Shockley-Queisser limit for single-junction solar cells, implying that the main breakthroughs for perovskites were achieved with relatively narrow bandgaps.[1a,1b] Less progress, however, was made for wider bandgap perovskites, which are of interest for multijunction photovoltaics, detector applications, or water splitting. These wide bandgap perovskites are often comprised of fully inorganic components, which are hard to dissolve in conventional solvent systems and require more sophisticated synthesis as well as crystallisation techniques.

In this talk, I will discuss strategies to address these challenges by providing a library of hitherto unexplored wider bandgap perovskites using combinatorics. Mechanosynthesis is then studied to attain otherwise inaccessible liquid precursors permitting the realization, e.g., of “triple cation” wide bandgap perovskites.[2]

Unfortunately, the newly formulated liquid precursors often exhibit complex crystallization behaviour struggling to expel the typically used DMSO solvent. To delay the crystallization time, two strategies are proposed to remove the strongly complexating DMSO molecules through a) modified processing of the liquid thin-film[3] and b) a coordination solvent with a high donicity and a low vapor-pressure[4] leading to a marked improvement in the overall film quality.

Lastly, interface manipulation, especially on top of the formed perovskite, is becoming a central topic to advance further. Typically, this involves chemical surface treatments with a complex interaction. Here, light annealing is introduced as a universal, non-chemical approach to modify the perovskite surface resulting in a reduced surface recombination.[5]

[1a] Saliba et al. Energy & Environmental Science (2016), [1b] Turren-Cruz, Hagfeldt, Saliba; Science (2018)

[2] Ferdowsi,…, Saliba ; Chemistry of Materials (2021)

[3] Byranvand,…, Saliba; One‐Step Thermal Gradient‐and Antisolvent‐Free Crystallization of All‐Inorganic Perovskites for Highly Efficient and Thermally Stable Solar Cells, Advanced Science (2022)

[4] Zuo,…, Saliba; Coordination Chemistry as a Universal Strategy for a Controlled Perovskite Crystallization, Advanced Materials (2023)

[5] Kedia,…, Saliba; Light Makes Right: Laser Polishing for Surface Modification of Perovskite Solar Cells, ACS Energy Letters (2023)

     Perovskite nanocrystals (NCs) such as those made from CsPbBr₃ have numerous uses. Most involve exploiting their light emission and are motivated by their defect tolerance and large, as-made emission quantum yields (QYs). For the latter, near unity QYs are possible. This leads to ready applications as light emitters but also intriguingly to possible material platforms for demonstrating semiconductor-based optical refrigeration.

     Absent, though, is a fundamental understanding of perovskite NC emitting states, central to these applications. Of particular note are observations of near-universal, size-, temperature-, and composition-dependent absorption/emission Stokes shifts where observed energy differences are those that separate absorbing and emitting states. Moreover, efficient (near-unity efficiency), photoluminescence up-conversion, induced by exciting NCs below gap, motivates better understanding the microscopic nature of perovskite band edge states.

     I will explain work we have done recently within the context of attempts to optically refrigerate a semiconductor. These studies now provide new insight into the band edge states of CsPbBr₃ (and possibly CsPbX₃) NCs. Starting with a microscopic mechanism for explaining how it is possible to obtain efficient, near-unity efficiency photoluminescence up-conversion to we extend the conclusions of these measurements to explain the origin of observed, size-dependent absorption/emission Stokes shifts. Here, despite some initial studies we and others have conducted, very little is known about their true origin. This is to be contrasted to more conventional NCs such as CdSe where band edge exciton fine structure quantitatively accounts for both global and resonant Stokes shifts, with emission emerging from a dark exciton. Although similar perovskite NC fine structure might account for their shifts, both theory and experiment predict bright/dark fine structure splittings easily an order of magnitude too small to account for experiment.

     We now propose that perovskite NC emitting states are polarons, which result from the lattice accommodation of photogenerated charges. Polaron binding energies and lifetimes are, in turn, suggested to be the origin of observed l-, T-, and composition-dependent absorption/emission Stokes shifts and excited state lifetimes. This represents a significant departure from more conventional descriptions of NC band edge states, which exclusively involve exciton fine structure and dark exciton emitting states.

Halide Perovskite Photovoltaics are on the brink of commercialization and after having achieved high performance, the stability, scalability, and sustainability of the technology are now the most important technological challenges to overcome. Halide perovskites being versatile in terms of their processability, there are many options for the development of scalable processing technology. Solution processing based on slot-die coating and inkjet printing are two promising options with their respective design advantages and opportunities.

The development of precursor inks that allow reliable and sustainable processing is one of the most important challenges we are tackling. Our team's current efforts in this domain focus on three major aspects:

Accelerated ink and process optimization by combinatorial processing approaches: We are employing innovative combinatorial processing techniques based on inkjet printing and slot-die coating to expedite the optimization of precursor inks and associated manufacturing processes.

Exploration of Green Solvent Alternatives with Extended Ink Shelf-Life: In our commitment to sustainability, we are investigating environmentally friendly solvent alternatives. Our focus extends beyond performance considerations to include the development of green solvents that not only meet performance standards but also contribute to an extended ink shelf-life. This dual emphasis on performance and longevity is crucial for practical implementation and large-scale production.

Collaborative Data Management: Based on ongoing efforts of the PerovskiteData base Project, we are introducing Research Data Management Tools that can easily be adapted and multiplied by the entire research community. This collaborative approach facilitates efficient decision-making and accelerates the iterative optimization process.

By addressing these challenges head-on, our research aims to contribute to the acceleration of the deployment and utilization of Perovskite Photovoltaics for power generation.

Hybrid organic-inorganic perovskite materials have gained emphasis in worldwide photovoltaic (PV) research, particularly due to their impressive power conversion efficiencies (PCEs) above 26% as well as their potential of becoming a candidate for inexpensive mass production¹. Perovskite-based research today is mostly on thin layer solution based deposition techniques given their potential for integration into semitransparent. However, integration of this approach into windows and buildings is challenging as homogeneity, reproducibility, yield, and other aesthetic relevant characteristics required for building integration market have not been demonstrated to a satisfactory level. As an alternative, three-layered dielectric/metal/dielectric (DMD) thin film sequences have been successfully employed in perovskite-based research resulting in comparable PCEs up to 15%², superior average visible transmittance (AVT), and good light utilization efficiency (LUE)³, defined as the product between AVT and PCE, highlighting the great promise of transparent electrodes. Here, we have studied semi-transparent DMD electrodes based on WO₃ and Ag, to boost the PCE in semi-transparent formamidinium lead halide solar cells. A screening upon the mixed halide perovskite, from pure bromide to pure iodide has been made, demonstrating that the PCE increases with the semi-transparent electrode compare to the conventional semi-transparent Au. This work demonstrates the potential use of semi-transparent electrode to improve the light harvesting of the perovskite layer, by using optical methods to compensate chemical limitation, paving the way for application in building integration. It is proved herein that semitransparent electrodes with WO3 of 40 nm allows for the fabrication of solar cells covering a wide bandgap regime ranging from materials with suitable bandgaps for single-junction solar cells (FAPbI3, Eg = 1.5 eV) to wide bandgap materials (FAPbBr3, Eg = 2.3 eV). The solar cells prepared with this approach give promising results that compete well with more intricate fabrication approaches previously reported, while at the same time current and aesthetic parameter like Average Visible Transmittance (AVT) and Light Utilization Efficiency (LUE) are increased to real building relevant values.

Halide perovskites have been under the focus for photovoltaic applications where their power conversion efficiencies have soared to efficiencies exceeding 26%. They have also garnered tremendous research interest over recent years for the development of next-generation light-emitting diodes and detectors. The spotlight on this class of semiconducting material stems from several of its enviable traits such as long carrier diffusion length, defect tolerance, high colour purity, and spectral bandgap tunability which spans across the visible and infrared spectrum. This talk will cover our recent efforts in utilising the ionic characteristics of halide perovskites to enable memristive devices that can be employed for neuromorphic applications. The talk will cover 2 and 3 terminal memristive devices as well as our efforts to utilise colour changing LEDs and photovoltaic devices as unconventional computing elements.

The family of Sn-perovskite has recently emerged as a nontoxic compound for a future ecofriendly photonic technology. With an extraordinary quantum yield of emission at room temperature, bandgap tunability with the composition, and straightforward incorporation in optical architectures by chemistry methods, the ASnX₃ (A is an organic/inorganic anion and X is a halide) perovskite represents a suitable nontoxic material to implement lasers, optical amplifiers or light emitting diodes, among other devices. However, since Sn²⁺ is easily oxidized into Sn⁴⁺ losing its optoelectronic properties, there are few reports where a stable ASnX₃ device is provided. In this work, high-quality FASnI₃ (FA, formamidinium) polycrystalline thin films are successfully fabricated to demonstrate optical amplification and lasing. With an appropriate low temperature treatment and a polymethylmethacrylate(PMMA) clapping, the FASnI₃ films exhibit a remarkable stability and an efficient generation of amplified spontaneous emission (ASE) under nanosecond optical pumping. First, these films are deposited on a SiO₂ substrate to conform an optical waveguide whose geometrical parameters (i.e. thicknesses of the films) are properly designed to optimize the excitation and to enhance the generation of the photoluminescence. As a result, ASE is demonstrated with an extremely low threshold, about 100 nJ/cm², and a strong polarization anisotropy preferable to the transverse electric (TE) polarization. Moreover, the waveguide exhibits narrow lasing lines (< 1 nm) caused by the formation of random cavity loops in the polycrystalline grains. Then, the same structure is implemented in a flexible device using polyethylene terephthalate (PET) substrates. Here, despite that the formation of films formation of films on a flexible platform is always challenging, the flexible waveguide also shows ASE and RL lines with only one fold higher threshold (1 µJ/cm²). Finally, the FASnI₃ films are also incorporated as active medium in a Distributed Feedback Laser properly designed to achieve optical resonance at the ASE wavelength. This architecture  conforms an optical cavity able to demonstrate the generation of lasing action with peaks narrower than 1 nm. The proposed devices represent an important step towards the development of future cheap and green photonic technology based on Sn perovskites.

Metal halide perovskites are of immense importance due to their excellent optoelectronic properties, holding great promise in the field of advanced and clean energy technologies. One of the fundamental mechanisms governing their physical properties is the interplay of electron-phonon coupling with the strong lattice anharmonicity and their inherent locally disordered structure [1,2]. To understand the consequences of these effects, we have recently introduced a powerful theoretical framework that allows to capture anharmonic electron-phonon coupling in these intrinsically polymorphous compounds [3,4]. In this talk, I will demonstrate our methodology for both inorganic and hybrid halide perovskites and show that (i) local disorder is at the origin of overdamped and strongly coupled anharmonic phonons, (ii) low-energy optical vibrations dominate electron–phonon renormalized band gaps, departing from a simplified picture of a Fröhlich interaction, and (iii) local disorder is the key to explain the monotonic increase of the band gap across phase transitions. Our work provides a new perspective for the interpretation of perovskite materials fundamentals as well as opens the way for efficient simulations of halide perovskites' key properties, like carrier mobilities, excitonic spectra, and polaron physics.

Lead and tin halide perovskites are currently under intense investigation for their potential applications in optoelectronics, due to their favorable and adjustable semiconducting properties. One of the key advantages of perovskites lies in their ability to be deposited as thin films using energy-effective techniques, resulting in high-quality semiconductors. Despite the potential for widespread adoption in the industrial sector, vacuum deposition of perovskite films and devices remains a specialized area. Here we will examine the latest developments in the vacuum deposition of perovskite films, focusing on methods to manipulate their morphology and structure. Specifically, we will highlight the impact of factors such as composition, deposition rate, and substrate temperature on properties like luminescence quantum yield and recombination lifetime. Lastly, we will explore the use of multilayer semiconducting structures in single-junction solar cells and photodetectors.

The dynamic response of metal halide perovskite devices shows a variety of physical responses that need to be understood and classified for enhancing the performance and stability and for identifying physical behaviours that may lead to developing new applications. A multitude of chemical, biological, and material systems present an inductive behavior that is not electromagnetic in origin, termed a chemical inductor. We show that the structure of the chemical inductor consists of a two-dimensional system that couples a fast conduction mode and a slowing down element. The impedance spectra announce the type of hysteresis, either regular for capacitive response or inverted hysteresis for inductive response. We develop the methods to characterize time transient and photocurrent response to a voltage pulse. We can obtain important control of the time constant that determine hysteresis. We apply these insights in kinetics processes to the development of memristors and neurons. Overall we provide a method to determine important kinetic responses of the halide perovskites that can be aused in many different applications.

Perovskites, especially Pb-free tin halide perovskites, show promise for efficient optoelectronic/electronic microsystems and image sensors, fabricated through simple techniques like inkjet printing. This approach aims to reduce device costs globally, cater to various applications, and decrease reliance on current semiconductor technologies. In this work we anticipated innovations with 2D and 2D/3D tin halide perovskites which have the potential to become commercially viable products, addressing the evolving needs of a digital society while promoting sustainability and reducing dependence on existing semiconductor technologies.

Along the work we have proposed and tested experimentally (chemical synthesis and basic structural and optical properties) many perovskite and perovskite-like materials. From them, we focused on several of them: i) 2D/3D perovskite compounds (R0.5,BA0.5)2FA9Sn10I31 with  R = PEA, TEA, DIP cations for allowing crystallization and stabilize the tin-perovskite phase for inkjet printing deposition techniques; ii) FASnI3  with additives and light soaking was further used for spin-coated films used in the optimization of vertical lasing structures;  iii) PEA2SnI4SnI4 and TEA2SnI4 for red emitting LEDs and photonics (emitting devices and photodetectors); Cs3Cu2Cl5 and Rb3InCl6:Sb for blue and green LEDs.

In photovoltaic devices, important advances were achieved: world record efficiency for flexible lead-free perovskite solar modules of 5.7 % under 1-sun and an impressive 9.4% for 2000 lx, indicating their potential for indoor applications. This was possible through the in-situ synthesis of SnI2 from metallic tin and iodine in a DMF:DMSO solvent.

For lead-free LEDs: (i)-(ii) First inkjet-printed Pb-free perovskite LED emitting at red wavelengths and first on a flexible substrate with commom DMF and sustainable DMSO solvents.

In photonics applications several advances were achieved: (i) ASE/lasing action and near single-mode operation were observed over a threshold of 200 µJ/cm2 for inkjet-printed films of 2D/3D G-LFPs, which is close to that obtained with the counterpart device implemented with the 3D FASnI3 film deposited by spin-coating; (ii) This 2D/3D G-LFPs also exhibits good performances for low-level light photodetection: responsivity as high as 50 A/W was measured after one month at 450 nm in encapsulated devices, with an estimated (using dark current value) detectivity better than 8.1010 Jones; flexible photodetectors exhibit comparable performances. (iii) inkjet-printed films of 2D tin-perovskites (TEA2SnI4 among them) are exhibiting efficient two photon absorption mechanism at room temperature and also leading to efficient photodetectors in glass and PET substrates with very low dark currents.

The proposed eco-friendly devices should be taken into account in future advances for scalable flexible optoelectronic Sn-based applications.

The pursuit of efficient and stable perovskite solar cells (PSCs) has propelled investigations into the nuanced realm of charge extraction dynamics. This presentation delves into the comprehensive exploration of charge extraction effects on the efficiency and stability of PSCs, encompassing the intricacies associated with mixed organic-inorganic, inorganic, and lead-free perovskite types. Special attention is devoted to the burgeoning topic of self-assembled monolayers (SAMs), with a focus on the critical role played by hole and electron-selective SAMs in tailoring charge extraction processes [1].

A focal point of our study involves the application of time-resolved surface photovoltage (TR-SPV) as the principal methodology. TR-SPV emerges as a novel and powerful technique, enabling the elucidation of charge dynamics within the remarkably short time scale of 1 nanosecond to 100 milliseconds. Through this method, we unravel the subtle intricacies governing charge extraction, shedding light on the temporal evolution of carrier behavior at the interface [1,2].

The discourse spans an investigation into the influence of various perovskite compositions and structures on charge extraction mechanisms. Our exploration includes a detailed analysis of mixed organic-inorganic, purely inorganic, and lead-free perovskite solar cells [3]. Additionally, we delve into the role of SAMs in modulating charge extraction dynamics, offering insights into their tailored design for enhanced PSC performance.

As a testament to the practical implications of our findings, this presentation culminates in the demonstration of a PSC device exhibiting exceptional stability. The device, subjected to rigorous testing, showcases remarkable resilience, maintaining its structural and functional integrity for an unprecedented 3000 hours without any discernible signs of degradation. This endeavor not only advances our understanding of charge extraction dynamics but also underscores the potential for achieving prolonged stability in perovskite solar cell technology.

Recent discoveries have revealed a breakthrough in the field using inorganic-organic hybrid layers called perovskites as the light harvester in the solar cell. The inorganic-organic arrangement is self-assembled as alternate layers, being a simple, low cost procedure. These organic-inorganic hybrids promise several benefits not delivered by the separate constituents.

In this work we present a fully printable mesoporous indium tin oxide (ITO) perovskite solar cell. The solar cell structure consists of triple-oxide screen-printed mesoporous layers. In this structure, the perovskite is not forming a separate layer but fills the pores of the triple-oxide structure. The perovskite is utilized as both the light harvester and a hole transporting material. One of the advantageous of this solar cell structure is the transparent contact (mesoporous ITO) which permit the use of this cell structure in bifacial configuration without the need for additional layers or thinner counter electrode. We performed photovoltaic (PV) measurements on both sides (i.e. ITO-side and glass-side), where the glass side show 15.3% efficiency compare to 3.8% of the ITO-side. Further study of the mechanism shows that the dominant mechanism when illuminating from the glass-side is Shockley-Read-Hall recombination in the bulk, while illuminating from the ITO-side show recombination in multiple traps and inter gap defect distribution which explain the poor PV performance of the ITO-side. Electrochemical impedance spectroscopy shed more light on the resistance and capacitance. Finally, we demonstrate 18.3% efficiency in bifacial configuration. This work shows a fully printable solar cell structure which can function in bifacial configuration.

Halide perovskite solar cells (PSCs) have already demonstrated power conversion efficiencies above 26%, which makes them one of the most attractive photovoltaic technologies. However, there are several challenges must be overcome for the technology to be competitive and commercially available. One of the main bottlenecks towards their commercialization is their long-term stability, which should exceed the 20-year mark. Several are the strategies currently employed to stabilize PSCs, for example, the use of complex metal oxides as transport layers, the passivation of defects in the halide perovskite layer through additive engineering, or the replacement of metal electrodes by carbon-based electrodes, etc. Among these, additive engineering is an effective pathway for the enhancement of device lifetime. Additives applied as organic or inorganic compounds, improve crystal grain growth enhancing power conversion efficiency. The interaction of their functional groups with the halide perovskite (HP) absorber, as well as with the transport layers, results in defect passivation and ion immobilization improving device performance and stability. In this talk, we will briefly summarize the different types of additives recently applied in PSC to enhance not only efficiency but also long-term operational stability. We discuss the different mechanism behind additive engineering and the role of the functional groups of these additives for defect passivation. Special emphasis is given to their effect on the stability of PSCs under environmental conditions such as humidity, atmosphere, light irradiation (UV, visible) or heat, taking into account the recently reported ISOS protocols. We also discuss the relation between deep-defect passivation, non-radiative recombination and device efficiency, as well as the possible relation between shallow-defect passivation, ion immobilization and device operational stability. We will also show our most recent results applying additives in PSC where we have been able to obtain efficiencies above 21 % and highly stable devices showing null degradation after more than 10000 h under continuous light irradiation of 1 sun.

REFERENCES

[1]     M. V. Khenkin, E.A. Katz, et al., M. Lira-Cantu, Nat. Energy 5 (2020) 35–49.

[2]     H. Xie, M. Lira-Cantu, J. Phys. Energy 2 (2020) 24008.

[3]     A. Mingorance, et al., Adv. Mater. Interfaces 5 (2018).

[4]     M. Lira-Cantú, Nat. Energy 2 (2017) 17115.

[5]     A. Pérez-Tomas, Sustain. Energy Fuels 3 (2019) 382–389.

[6]     H. Xie, et al., Submitted (2020).

[7]           C. Pereyra, H. Xie and M. Lira-Cantu. J. Energ Chem. 2021

Perovskite solar cells (PSC) are highly promising candidates for future space photovoltaics due to their high specific power potential. Yet, for successful application, devices need to resist several sets of extremes in space. In this presentation we will discuss their extraordinary radiation tolerance [1]–[3] and then move on to extreme temperatures and temperature cycles, two extremes that perovskites are well suited to. Atomic oxygen (AtOx), on the other hand, corrodes unencapsulated PSCs swiftly, as we identify. And while we find that this can be avoided using ultrathin evaporated 0.7 µm silicon oxide (SiOx) barriers, we set out to understand the AtOx-induced degradation mechanisms of phenethylammonium iodide (PEAI)-2D passivated and non-passivated devices. Surprisingly, degradation is more severe in 2D passivated PSCs. To disentangle damage mechanisms between 2D passivated and non-passivated devices we apply injection-current-dependent electroluminescence (EL) and intensity-dependent photoluminescence quantum yield (IPLQY) measurements. These allow us to derive pseudo-JV curves that are independent of parasitic resistance effect from damaged transport layers. We quantify an implied FF, that remains high after degradation suggesting that the perovskite bulk is not severely degraded. On the other hand, GIWAX studies reveal a degraded surface that limits charge extraction, and thus leads to lower performance metrics. This surface degradation is severely accelerated for 2D passivations and proceeds to areas that are covered by copper contacts due to lateral diffusion of AtOx though the 2D surface owing to the large interplanar distance of 2D perovskites.

[1]      F. Lang et al., “Efficient minority carrier detrapping mediating the radiation hardness of triple-cation perovskite solar cells under proton irradiation,” Energy Environ. Sci., vol. 12, no. 5, pp. 1634–1647, 2019, doi: 10.1039/C9EE00077A.

[2]      F. Lang et al., “Proton‐Radiation Tolerant All‐Perovskite Multijunction Solar Cells,” Adv. Energy Mater., vol. 11, no. 41, p. 2102246, Nov. 2021, doi: 10.1002/aenm.202102246.

[3]      F. Lang et al., “Radiation Hardness and Self-Healing of Perovskite Solar Cells,” Adv. Mater., vol. 28, no. 39, pp. 8726–8731, Oct. 2016, doi: 10.1002/adma.201603326.

All-inorganic cesium lead triiodide (CsPbI3) perovskites show high potential for photovoltaic applications due to their excellent thermal stability and suitable bandgap (Eg≈1,72 eV) ideal for tandem device. However, the photovoltaic performances of CsPbI3 perovskite solar cells (PSCs) are significantly restricted by a scarcely controllable crystal quality leading to high nonradiative recombination processes [1]. Therefore, the potential of CsPbI3 is overshadowed by the black-phases (α, β, and γ) structural instability, prone to spontaneous evolution into the photoinactive δ-phase at room temperature. This transition can be accelerated by ambient moisture, resulting in diminished PCE. Consequently, stabilizing black CsPbI3 at room temperature has become a critical topic. The regulation of the nucleation and growth rates has been identified as an efficient strategy for enhanced film coverage [2]. CsPbI3 perovskite films are produced via a cost-effective and straightforward solution-based manufacturing process. However, the nucleation and growth processes are largely uncontrollable, leading to inevitable defects stemming from conventional coating methods. Understanding the fundamental mechanism underlying film formation, specifically in terms of nucleation and growth, is crucial. Identifying this mechanism is a necessary step for precisely adjusting film crystallization kinetics. The optimization of additive engineering has proven to be a successful and straightforward approach in developing Cs-based photovoltaic devices with enhanced efficiency and stability. Consequently, it has emerged as a significant focus in PSC (perovskite solar cell) research. The aim of this work is to obtain a stable CsPbI3 polycrystalline thin film modulating the different parameters involved in the solution processing of the films, spanning from the employed solvent to the use of additives modifying the solution chemistry, to the use of alternative Pb sources DMAPbI3 [3]. The chemistry involving additives currently revolves around the utilization of HI and DMAI [4,5] within the precursors salts solution. Experimental evidence in both scenarios substantiates the formation of the intermediate DMAPbI3 within the solution, HI reacts with DMF and DMAI with PbI2. By synthesizing DMAPbI3 through hydrolysis and utilizing it directly as a lead source in the solution, it's possible to achieve better stoichiometric control involving DMA+ and to produce higher-quality films.The formation of intermediate complexes during the crystallization process assumes a pivotal role. For instance, the inclusion of additives, such as Cl− ions in the precursor solution has a positive impact on the nucleation of perovskites. Importantly, these Cl− ions aid in the nucleation process without becoming part of the perovskite lattice structure itself. This, in turn, leads to the production of perovskite films with enhanced optoelectronic properties, suggesting an improvement in their ability to interact with and respond to light. The presented strategies allow to investigate the effect on the nucleation process and how the existence of solute–solvent crystalline intermediate phases have an impact on chemical reaction kinetics. Finally, the optimized films have been integrated and tested in solar cells.

Metal halide perovskite (MHP) semiconductors are excellent candidates for contemporary optoelectronics innovation, particularly for photovoltaics.[1] The advantages of this class of materials derive from their hybrid nature, allowing for straightforward fabrication processes, and from their unique optoelectronic properties. A typical 3D organic-inorganic perovskite has a chemical formula of ABX3, where A is an organic cation (such as MA [methylammonium] or FA [formamidinium]), B is a metal cation (such as Pb2+), and X is a halogen anion (such as I or Br).[2] However, recent advances have also explored more complex compositions embedding diverse cations/anions.[3] These materials are prepared by simple and straightforward solution processing, the material precursors dissolved in a solvent undergoes self-assembly into a perovskite structure during spin-coating onto a substrate under mild thermal annealing.

As the technology continues to mature, this still is a key advantage, allowing for affordable and scalable processing. Understanding perovskite ink properties is therefore a fundamental requirement towards industrialization, with special regards to their evolution over time.

It has been demonstrated that even for the simplest system, the precursor solution is a complex – and dynamic – dispersion which contains not only solvated ions but also lead halide complexes, colloids and aggregates of different natures and dimensions. In these complex dispersions, multiple chemical species are present and can interact – or react – between each other or with the solvent.

We have proved the existence of a reactivity between two of the perovskite components – MA and FA – in the precursors solutions, that leads to the formation of a novel condensation product, methylformamidinium (MFA). We have studied different parameters that affects such reactions kinetics, therefore modifying the ink composition over time, and proposed solutions to overcome these issues.[4]  With the aim of correlating the solution chemistry with the film structural properties, through the synergic use of solution Nuclear Magnetic Resonance (NMR) spectroscopy, X-ray Diffraction and Density Functional Theory (DFT) calculations, we have recognized and explained for the first time a correlation between the aging of perovskite precursor solutions, the presence of MFA species in solution and the emergence of photoinactive hexagonal polytypes (6H and 4H) [5]

Starting from the known reactivity of the chemical species present in ink solutions, we outline the directions towards which future research efforts should be directed.[6]

Perovskite on silicon (Si) tandem solar cells are predicted by the ITRPV to be the first Si-based tandem solar cells to enter the market. Their superior power conversion efficiency promises a step change in module efficiency that is not possible with silicon only technologies, as shown by Oxford PV’s recent certified world record of 28.6% in a full area cell. With its integrated pilot line at Brandenburg, Germany, Oxford PV is currently ramping up to high-volume production of commercial M6 tandem wafer product.

Perovskite tandem commercialisation has taken place in a very short period of time compared to other photovoltaic technologies. This rapid progress has been possible due to the development of in-house protocols and the statistical analysis of the large datasets generated. Some of the advanced characterisation at Oxford PV and how they inform decision making on process and technology designs in view of cell efficiency and longevity targets will be presented. The measurements can be categorised according to their speed, the complexity of data analysis and the value of the measured parameters – increasing measurement speed and analysis allows for more insights on more samples more frequently, and so a key part of industrial solar R&D involves innovations on measurement protocols. In this talk, there will be examples of the advanced characterisation suite that have developed at Oxford PV to maximise the learning for as many samples as possible whilst focusing on the most important parameters, and eliminating redundancies. Upon generation of high quality datasets, machine learning tools are used to improve our statistical understanding of trends we see with development of the Oxford PV tandem cell technology. As well as cell efficiency enhancements, these complimentary research methods are just as suited for improving cell reliability, for which the perovskite field has made good steps in the last 12 months in aligning on predictive accelerated stressing protocols. The big data approach is also suitable for identifying process sensitivities in view of designing scalable processes, a critical part of R&D in an industrial setting.

Finally, sustainability, both in financial and ecological terms, is a crucial aspect of manufacturing at large scale. Leveraging advanced characterisation and machine learning can expedite from small scale proof of concepts towards achieving comparable KPIs with high-TRL production ready processes. Oxford PV is committed to bring to the market the most sustainable technology in the most sustainable way; examples of the initiatives Oxford PV has implemented to make that happen will be presented.