Metal halide perovskites are a highly divers class of materials due to their wide range of compositions and the varying dimensionality of their metal halide sublattices. These differences are also reflected in the physicochemical properties of these materials which can be further tuned by controlling the crystal growth process. Understanding how the fundamental properties of metal halide perovskites are influenced by these parameters is vital in order to improve them for use in different applications. This chapter reviews the state of the art of metal halide perovskites considering the latest experimental as well as theoretical studies. We describe in depth the different structures of perovskites taking into account their composition as well as the dimensionality of the metal halide sublattice. From this we derive the general electronic structure of these materials and discuss its interplay with their crystal structure. The thermodynamic stability of metal halide perovskites with regard to phase transformation and decomposition and the influence of composition, preparation methods and defects on this crucial property are additional key points in this chapter. All this information is presented to illustrate how the properties of metal halide perovskite materials can be tuned to optimize device performances.

Everyday healthcare objects have become the focus of interdisciplinary research lines, which aim to monitor human biomedical parameters by means of ergonomic and, ideally, environmentally sustainable sensors. Here, a hybrid system, based on both solution-processed- and conventional silicon-technology, is reported. In particular, a strain and a pH sensor are developed based on graphene inks, while a humidity detector is implemented using a poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS). The printed sensors are integrated into a demonstrator consisting of a silicon near field communication (NFC) transponder chip with logic and transceiver capabilities, bonded on a circuit board with inkjet-printed components on a paper substrate: an antenna and a power supply (in addition to the sensor). This proof-of-concept seeks to address the needs for a future circular economy, as well as those for cheap, flexible, and lightweight, multi-functional electronics.

Defects in polycrystalline halide perovskite films can cause a decrease of the solar cell photoconversion efficiency and stability. The perovskite film enhanced during crystal growth by controlling the processing method can alleviate defects and the related recombination sites that affect the performance of cells. Herein, flash infrared annealing is employed to crystallize methylammonium lead iodide perovskite with a single heating pulse, where uniform grain domains are optically observed and mapped. Films are annealed with different temperature ramps up to 48 °C s−1 heating rate. Annealing with higher heating rates presents lower defect densities, decreases the Urbach energy tail, and improves the optoelectrical performance of the films. These improvements are rationalized by Raman spectroscopy of nucleation points and grain surface differences among the process variations. The role of crystal growth and subsequent film quality allows to achieve a champion photovoltaic device growth at 48 °C s−1 with stability around 250 h under 1 sun illumination and 60% relative humidity for 100 h under 3 sun (AM1.5G) illumination. In situ optical imaging is recorded during the process, confirming that rapid annealing, i.e., higher heating rates, contributes to obtain more stable devices with the added advantage of shorter processing time.

In this work, we elucidate the relationship between heating-rate and FAPbI3 perovskite phase transformation, bringing a new relationship with crystal growth parameters. Thus, we manufactured highly stable perovskite solar cells with a 640 ms IR pulse.

Cost management and toxic waste generation are two key issues that must be addressed before the commercialization of perovskite optoelectronic devices. We report a groundbreaking strategy for eco-friendly and cost-effective fabrication of highly efficient perovskite solar cells. This strategy involves the usage of a high volatility co-solvent, which dilutes perovskite precursors to a lower concentration (<0.5 M) while retaining similar film quality and device performance as a high concentration (>1.4 M) solution. More than 70% of toxic waste and material cost can be reduced. Mechanistic insights reveal ultra-rapid evaporation of the co-solvent together with beneficial alteration of the precursor colloidal chemistry upon dilution with co-solvent, which in-situ studies and theoretical simulations confirm. The co-solvent tuned precursor colloidal properties also contribute to the enhancement of the stability of precursor solution, which extends its processing window thus minimizing the waste. This strategy is universally successful across different perovskite compositions, and scales from small devices to large-scale modules using industrial spin-coating, potentially easing the lab-to-fab translation of perovskite technologies.

Two hundred sixty-six films processed with flash infrared annealing were optically and structurally characterized. We determine the optimum conditions for the formation of the mixed-cations halide perovskite active phase.

Organic-inorganic perovskites have an impressive potential for the design of next generation solar cells and are currently considered for upscaling and commercialization. Currently, perovskite solar cells rely on spin-coating which is neither practical for large areas nor environmentally friendly. Indeed, one of the conventional and most effective lab-scale methods to induce perovskite crystallization, the antisolvent method, requires an amount of toxic solvent that is difficult to apply on larger surfaces. To solve this problem, an antisolvent-free and rapid thermal annealing process called flash infrared annealing (FIRA) can be used to produce highly crystalline perovskite films. The FIRA oven is composed of an array of near-infrared halogen lamps with an illumination power of 3,000 kW/m2. A hollow aluminum body enables an effective water-cooling system. The FIRA method allows the synthesis of perovskite films in less than 2 s, achieving efficiencies >20%. FIRA has a unique potential for the industry because it can be adapted to continuous processing, is antisolvent-free, and does not require lengthy, hour-long annealing steps.

We present a facile molecular-level interface engineering strategy to augment the long-term operational and thermal stability of perovskite solar cells (PSCs) by tailoring the interface between the perovskite and hole transporting layer (HTL) with a multifunctional ligand 2,5-thiophenedicarboxylic acid. The solar cells exhibited high operational stability (maximum powering point tracking at one sun illumination) with a stabilized TS80 (the time over which the device efficiency reduces to 80% after initial burn-in) of ≈5950 h at 40 °C and a stabilized power conversion efficiency (PCE) over 23%. The origin of high device stability and performance is correlated to the nano/sub-nanoscale molecular level interactions between ligand and perovskite layer, which is further corroborated by comprehensive multiscale characterization. These results provide insights into the modulation of the grain boundaries, local density of states, surface bandgap, and interfacial recombination. Chemical analysis of aged devices showed that molecular passivation suppresses interfacial ion diffusion and inhibits the photoinduced I2 release that irreversibly degrades the perovskite. The interfacial engineering strategies enabled by multifunctional ligands can expedite the path towards stable PSCs.

The optoelectronic properties, morphology, and consequently the performance of metal halide perovskite solar cells are directly related to the crystalline phases and intermediates formed during film preparation. The gas quenching method is compatible with large-area deposition, but an understanding of how this method influences these properties and performance is scarce in the literature. Here, in situ grazing incidence wide angle X-ray scattering is employed during spin coating deposition to gain insights on the formation of MAPbI(3)and Cs(x)FA(1-)(x)Pb(I0.83Br0.17)(3)perovskites, comparing the use of dimethyl sulfoxide (DMSO) and 2-methyl-n-pyrrolidone (NMP) as coordinative solvents. Intermediates formed using DMSO depend on the perovskite composition (e.g., Cs content), while for NMP the same intermediate [PbI2(NMP)] is formed independently on the composition. For MAPbI(3)and Cs(x)FA(1-)(x)Pb(I0.83Br0.17)(3)with a small amount of Cs (10% and 20%), the best efficiencies are achieved using NMP, while the use of DMSO is preferred for higher (30% and 40%) amount of Cs. The inhibition of the 2H/4H hexagonal phase when using NMP is crucial for the final performance. These findings provide a deep understanding about the formation mechanism in multication perovskites and assist the community to choose the best solvent for the desired perovskite composition aiming to perovskite-on-silicon tandem solar cells.

The use of a solution process to grow perovskite thin films allows to extend the material processability. It is known that the physicochemical properties of the perovskite material can be tuned by altering the solution precursors as well as by controlling the crystal growth of the film. This advancement necessarily implies the need for an understanding of the kinetic phenomena for the thin-film formation. Therefore, in this work we review the state of the art of perovskite hybrid crystal growth, starting from a comprehensive theoretical description towards broad experimental investigations. One part of the study focuses on rapid thermal annealing as a tool to control nucleation and crystal growth. We deduce that controlling crystal growth with high-precision photonic sintering simplifies the experimental framework required to understand perovskite crystallization. These types of synthesis methods open a new empirical parameter space. All this knowledge serves to improve the perovskite synthesis and the thin films' quality, which will result in higher device performances.

Organic-inorganic perovskites are one of the most promising photovoltaic materials for the design of next generation solar cells. The lead-based perovskite prepared with methylammonium and iodide was the first in demonstrating high power conversion efficiency, and it remains one of the most used materials today. However, perovskites prepared by mixing several halides and several cations systematically yield higher efficiencies than "pure" methylammonium lead iodide (MAPbI3) devices. In this work, we unravel the excited-state properties of a mixed-halide (iodide and bromide) and mixed-cation (methylammonium and formamidinium) perovskite. Combining time-resolved photoluminescence, transient absorption, and optical-pump-terahertz-probe experiments with density functional theory calculations, we show that the population of higher-lying excited states in the mixed material increases the lifetime of photogenerated charge carriers upon well above-bandgap excitation. We suggest that alloying different halides and different cations reduces the structural symmetry of the perovskite, which partly releases the selection rules to populate the higher-energy states upon light absorption. Our investigation thus shows that mixed halide perovskites should be considered as an electronically different material than MAPbI3, paving the way toward further materials optimization and improved power conversion efficiency of perovskite solar cells.

Flash infrared annealing (FIRA) of perovskite films enables manufacturing compact perovskite layers for photovoltaic devices. Here, a variable infrared pulse length to control crystal nucleation and growth in perovskite films is investigated. By varying the FIRA parameters, high-quality films are fabricated of fully inorganic and hybrid perovskites. Furthermore, film characterizations are analyzed for each FIRA protocol, unveiling the nature of the film growth. This demonstrates the versatility of FIRA and establishes it as a fast synthesis process, which provides detailed control over the perovskite morphology and crystallinity.

Wide band-gap perovskite solar cells have the potential for a relatively high output voltage and resilience in a degradation-inducing environment. Investigating the reasons why high voltages with adequate output power have not been realized yet is an underexplored part in perovskite research although it is of paramount interest for multijunction solar cells. One reason is interfacial carrier recombination that leads to reduced carrier lifetimes and voltage loss. To further improve the V-oc of methylammonium lead tri-bromide (MAPbBr(3)), that has a band-gap of 2.3 eV, interface passivation technique is an important strategy. Here we demonstrate two ultrathin passivation layers consisting of PCBM and PMMA, that can effectively passivate defects at the TiO2/perovskite and perovskite/spiro-OMeTAD interfaces, respectively. In addition, perovskite crystallization was investigated with the established anti-solvent method and the novel flash infrared annealing (FIRA) with and without passivation layers. These modifications significantly suppress interfacial recombination providing a pathway for improved V-OC's from 1.27 to 1.41 V using anti solvent and from 1.12 to 1.36 V using FIRA. Furthermore, we obtained more stable devices through passivation after 140 h where the device retained 70% of the initial performance value.

The analysis of the impedance spectroscopy (IS) data of perovskite solar cells (PSCs) has been challenging so far, with the low-frequency phenomena in particular yielding ambivalent results and interpretations. We tackle this problem by carrying out intensity-modulated photocurrent spectroscopy (IMPS) measurements at open-circuit (OC) conditions on CH3NH3PbBr3 cells prepared by the flash infrared annealing method with different electron-selective contacts. We identify the existence of a capacitance of the order 10(-4) F.cm(-2) that is not discernible from IS measurements, which is attributed to the accumulation of anions at the perovskite/spiro-OMeTAD interface, which also likely includes an electronic component. This interface is a dominant recombination pathway at lower voltages and can account for the large disparity in fill factors observed in PSCs. By developing detailed models for the IMPS response at both OC and short-circuit conditions, we also confirm that the arcs observed in the upper quadrant of the IMPS spectra are not related to transport times, as is commonly interpreted, but time constants results from the combination of the series resistance and capacitors within the circuit. By combining the insights from IMPS and IS measurements, we develop a more complete equivalent circuit for PSCs that can be used as a basis for further research with different perovskite materials and contact layers.

Growing large, oriented grains of perovskite often leads to efficient devices, but it is unclear if properties of the grains are responsible for the efficiency. Domains observed in SEM are commonly misidentified with crystallographic grains, but SEM images do not provide diffraction information. We study methylammoinium lead iodide (MAPbI(3)) films fabricated via flash infrared annealing (FIRA) and the conventional antisolvent (AS) method by measuring grain size and orientation using electron back-scattered diffraction (EBSD) and studying how these affect optoelectronic properties such as local photoluminescence (PL), charge carrier lifetimes, and mobilities. We observe a local enhancement and shift of the PL emission at different regions of the FIRA clusters, but we observe no effect of crystal orientation on the optoelectronic properties. Additionally, despite substantial differences in grain size between the two systems, we find similar optoelectronic properties. These findings show that optoelectronic quality is not necessarily related to the orientation and size of crystalline domains.

For successful commercialization of perovskite solar cells, straightforward solutions in terms of environmental impact and economic feasibility are still required. Flash Infrared Annealing (FIRA) is a rapid method to fabricate perovskite solar cells with efficiencies >18% on simple, planar architecture, which allows a film synthesis in only 1.2 s, faster than the previous report based in a meso architecture and all of them without the usage of antisolvent. In this work, through a comparative study with the common lab-scale method, the so-called antisolvent (AS), the main photovoltaic parameters and working mechanisms obtained from impedance spectroscopy (IS) measurements show similar device features as for FIRA. However, from the life cycle assessment (LCA) comparison study, the FIRA method has only 8% of the environmental impact and 2% of the fabrication cost of the perovskite active layer with respect to the AS for the perovskite film synthesis. These results denote that FIRA is a low-impact, cost-effective fabrication approach that can be directly adapted to perovskite planar configuration that is compatible with industrial up-scaling.