Constructing tin oxides Interfacial Layer with Gradient Compositions for Efficient Perovskite/Silicon Tandem Solar Cells with Efficiency Exceeding 28

Atomic layer deposition (ALD) growth of conformal thin SnOx films on perovskite absorbers offers a promising method to improve carrier-selective contacts, enable sputter processing, and prevent humidity ingress toward high-performance tandem perovskite solar cells. However, the interaction between perovskite materials and reactive ALD precursor limits the process parameters of ALD-SnOx film and requires an additional fullerene layer. Here, it demonstrates that reducing the water dose to deposit SnOx can reduce the degradation effect upon the perovskite underlayer while increasing the water dose to promote the oxidization can improve the electrical properties. Accordingly, a SnOx buffer layer with a gradient composition structure is designed, in which the compositionally varying are achieved by gradually increasing the oxygen source during the vapor deposition from the bottom to the top layer. In addition, the gradient SnOx structure with favorable energy funnels significantly enhances carrier extraction, further minimizing its dependence on the fullerene layer. Its broad applicability for different perovskite compositions and various textured morphology is demonstrated. Notably, the design boosts the efficiencies of perovskite/silicon tandem cells (1.0 cm2) on industrially textured Czochralski (CZ) silicon to a certified efficiency of 28.0%.

Pathways of Water-Induced Lead-Halide Perovskite Surface Degradation: Insights from In Situ Atomic-Scale Analysis

While organic-inorganic hybrid perovskites are emerging as promising materials for next-generation photovoltaic applications, the origins and pathways of perovskite instability remain speculative. In particular, the degradation of perovskite surfaces by ambient water is a crucial subject for determining the long-term viability of perovskite-based solar cells. Here, we conducted surface characterization and atomic-scale analysis of the reaction mechanisms for methylammonium lead bromide (MA(CH3NH3)PbBr3) single crystals using ambient-pressure atomic force microscopy (AP-AFM) and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) in environments ranging from ultrahigh vacuum to 0.01 mbar of water vapor. MAPbBr3 single crystals, grown by a solution process, were mechanically cleaved under UHV conditions to obtain an atomically clean surface. Consecutive topography and friction force measurements in low-pressure water (pwater ≈ 10-5 mbar) revealed the formation of degraded patches, one atomic layer deep, gradually increasing their coverage until the surface was entirely covered at a water exposure of 4.7 × 104 langmuir (L). At the perimeters of these degraded patches, a higher friction coefficient was observed, along with an interstitial step height, which we attribute to a structure equivalent to that of the MA-Br terminated surface. Combined with NAP-XPS analysis, our results demonstrate that water vapor induces the dissociation of surface methylammonium ligands, eventually resulting in the depletion of the surface MA and the full coverage of hydrocarbon species after exposure to 0.01 mbar of water vapor.

Role of Surface Features on the Initial Dissolution of CH3NH3PbI3 Perovskite in Liquid Water: An Ab Initio Molecular Dynamics Study

The degradation of CH3NH3PbI3 (MAPbI3) hybrid organic inorganic perovskite (HOIP) by water has been the major issue hampering its use in commercial perovskites solar cells (PSCs), as MAPbI3 HOIP has been known to easily degrade in the presence of water. Even though there have been numerous studies investigating this phenomenon, there is still no consensus on the mechanisms of the initial stages of dissolution. Here, we attempt to consolidate differing mechanistic interpretations previously reported in the literature through the use of the first-principles constrained ab initio molecular dynamics (AIMD) to study both the energetics and mechanisms that accompany the degradation of MAPbI3 HOIP in liquid water. By comparing the dissolution free energy barrier between surface species of different surficial types, we find that the dominant dissolution mechanisms of surface species vary widely based on the specific surface features. The high sensitivity of the dissolution mechanism to surface features has contributed to the many dissolution mechanisms proposed in the literature. In contrast, the dissolution free energy barriers are mainly determined by the dissolving species rather than the type of surfaces, and the type of surfaces the ions are dissolving from is inconsequential toward the dissolution free energy barrier. However, the presence of surface defects such as vacancy sites is found to significantly lower the dissolution free energy barriers. Based on the estimated dissolution free energy barriers, we propose that the dissolution of MAPbI3 HOIP in liquid water originates from surface defect sites that propagate laterally along the surface layer of the MAPbI3 HOIP crystal.

In Situ and Operando Characterization Techniques in Stability Study of Perovskite-Based Devices

Metal halide perovskite materials have demonstrated significant potential in various optoelectronic applications, such as photovoltaics, light emitting diodes, photodetectors, and lasers. However, the stability issues of perovskite materials continue to impede their widespread use. Many studies have attempted to understand the complex degradation mechanism and dynamics of these materials. Among them, in situ and/or operando approaches have provided remarkable insights into the degradation process by enabling precise control of degradation parameters and real-time monitoring. In this review, we focus on these studies utilizing in situ and operando approaches and demonstrate how these techniques have contributed to reveal degradation details, including structural, compositional, morphological, and other changes. We explore why these two approaches are necessary in the study of perovskite degradation and how they can be achieved by upgrading the corresponding ex situ techniques. With recent stability improvements of halide perovskite using various methods (compositional engineering, surface engineering, and structural engineering), the degradation of halide perovskite materials is greatly retarded. However, these improvements may turn into new challenges during the investigation into the retarded degradation process. Therefore, we also highlight the importance of enhancing the sensitivity and probing range of current in situ and operando approaches to address this issue. Finally, we identify the challenges and future directions of in situ and operando approaches in the stability research of halide perovskites. We believe that the advancement of in situ and operando techniques will be crucial in supporting the journey toward enhanced perovskite stability.

Unveiling facet-dependent degradation and facet engineering for stable perovskite solar cells

A myriad of studies and strategies have already been devoted to improving the stability of perovskite films; however, the role of the different perovskite crystal facets in stability is still unknown. Here, we reveal the underlying mechanisms of facet-dependent degradation of formamidinium lead iodide (FAPbI₃) films. We show that the (100) facet is substantially more vulnerable to moisture-induced degradation than the (111) facet. With combined experimental and theoretical studies, the degradation mechanisms are revealed; a strong water adhesion following an elongated lead-iodine (Pb-I) bond distance is observed, which leads to a δ-phase transition on the (100) facet. Through engineering, a higher surface fraction of the (111) facet can be achieved, and the (111)-dominated crystalline FAPbI₃ films show exceptional stability against moisture. Our findings elucidate unknown facet-dependent degradation mechanisms and kinetics.

Environmental and health risks of perovskite solar modules: Case for better test standards and risk mitigation solutions

Perovskite solar cells (PSCs) promise high efficiencies and low manufacturing costs. Most formulations, however, contain lead, which raises health and environmental concerns. In this review, we use a risk assessment approach to identify and evaluate the technology risks to the environment and human health. We analyze the risks by following the technology from production to transportation to installation to disposal and examine existing environmental and safety regulations in each context. We review published data from leaching and air emissions testing and highlight gaps in current knowledge and a need for more standardization. Methods to avoid lead release through introduction of absorbing materials or use of alternative PSC formulations are reviewed. We conclude with the recommendation to develop recycling programs for PSCs and further standardized testing to understand risks related to leaching and fires.

Atomic layer deposition of PbCl2, PbBr2 and mixed lead halide (Cl, Br, I) PbXnY2-n thin films

Atomic layer deposition offers outstanding film uniformity and conformality on substrates with high aspect ratio features. These qualities are essential for mixed-halide perovskite films applied in tandem solar cells, transistors and light-emitting diodes. The optical and electronic properties of mixed-halide perovskites can be adjusted by adjusting the ratios of different halides. So far ALD is only capable of depositing iodine-based halide perovskites whereas other halide processes are lacking. We describe six new low temperature (≤100 °C) ALD processes for PbCl₂ and PbBr₂ that are crucial steps for the deposition of mixed-halide perovskites with ALD. Lead bis[bis(trimethylsilyl)amide]-GaCl₃ and -TiBr₄ processes yield the purest, crystalline, uniform and conformal films of PbCl₂ and PbBr₂ respectively. We show that these two processes in combination with a PbI₂ process from the literature deposit mixed lead halide films. The four less optimal processes revealed that reaction by-products in lead halide deposition processes may cause film etching or incorporate themselves into the film.

Role of Alkali Cations in Stabilizing Mixed-Cation Perovskites to Thermal Stress and Moisture Conditions

Perovskite solar cells (PSCs) based on organic-inorganic hybrid perovskites containing a small fraction of substituted alkali-metal cations have shown remarkable performance and stability. However, the role of these cations is unclear. The thermal- and moisture-induced degradation of FA_1-xCs_xPbI₃ and (FA_1-xCs_x)_1-yRb_yPbI₃ (where FA represents formamidinium, x, y = 0.1, 0.05) is investigated using in situ photoelectron spectroscopy (PES). Both compositions exhibit superior moisture stability compared with methylammonium lead iodide under 9 mbar of water vapor. Ga Kα hard X-ray PES is used to investigate the composition of the perovskites at depths up to 45 nm into the surface. This allows more accurate quantification of the alkali-metal distribution than is possible using conventional X-ray PES. The addition of RbI results in a fairly homogeneous distribution of both Cs⁺ and Rb⁺ in the surface layers (in contrast to surface Cs depletion seen in its absence), together with a marked reduction in surface iodide vacancies. Overall, RbI is found to play a critical role in increasing the thermal stability of FA_1-xCs_xPbI₃ by providing a source of I^- that fills iodine vacancy sites in the perovskite lattice, while Rb⁺ is not substantially incorporated into the perovskite. We suggest that the concomitant increase in ion migration barriers in the surface layers is key to improved PSC performance and long-lasting stability.

The Progress of Additive Engineering for CH3NH3PbI3 Photo-Active Layer in the Context of Perovskite Solar Cells

Methylammonium lead triiodide (CH3NH3PbI3/MAPbI3) is the most intensively explored perovskite light-absorbing material for hybrid organic–inorganic perovskite photovoltaics due to its unique optoelectronic properties and advantages. This includes tunable bandgap, a higher absorption coefficient than conventional materials used in photovoltaics, ease of manufacturing due to solution processability, and low fabrication costs. In addition, the MAPbI3 absorber layer provides one of the highest open-circuit voltages (Voc), low Voc loss/deficit, and low exciton binding energy, resulting in better charge transport with decent charge carrier mobilities and long diffusion lengths of charge carriers, making it a suitable candidate for photovoltaic applications. Unfortunately, MAPbI3 suffers from poor photochemical stability, which is the main problem to commercialize MAPbI3-based perovskite solar cells (PSCs). However, researchers frequently adopt additive engineering to overcome the issue of poor stability. Therefore, in this review, we have classified additives as organic and inorganic additives. Organic additives are subclassified based on functional groups associated with N/O/S donor atoms; whereas, inorganic additives are subcategorized as metals and non-metal halide salts. Further, we discussed their role and mechanism in terms of improving the performance and stability of MAPbI3-based PSCs. In addition, we scrutinized the additive influence on the morphology and optoelectronic properties to gain a deeper understanding of the crosslinking mechanism into the MAPbI3 framework. Our review aims to help the research community, by providing a glance of the advancement in additive engineering for the MAPbI3 light-absorbing layer, so that new additives can be designed and experimented with to overcome stability challenges. This, in turn, might pave the way for wide scale commercial use.

E. coli@UiO-67 composites as a recyclable adsorbent for bisphenol A removal

E. coli@UiO-67 composites were obtained using an effective and simple self-assembly method. The composites showed unique properties as a remarkable and recyclable adsorbent for the efficient removal of bisphenol A (BPA) from water with a high adsorption capacity (402.930 mg g^-1). The increase in pore size is a key factor why E. coli@UiO-67 composites maintained high capacity. The reason might be due to that the composites with large pore sizes and defects could effectively improve mass transport and active molecular metal sites. The adsorption of BPA is a chemisorption process due to the Zr-OH groups in UiO-67 exhibit affinity toward BPA molecules, π-π interaction, and electrostatic attraction. The adsorption efficiency remained at 82.5% after 15 cycles without any remarkable changes in the PXRD patterns of E. coli@UiO-67. Moreover, the use of microorganism-loading MOFs could reduce the cost to at least 50% and minimize secondary pollution through nanoscale MOFs usage reduction. The developed composites have advantages, including low-cost, high adsorption capacity, easy to be separated and regenerated from aqueous solution, a large number of cycles, short adsorption equilibrium time, and stability, showing excellent application prospects. The presented strategy would be a potentially promising way to produce novel MOFs-based adsorbents with high-performance to control environmental pollution from wastewater.

Photoemission Studies on the Environmental Stability of Thermal Evaporated MAPbI3 Thin Films and MAPbBr3 Single Crystals

Hybrid organic inorganic perovskites have been considered as a potential candidate for the next generational solar cell due to their outstanding optoelectronic properties and rapid development in recent years. However, the biggest challenge to prevent them from massive commercial use is their long-term stability. Photoemission spectroscopy has been widely used to investigate properties of the perovskites, which provide critical insights to better understand the degradation mechanisms. In this article, we review mainly our photoemission studies on the degradation processes of perovskite thin films and single crystals with different environmental factors, such as gases, water, and light by monitoring changes of chemical composition and electronic structure. These studies on the effects by different environmental parameters are discussed for the understanding of the stability issues and the possible solutions.

X-ray stability and degradation mechanism of lead halide perovskites and lead halides

Lead halide perovskites have become a leading material in the field of emerging photovoltaics and optoelectronics. Significant progress has been achieved in improving the intrinsic properties and environmental stability of these materials. However, the stability of lead halide perovskites to ionising radiation has not been widely investigated. In this study, we investigated the radiolysis of lead halide perovskites with organic and inorganic cations under X-ray irradiation using synchrotron based hard X-ray photoelectron spectroscopy. We found that fully inorganic perovskites are significantly more stable than those containing organic cations. In general, the degradation occurs through two different, but not mutually exclusive, pathways/mechanisms. One pathway is induced by radiolysis of the lead halide cage into halide salts, halogen gas and metallic lead and appears to be catalysed by defects in the perovskite. The other pathway is induced by the radiolysis of the organic cation which leads to formation of organic degradation products and the collapse of the perovskite structure. In the case of Cs0.17FA0.83PbI3, these reactions result in products with a lead to halide ratio of 1 : 2 and no formation of metallic lead. The radiolysis of the organic cation was shown to be a first order reaction with regards to the FA+ concentration and proportional to the X-ray flux density with a radiolysis rate constant of 1.6 × 10-18 cm2 per photon at 3 keV or 3.3 cm2 mJ-1. These results provide valuable insight for the use of lead halide perovskite based devices in high radiation environments, such as in space environments and X-ray detectors, as well as for investigations of lead halide perovskites using X-ray based techniques.

Ambient Pressure X-ray Photoelectron Spectroscopy Investigation of Thermally Stable Halide Perovskite Solar Cells via Post-Treatment

Long-term thermal stability is one limiting factor that impedes the commercialization of the perovskite solar cell. Inspired by our prior results from machine learning, we discover that coating a thin layer of 4,4'-dibromotriphenylamine (DBTPA) on top of a CH₃NH₃PbI₃ layer can improve the stability of resultant solar cells. The passivated devices kept 96% of the original power conversion efficiency for 1000 h at 85 °C in a N₂ atmosphere without encapsulation. Near-ambient pressure X-ray photoelectron spectroscopy (XPS) was employed to investigate the evolution of the composition and evaluate thermal and moisture stability by in situ studies. A comparison between pristine MAPbI₃ films and DBTPA-treated films shows that the DBTPA treatment suppresses the escape of iodide and methylamine up to 150 °C under 5 mbar humidity. Furthermore, we have used attenuated total reflection Fourier transform infrared and XPS to probe the interactions between DBTPA and MAPbI₃ surfaces. The results prove that DBTPA coordinates with the perovskite by Lewis acid-base and cation-π interaction. Compared with the 19.9% efficiency of the pristine sample, the champion efficiency of the passivated sample reaches 20.6%. Our results reveal DBTPA as a new post-treating molecule that leads not only to the improvement of the photovoltaic efficiency but also thermal and moisture stability.

Reducing Detrimental Defects for High-Performance Metal Halide Perovskite Solar Cells

In several photovoltaic (PV) technologies, the presence of electronic defects within the semiconductor band gap limit the efficiency, reproducibility, as well as lifetime. Metal halide perovskites (MHPs) have drawn great attention because of their excellent photovoltaic properties that can be achieved even without a very strict film-growth control processing. Much has been done theoretically in describing the different point defects in MHPs. Herein, we discuss the experimental challenges in thoroughly characterizing the defects in MHPs such as, experimental assignment of the type of defects, defects densities, and the energy positions within the band gap induced by these defects. The second topic of this Review is passivation strategies. Based on a literature survey, the different types of defects that are important to consider and need to be minimized are examined. A complete fundamental understanding of defect nature in MHPs is needed to further improve their optoelectronic functionalities.

Compositional and Morphological Changes in Water-Induced Early-Stage Degradation in Lead Halide Perovskites

With tremendous improvements in lead halide perovskite-based optoelectronic devices ranging from photovoltaics to light-emitting diodes, the instability problem stands as the primary challenge in their development. Among all factors, water is considered as one of the major culprits to the degradation of halide perovskite materials. For example, CH3NH3PbI3 (MAPbI3) and CH(NH2)2PbI3 (FAPbI3) decompose into PbI2 in days under ambient conditions. However, the intermediate changes of this degradation process are still not fully understood, especially the changes in early stage. Here we perform an in-situ investigation of the early-stage MAPbI3 and FAPbI3 degradation under high water vapor pressure. By probing the surface and bulk of perovskite samples using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and XRD, our findings clearly show that PbI2 formation surprisingly initiates below the top surface or at grain boundaries, thus offering no protection as a water-blocking layer on surface or grain boundaries to slow down the degradation process. Meanwhile, significant morphological changes are observed in both samples after water vapor exposure. In comparison, the integrity of MAPbI3 film degrades much faster than the FAPbI3 film against water vapor. Pinholes and large voids are found in MAPbI3 film while only small number of pinholes can be found in FAPbI3 film. However, the FAPbI3 film suffers from its phase instability, showing a fast α-to-δ phase transition. Our results highlight the importance of the compositional and morphological changes in the early stage degradation in perovskite materials.

Stability of Hybrid Organic-Inorganic Perovskite CH3NH3PbBr3 Nanocrystals under Co-Stresses of UV Light Illumination and Temperature

Hybrid organic–inorganic metal halide perovskite nanocrystals (NCs) are among the candidates for color conversion materials in displays, especially in NC-based micro-light-emitting diode (micro-LED) displays. However, these NCs are still lacking long-term stability, which has hindered their large-scale applications. We mimic the working conditions, which include ultraviolet light illumination at 323 K and three different types of atmosphere (N₂, vacuum, and air), respectively, to investigate the stability of CH₃NH₃PbBr₃ NCs embedded in the polyvinylidene fluoride matrix. X-ray diffraction results indicate the generation of NH₄Pb₂Br₅, which is produced from the encapsulated CH₃NH₃PbBr₃ NCs in all three atmospheres, and the decomposition generates a large amount of accompanying interface defects at the surface area of NCs, resulting in the significant decrease of the photoluminescence (PL) intensity. This work highlights the stability-related mechanism of CH₃NH₃PbBr₃ NCs under combined external stresses that mimic operating conditions. In addition, this work also suggests a new method for conducting aging tests and contributes to developing effective routes towards higher stability of perovskite NCs.

Degradation Mechanism and Relative Stability of Methylammonium Halide Based Perovskites Analyzed on the Basis of Acid-Base Theory

The correct identification of all gases released during hybrid perovskite degradation is of great significance to develop strategies to extend the lifespan of any device based on this semiconductor. CH₃X (X = Br/I) is a released degradation gas/low boiling point liquid arising from methylammonium (MA⁺) based perovskites, which has been largely overlooked in the literature focusing on stability of perovskite solar cells. Herein, we present an unambiguous identification of CH₃I release using microwave (rotational) spectroscopy. An experimental back-reaction test demonstrates that the well-known CH₃NH₂/HX degradation route may not be the ultimate degradation pathway of MAPbX₃ in thermodynamic closed systems. Meanwhile, the CH₃X/NH₃ route cannot back-react selectively to MAX formation as occurred for the former back-reaction. Metadynamics calculations uncover the X halide effect on energy barriers for both degradation reactions showing a better stability of Br based perovskite ascribed to two aspects: (i) lower Brönsted-Lowry acidity of HBr compared to HI and (ii) higher nucleophilic character of CH₃NH₂ compared to NH₃. The latter property makes CH₃NH₂ molecules stay preferentially attached on the electrophilic perovskite surface (Pb²⁺) during the dynamic simulation instead of being detached as observed for the NH₃ molecule.

The crucial role of density functional nonlocality and on-axis CH3NH3 rotation induced I2 formation in hybrid organic-inorganic CH3NH3PbI3 cubic perovskite

Effects of electronic nonlocality in density functional theory study of structural and energetic properties of a pseudocubic CH₃NH₃PbI₃ are investigated by considering coherent rotation around C–N axis of a CH₃NH₃ cation. A number of truly non-local and semi-local exchange correlation density functionals are examined by comparing calculated structural parameters with experimental results. The vdW-DF-cx which takes into account the non-local van der Waals correlation and consistent exchange shows the best overall performance for density functional theory study of this system. Remarkable distinctions between results from vdW-DF-cx and those from PBEsol exchange correlation functionals are observed and indicate the need of including the non-local interaction in the study of this system, especially its dynamical properties. The obtained rotational barriers are 18.56 meV/formula and 27.71 meV/formula which correspond to rotational frequencies of 3.71 THz and 2.60 THz for vdW-DF-cx and PBEsol calculations, respectively. Interestingly, the maximally localised Wannier function analysis shows the hydrogen bonding assisted covalent character of two iodide anions at a moderate rotational angle which can lead to I₂ formation and then material degradation.

Dynamically Disordered Lattice in a Layered Pb-I-SCN Perovskite Thin Film Probed by Two-Dimensional Infrared Spectroscopy

The dynamically flexible lattices in lead halide perovskites may play important roles in extending carrier recombination lifetime in 3D perovskite solar-cell absorbers and in exciton self-trapping in 2D perovskite white-light phosphors. Two-dimensional infrared (2D IR) spectroscopy was applied to study a recently reported Pb-I-SCN layered perovskite. The Pb-I-SCN perovskite was spin-coated on a SiO₂ surface as a thin film, with a thickness of ∼100 nm, where the S¹²CN^- anions were isotopically diluted with the ratio of S¹²CN:S¹³CN = 5:95 to avoid vibrational coupling and excitation transfer between adjacent SCN^- anions. The ¹²CN stretch mode of the minor S¹²CN^- component was the principal vibrational probe that reported on the structural evolution through 2D IR spectroscopy. Spectral diffusion was observed with a time constant of 4.1 ± 0.3 ps. Spectral diffusion arises from small structural changes that result in sampling of frequencies within the distribution of frequencies comprising the inhomogeneously broadened infrared absorption band. These transitions among discrete local structures are distinct from oscillatory phonon motions of the lattice. To accurately evaluate the structural dynamics through measurement of spectral diffusion, the vibrational coupling between adjacent SCN^- anions had to be carefully treated. Although the inorganic layers of typical 2D perovskites are structurally isolated from each other, the 2D IR data demonstrated that the layers of the Pb-I-SCN perovskite are vibrationally coupled. When both S¹²CN^- and S¹³CN^- were pumped simultaneously, cross-peaks between S¹²CN and S¹³CN vibrations and an oscillating 2D band shape of the S¹²CN^- vibration were observed. Both observables demonstrate vibrational coupling between the closest SCN^- anions, which reside in different inorganic layers. The thin films and the isotopic dilution produced exceedingly small vibrational echo signal fields; measurements were made possible using the near-Brewster's angle reflection pump-probe geometry.

Thermodynamics and the Intrinsic Stability of Lead Halide Perovskites CH3NH3PbX3

The role of thermodynamics in assessing the intrinsic instability of the CH₃NH₃PbX₃ perovskites (X = Cl,Br,I) is outlined on the basis of the available experimental information. Possible decomposition/degradation pathways driven by the inherent instability of the material are considered. The decomposition to precursors CH₃NH₃X(s) and PbX₂( s) is first analyzed, pointing out the importance of both the enthalpic and the entropic factor, the latter playing a stabilizing role making the stability higher than often asserted. For CH₃NH₃PbI₃, the disagreement between the available calorimetric results makes the stability prediction uncertain. Subsequently, the gas-releasing decomposition paths are discussed, with emphasis on the discrepant results presently available, probably reflecting the predominance of thermodynamic or kinetic control. The competition between the formation of NH₃(g) + CH₃X(g), CH₃NH₂(g) + HX(g) or CH₃NH₃X(g) is analyzed, in comparison with the thermal decomposition of methylammonium halides. In view of the scarce and inconclusive thermodynamic studies to-date available, the need for further experimental data is emphasized.

Prospects for Mitigating Intrinsic Organic Decomposition in Methylammonium Lead Triiodide Perovskite

Organometallic lead halide perovskites seem to be on the threshold of becoming viable commercial photovoltaics; however, further improvements to the stability of these materials must be made before they can compete with existing photovoltaic technologies. Of the organometallic lead halide perovskites used in photovoltaics, methylammonium lead triiodide perovskite (MAPI) is perhaps the most studied, and understanding how MAPI degrades is crucial for developing strategies to improve stability. We discuss the experimental evidence behind several possible routes for MAPI to degrade into PbI₂ and various organics, and how the decomposition path of MAPI may strongly depend on substrate, precursors, intrinsic organic defects, and morphology. Exploring the conditions required for MAPI to degrade according to a particular pathway is important not only from a fundamental materials chemistry perspective, but also for understanding intrinsic instability in MAPI-based photovoltaics and to develop strategies to improve stability.