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Herein, we show how electron microscopy can provide atomic-level understanding of FAPbBr3, where electron diffraction and high-resolution imaging were combined allowing not only the characterization of the pristine material but also the identification of different intermediates upon its structural disintegration. Additionally, a minor tetragonal phase was also identified whose structure was also solved., Funding support has been received from the MCIN (RYC2018-024561-I) and DGA (E13_20R), the European Union's Horizon 2020 research and innovation programme (823717 – ESTEEM3), the NFSC (21850410448 and 21835002) and The Centre for High-resolution Electron Microscopy (CħEM), ShanghaiTech University (EM 02161943). E. J. J.-P. acknowledges MCIN/AEI/10.13039/501100011033 and European Union Next Generation EU/PRTR (PID2019-107893RB-I00 and EIN2020-112315, respectively).

Herein, we show how electron microscopy can provide atomic-level understanding of FAPbBr

13 figures, 6 tables.-- Supplementary information available., Pyrolysis of formamidinium halide salts (FAI, FABr) results in a new type of amorphous carbon nitride materials with a mass fraction of 40–50% nitrogen content. Pyrolysis temperature drives final chemical composition, morphology, optical and electrical properties of the material independently of the halide precursor and identifying triazine ring, instead of typical heptazine unit, as the main building block of this material. We elaborated a temperature dependent mechanism of formation for these materials and foresee its potential value as native passivation layer in the field of perovskite solar cells., E.J.J-P acknowledges the funding support from MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR (project grants PID2019-107893RB-I00 and EIN2020-112315, respectively). M.H. acknowledges the funding support from MCIN/AEI/10.13039/501100011033 for the Ramón y Cajal fellowship (RYC-2018-025222-I) and the project PID2019-108247RA-I00. R.A. acknowledges funding from the Spanish MICINN (project grant PID2019-104739 GB-100/AEI/10.13039/501100011033). RA also acknowledge to Government of Aragon (project DGA E13-20R (FEDER, EU)) and European Union H2020 program “ESTEEM3” (823717). A.A-C acknowledges financial support from Spanish MCIN/AEI/10.13039/501100011033 under project PID2019-104272RB-C51/AEI/10.13039/501100011033 and the Diputación General de Aragón under project T03_20R (Grupo Reconocido).

The influence of light soaking and heat stress on the degradation of indium tin oxide (ITO)/CH3NH3SnI3 and SiO2/CH3NH3SnI3 hybrid perovskite is studied. The measurements of X-ray photoelectron surv...

et al., Large datasets are now ubiquitous as technology enables higher-throughput experiments, but rarely can a research field truly benefit from the research data generated due to inconsistent formatting, undocumented storage or improper dissemination. Here we extract all the meaningful device data from peer-reviewed papers on metal-halide perovskite solar cells published so far and make them available in a database. We collect data from over 42,400 photovoltaic devices with up to 100 parameters per device. We then develop open-source and accessible procedures to analyse the data, providing examples of insights that can be gleaned from the analysis of a large dataset. The database, graphics and analysis tools are made available to the community and will continue to evolve as an open-source initiative. This approach of extensively capturing the progress of an entire field, including sorting, interactive exploration and graphical representation of the data, will be applicable to many fields in materials science, engineering and biosciences., Open access funding provided by Helmholtz-Zentrum Berlin für Materialien und Energie GmbH., The core funding of the project has been received from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 787289. We acknowledge the following sources for individual funding. Cambridge India Ramanujan Scholarship, China Scholarship Council, Deutscher Akademischer Austauschdienst (DAAD), EPSRC (grant no. EP/S009213/1), European Union’s Horizon 2020 research and innovation programme (grant no. 764787, EU Project ‘MAESTRO’), (grant no. 756962, ERC Project ‘HYPERION’), (grant no. 764047, EU Project ‘ESPResSo’ and grant no. 850937), GCRF/EPSRC SUNRISE (EP/P032591/1), German Federal Ministry for Education and Research (BMBF), HyPerFORME, NanoMatFutur (grant no. 03XP0091). PEROSEED (ZT-0024), Helmholtz Energy Materials Foundry, The Helmholtz Innovation Laboratory HySPRINT. BMBF (grant nos. 03SF0540, 03SF0557A), HyPerCells graduate school, Helmholtz Association, Helmholtz International Research School (HI-SCORE), the Erasmus programme (CDT-PV, grant no. EP/L01551X/1), the European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie grant agreement nos. 841386, 795079 and 840751), Royal Society University Research Fellowship (grant no. UF150033). SNaPSHoTs (BMBF), SPARC II, German Research Foundation (DFG, grant no. SPP2196), The National Natural Science Foundation of China (grant no. 51872014), the Recruitment Programme of Global Experts, Fundamental Research Funds for the Central Universities and the ‘111’ project (grant no. B17002), the US Department of Energy’s Office of Energy Efficiency and Renewable Energy under Solar Energy Technologies Office (SETO) agreement no. DE-EE0008551, the Colombia Scientific Programme in the framework of the call Ecosistema Cientifíco (Contract no. FP44842-218-2018), the committee for the development of research (CODI) of the Universidad de Antioquia (grant no. 2017-16000), Spanish MINECO (Severo Ochoa programme, grant no. SEV‐2015‐0522), the Swedish research council (VR, grant no. 2019-05591) and the Swedish Energy Agency (grant no. 2020-005194).

Time-correlated single photon counting has been conducted to gain further insights into the short photoluminescence lifetimes (nanosecond) of lead iodide perovskite (MAPbI3) thin films (∼100 nm). We analyze three different morphologies, compact layer, isolated island, and connected large grain films, from 14 to 300 K using a laser excitation power of 370 nJ/cm2. Lifetime fittings from the Generalized Berberan-Santos decay model range from 0.5 to 6.5 ns, pointing to quasi-direct bandgap emission despite the three different sample strains. The high energy band emission for the isolated-island morphology shows fast recombination rate centers up to 4.8 ns–1, compared to the less than 2 ns–1 for the other two morphologies, similar to that expected in a good quality single crystal of MAPbI3. Low-temperature measurements on samples reflect a huge oscillator strength in this material where the free exciton recombination dominates, explaining the fast lifetimes, the low thermal excitation, and the thermal escape obtained., This work has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie grant agreement no. 704998 (R.C.-J.). This study was also supported by the Spanish MINECO (projects TEC2014-53727-C2-1-R/2-R) and Ministry of Science and Innovation of Spain under Project STABLE (PID2019-107314RB-I00).

Carbon electrode-based perovskite solar cells (PSCs) with low-cost and long-term stability have been recognized as a competitive candidate toward future practical applications. However, energy leve...

In recent years, the major factors that determine commercialization of perovskite photovoltaic technology have been shifting from solar cell performance to stability, reproducibility, device upscaling and the prevention of lead (Pb) leakage from the module over the device service life. Here we simulate a realistic scenario in which perovskite modules with different encapsulation methods are mechanically damaged by a hail impact (modified FM 44787 standard) and quantitatively measure the Pb leakage rates under a variety of weather conditions. We demonstrate that the encapsulation method based on an epoxy resin reduces the Pb leakage rate by a factor of 375 compared with the encapsulation method based on a glass cover with an ultraviolet-cured resin at the module edges. The greater Pb leakage reduction of the epoxy resin encapsulation is associated with its optimal self-healing characteristics under the operating conditions and with its increased mechanical strength. These findings strongly suggest that perovskite photovoltaic products can be deployed with minimal Pb leakage if appropriate encapsulation is employed. Lead leakage from damaged perovskite solar cells poses a challenge to the deployment of such technology. Here, Jiang, Qiu and co-workers quantify lead leakage caused by a simulated hail impact under a number of weather conditions and show that self-healing encapsulations can effectively reduce it.

The thermal stability and decomposition products of formamidinium, a widely used organic cation in perovskite solar cell formulation, were investigated. The thermal degradation experiments of formamidinium-based perovskites and their halide precursors were carried out under helium atmosphere and vacuum at a constant heating rate of 20 degrees C min(-1). In addition, pulsed heating steps were employed under illumination/dark conditions to simulate a more realistic working temperature condition for photovoltaic devices. The identification of gas decomposition products was based on the quadrupole mass spectrometry technique. The released amounts of sym-triazine, formamidine, and hydrogen cyanide (HCN) were observed to highly depend on the temperature. For the experimental conditions used in this study, sym-triazine was obtained as the thermal product of degradation at temperatures above 95 degrees C. Below this temperature, only formamidine and HCN generation routes were observed. The energy pathways of formamidinium thermal degradation under photovoltaic working temperature conditions were further assessed by density functional theory calculations. The results indicated that formamidinium was more resilient to thermal degradation and the release of irreversible decomposition products compared to methylammonium because of a larger enthalpy and activation energy obtained for the decomposition reactions. The HCN instantaneous concentration observed during the low temperature heating tests and the estimations of the maximum release of HCN achievable per meter-square of an FA based perovskite based solar cell were compared to acute exposure guideline levels of airborne HCN concentration.

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.

We have been able to prepare two new lead halides with the formula DMAPbX3 (where DMA is dimethylammonium and X is Cl− or Br−), which display a 4H-hexagonal perovskite polytype, an unusual crystal structure in hybrid organic–inorganic perovskites. Both compounds experience a first-order phase transition, the chloride at ∼320 K and the bromide at ∼250 K, which involves two cooperative processes: an off-center shift of the lead cations and an order–disorder process of the DMA cations. Additionally, a sharp dielectric transition is associated with this structural transition in both hybrids. Both compounds are semiconductors with band gap values of 3.5 eV (X: Cl−) and 3.0 eV (X: Br−). Also, the LT-phase of the Br− compound displays a broad red light photoluminescence (PL) emission (620 nm) and PLE excitation with the maximum at a soft UV wavelength (360 nm). This broadband emission and large Stokes-shifted PL seem to be related to a self-trapped exciton mechanism. Therefore, the uncommon 4H-hexagonal perovskite is a promising crystal structure for understanding and designing new hybrid materials with broad photoluminescent emission and dielectric properties.

Nanomaterials undergoing cyclic swelling-deswelling benefit from inner void spaces that help accommodate significant volumetric changes. Such flexibility, however, typically comes at a price of reduced mechanical stability, which leads to component deterioration and, eventually, failure. Here, we identify an optimised building block for silicon-based lithium-ion battery (LIB) anodes, fabricate it with a ligand- and effluent-free cluster beam deposition method, and investigate its robustness by atomistic computer simulations. A columnar amorphous-silicon film was grown on a tantalum-nanoparticle scaffold due to its shadowing effect. PeakForce quantitative nanomechanical mapping revealed a critical change in mechanical behaviour when columns touched forming a vaulted structure. The resulting maximisation of measured elastic modulus (similar to 120GPa) is ascribed to arch action, a well-known civil engineering concept. The vaulted nanostructure displays a sealed surface resistant to deformation that results in reduced electrode-electrolyte interface and increased Coulombic efficiency. More importantly, its vertical repetition in a double-layered aqueduct-like structure improves both the capacity retention and Coulombic efficiency of the LIB. Lithiation of anodes during cycling of lithium-ion batteries generates stresses that reduce operation lifetime. Here, a composite silicon-based anode with a nanoscale vaulted architecture shows high mechanical stability and electrochemical performance in a lithium-ion battery., Communications Materials, 2 (1), ISSN:2662-4443

In this paper, the physical mechanisms responsible for optical gain in ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{Pb}\mathrm{I}}_{3}$ (MAPI) polycrystalline thin films are investigated experimentally and theoretically. Waveguide structures composed by a MAPI film embedded in between PMMA and silica layers are used as an efficient geometry to confine emitted light in MAPI films and minimize the energy threshold for amplified spontaneous emission (ASE). We show that photogenerated exciton density at the ASE threshold is as low as $(2.4\ensuremath{-}12)\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.1em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, which is below the Mott transition density reported for this material and the threshold transparency condition deduced with the free-carrier model. Such a low threshold indicates that the formation of excitons plays an important role in the generation of optical gain in MAPI films. The rate-equation model including gain is incorporated into a beam-propagation algorithm to describe waveguided spontaneous emission and ASE in MAPI films, while using the optical parameters experimentally determined in this work. This model is a useful tool to design active photonic devices based on MAPI and other metal-halide semiconductors.

The thermal stability and identification of decomposition products of formamidinium organic based precursors and hybrid perovskite materials have been investigated under inert atmosphere at constant heating rate and pulsed heating steps under illumination/dark conditions.[1] As in the previous case studied for methylammonium based precursors and perovskites, the thermogravimetry technique coupled to quadrupole mass spectrometry allows to draw interesting insights about the thermal stability of these hybrid perovskite materials allowing forecasts towards their operational stability working as light harvester material in photovoltaic devices. In this talk, we compare and review the different results obtained in four recent articles in the topic of decomposition products determination for formamidinium based perovskite paying special attention to the HCN release. We will discuss general tenets and beliefs misleading on the topic of stability of perovskite materials and finally, we will propose an operational stability test for perovskite solar cells without consensus. [1] E. J. Juarez-Perez, L. K. Ono, Y. Qi, Thermal degradation of formamidinium based lead halide perovskites into sym-triazine and hydrogen cyanide observed by coupled thermogravimetry - mass spectrometry analysis, J. Mater. Chem. A 2019, 7, 16912-16919.

Dynamic disorders, which possess a finite charge delocalization, play a critical role in the charge transport properties of high-mobility molecular organic semiconductors. The use of two-dimensional (2D) charge transport in crystalline organic semiconductors can effectively facilitate reducing the sensitivity of charge carriers to thermal energetic disorders existing in even single crystals to enhance the carrier mobility. An isotropic transfer integral among adjacent molecules enables a dimensional transition from quasi-one-dimensional to 2D for charge transport among molecules. Herein, a tuned molecular packing, especially molecular rotation, was achieved in highly crystalline organic thin films via a brush-coating method. This tuned molecular packing was favorable for approaching isotropic transfer integrals. Consequently, high-performance organic transistors with a carrier mobility up to $21.5\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and low angle dependence were obtained. This work presents a unique modulation of molecular packing at the molecular scale to enable less sensitivity of the charge transport to dynamic disorders, providing an alternative route for enhancing the electrical performance of organic electronic devices.

Besides high efficiency, the stability and reproducibility of perovskite solar cells (PSCs) are also key for their commercialization. Herein, we report a simple perovskite formation method to fabricate perovskite films with thickness over 1 μm in ambient condition on the basis of the fast gas−solid reaction of chlorine-incorporated hydrogen lead triiodide and methylamine gas. The resultant thick and smooth chlorine-incorporated perovskite films exhibit full coverage, improved crystallinity, low surface roughness and low thickness variation. The resultant PSCs achieve an average power conversion efficiency of 19.1 ± 0.4% with good reproducibility. Meanwhile, this method enables an active area efficiency of 15.3% for 5 cm × 5 cm solar modules. The un-encapsulated PSCs exhibit an excellent T80 lifetime exceeding 1600 h under continuous operation conditions in dry nitrogen environment.

A simple and inexpensive technique to synthesize and deposit Cu(II) oxide (CuO) nanostructured layers is reported herein together with electrical and optical properties characterization. The 2-step deposition procedure consists of spin-coating a Cu(II) formate solution on fluorine-doped tin oxide (FTO) conducting glass substrate followed by a heat treatment. Fluorescence spectroscopy and Fourier transform infrared spectroscopy confirmed that the organic ligand precursor is absent in the obtained film. X-ray diffraction (XRD) experiments show that only CuO films are deposited on the FTO substrate ruling out the presence of other Cu x O oxides. Scanning-electron microscopy reveals their nanostructured morphology; which agrees with crystallite size domain (L = 21 nm) estimated from XRD width peak analysis. Absorption coefficient spectra, as well as direct-gap values (E g = 1.52–1.55 eV), were obtained using optical transmittance and reflection spectroscopy. Finally, the as prepared CuO films are used as photoelectrodes in a photoelectrochemical cell with an aqueous electrolyte and short-circuit photocurrent under illumination and dark conditions is measured.

In organic field-effect transistors, the first few molecular layers at the semiconductor/dielectric interface are regarded as the active channel for charge transport; thus, great efforts have been devoted to the modification and optimization of molecular packing at such interfaces. Here, we report organic monolayers with large-area uniformity and high crystallinity deposited by an antisolvent-assisted spin-coating method acting as the templating layers between the dielectric and thermally evaporated semiconducting layers. The predeposited crystalline monolayers significantly enhance the film crystallinity of upper layers and the overall performance of transistors using these hybrid-deposited semiconducting films, showing a high carrier mobility up to 11.3 cm2 V–1 s–1. Additionally, patterned transistor arrays composed of the templating monolayers are fabricated, yielding an average mobility of 7.7 cm2 V–1 s–1. This work demonstrates a promising method for fabricating low-cost, high-performance, and large-...

Hybrid lead halide perovskites have emerged as promising active materials for photovoltaic cells. Although superb efficiencies have been achieved, it is widely recognized that long-term stability is a key challenge intimately determining the future development of perovskite-based photovoltaic technology. Herein, we present reversible and irreversible photodecomposition reactions of methylammonium lead iodide (MAPbI3). Simulated sunlight irradiation and temperature (40–80 °C) corresponding to solar cell working conditions lead to three degradation pathways: (1) CH3NH2 + HI (identified as the reversible path), (2) NH3 + CH3I (the irreversible or detrimental path), and (3) a reversible Pb(0) + I2(g) photodecomposition reaction. If only the reversible reactions (1) and (3) take place and reaction (2) can be avoided, encapsulated MAPbI3 can be regenerated during the off-illumination timeframe. Therefore, to further improve operational stability in hybrid perovskite solar cells, detailed understanding of how to mitigate photodegradation and thermal degradation processes is necessary. First, encapsulation of the device is necessary not only to avoid contact of the perovskite with ambient air, but also to prevent leakage of volatile products released from the perovskite. Second, careful selection of the organic cations in the compositional formula of the perovskite is necessary to avoid irreversible reactions. Third, selective contacts must be as chemically inert as possible toward the volatile released products. Finally, hybrid halide perovskite materials are speculated to undergo a dynamic formation and decomposition process; this can gradually decrease the crystalline grain size of the perovskite with time; therefore, efforts to deposit highly crystalline perovskites with large crystal sizes may fail to increase the long-term stability of photovoltaic devices.

Organic–inorganic halide perovskite materials (e.g., MAPbI3, FAPbI3, etc.; where MA = CH3NH3+, FA = CH(NH2)2+) have been studied intensively for photovoltaic applications. Major concerns for the commercialization of perovskite photovoltaic technology to take off include lead toxicity, long-term stability, hysteresis, and optimal bandgap. Therefore, there is still need for further exploration of alternative candidates. Elemental composition engineering of MAPbI3 and FAPbI3 has been proposed to address the above concerns. Among the best six certified power conversion efficiencies reported by National Renewable Energy Laboratory on perovskite-based solar cells, five are based on mixed perovskites (e.g., MAPbI1–xBrx, FA0.85MA0.15PbI2.55Br0.45, Cs0.1FA0.75MA0.15PbI2.49Br0.51). In this paper, we review the recent progress on the synthesis and fundamental aspects of mixed cation and halide perovskites correlating with device performance, long-term stability, and hysteresis. In the outlook, we outline the future research directions based on the reported results as well as related topics that warrant further investigation.(Some mathematical expressions are not properly displayed. Please see the attachment.)

Organo-lead-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of over 22%, and perovskite light-emitting diodes have recently achieved over 11% external quantum efficiency. To date, most research on perovskite light-emitting diodes has focused on solution-processed films. There are many advantages of a vapor-based growth process to prepare perovskites, including ease of patterning, ability to batch process, and material compatibility. We investigated an all-vapor perovskite growth process by chemical vapor deposition and demonstrated luminance up to 560 cd/m2.

This is a comment on an article in Sustainable Energy & Fuels reporting time-resolved mass spectrometry (MS) of evolved gas species during photo-induced degradation of methylammonium lead iodide perovskite (MAPbI3 ).Note:The authors of the commented article released a response to these observations on February 1, 2019. This document has been updated including new comments to their response on March 13, 2019, see page 4. For the original version of this comment, please see version 1.

Lead halide (APbX3) perovskites, in polycrystalline thin films but also perovskite nanoparticles (NPs) has demonstrated excellent performance to implement a new generation of photovoltaic and photonic devices. The structural characterization of APbX3 thin films using (scanning) transmission electron microscopy ((S)TEM) techniques can provide valuable information that can be used to understand and model their optoelectronic performance and device properties. However, since APbX3 perovskites are soft materials, their characterization using (S)TEM is challenging. Here, we study and compare the structural properties of two different metal halide APbX3 perovskite thin films: bulk CH3NH3PbI3 prepared by spin-coating of the precursors in solution and CsPbBr3 colloidal NPs synthetized and deposited by doctor blading. Both specimen preparation methods and working conditions for analysis by (S)TEM are properly optimized. We show that CH3NH3PbI3 thin films grown by a one-step method are composed of independent grains with random orientations. The growth method results in the formation of tetragonal perovskite thin films with good adherence to an underlying TiO2 layer, which is characterized by a photoluminescence (PL) emission band centered at 775 nm. The perovskite thin films based on CsPbBr3 colloidal NPs, which are used as the building blocks of the film, are preserved by the deposition process, even if small gaps are observed between adjacent NPs. The crystal structure of CsPbBr3 NPs is cubic, which is beneficial for optical properties due to its optimal band gap. The absorption and PL spectra measured in both the thin film and the colloidal solution of CsPbBr3 NPs are very similar, indicating a good homogeneity of the thin films and the absence of aggregation of NPs. However, a particular care was required to avoid long electron irradiation times during our structural studies, even at a low voltage of 80 kV, as the material was observed to decompose through Pb segregation.

Photonic applications based on halide perovskites, namely CH3NH3PbI3 (MAPbI3), have recently attracted remarkable attention due to the high efficiencies reported for photovoltaic and light emitting devices. Despite these outstanding results, there are many temperature-, laser excitation power-, and morphology-dependent phenomena that require further research to be completely understood. In this work, we have investigated in detail the nature of exciton optical transitions and recombination dynamics below and above the orthorhombic/tetragonal ('O'-/'T'-) temperature phase transition (∼150 K) depending on the material continuity (continuous-like) or discontinuity (island-like) in MAPbI3 films. At low temperatures, continuous thin films of the perovskite can exhibit strain inhomogeneities associated with the formation of different 'T'-defective domains leading to an energy spread of states over more than 200 meV. On the other hand, a single photoluminescence line peak related to the perovskite 'O'-phase (associated with the distortion of the [PbI3]- anion) is observed in the island-like sample that we attribute to strain relaxation for this morphology. Moreover, the predominantly radiative recombination dynamics of the continuous-like sample mainly originates from nongeminate electron-hole formation of excitons in the 'O'-phase and the internal dynamics with carrier trapping levels. This observation is in strong contrast to the free exciton recombination dominantly found in the island-like sample.

The use of a solid hole transport layer (HTL) was transformational for the recent perovskite solar cell (PSC) revolution in solar energy technology. Often high efficiency PSC devices employ heavily doped hole transport materials such as spiro-MeOTAD. Independent of HTL chemistry, lithium-bis-trifluoromethanesulfonyl-imide (LiTFSI) and tert-butylpyridine (TBP) are commonly used as additives in HTL formulations for PSCs. LiTFSI and TBP were originally optimized for dye-sensitized solar cells, where their roles have been extensively studied. However, in the case of PSCs, the function of TBP is not clearly understood. In this study, properties of the HTL composite deposited on flat silicon substrates were systematically measured at several length scales, e.g., macroscopically (profilometry, 4-point probe conductivity, and thermogravimetry-differential thermal analysis), microscopically, and at the nanoscale to investigate film morphology, conductivity, and dopant distribution. Microscopic distributions of spi...

An organo-metal halide perovskite is a promising material for solar cell applications, but the polycrystalline nature of perovskites can cause thin films to be non-uniform with disconnected grains. These grain boundaries make the perovskite film vulnerable to the local chemical environment, or allow unwanted direct contact of the electron transporting layer and the hole transporting layer, increasing carrier recombination. We show that post-annealing with methylamine greatly reduces impurities at perovskite grain boundaries and promotes continuity between adjacent grains. When methylamine post-annealed perovskite films are compared to thermally or solvent-annealed films, the carrier lifetime is increased by 3 times. The recombination resistance for the planar perovskite solar cells with the methylamine post-annealing treatment is increased more than 10 times, and the efficiency is increased by 43.1% and 20.0% with respect to the thermally annealed and solvent-annealed perovskite solar cells, respectively. In addition, we show that methylamine post-annealed, meso-structured perovskite solar cells exhibited a power conversion efficiency of up to 18.4%, with significantly improved stability.

M.H. is supported by the MICIU (Spain) through a Ramon y Cajal Fellowship (grant RYC-2018-025222-I).

It is comment for an article in Sustainable Energy & Fuels reporting time-resolved mass spectrometry (MS) of evolved gas species during photo-induced degradation of methylammonium lead iodide perovskite (MAPbI3 ).

Because of the rapid rise of the efficiency, perovskite solar cells are currently considered as the most promising next-generation photovoltaic technology. Much effort has been made to improve the efficiency and stability of perovskite solar cells. Here, it is demonstrated that the addition of a novel organic cation of 2-(6-bromo-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)ethan-1-ammonium iodide (2-NAM), which has strong Lewis acid and base interaction (between C=O and Pb) with perovskite, can effectively increase crystalline grain size and reduce charge carrier recombination of the double cation FA(0.83)MA(0.17)PbI(2.51)Br(0.49) perovskite film, thus boosting the efficiency from 17.1 +/- 0.8% to 18.6 +/- 0.9% for the 0.1 cm(2) cell and from 15.5 +/- 0.5% to 16.5 +/- 0.6% for the 1.0 cm(2) cell. The champion cell shows efficiencies of 20.0% and 17.6% with active areas of 0.1 and 1.0 cm(2), respectively. Moreover, the hysteresis behavior is suppressed and the stability is improved. The result provides a promising route to further elevate efficiency and stability of perovskite solar cells by the fine tuning of triple organic cations.

Semiconductor organometallic halide (CH 3 NH 3 PbX 3 , X=Cl, Br, I) perovskites (HPVK) have been emerged as a potential gain media to construct a new generation of active photonic devices. Indeed, during the last three years a significant effort has been carried out to implement HPVK-based optical amplifiers or lasers with improved quality factors. In particular, minimization of the threshold of stimulated emission has been an important concern to decrease the power consumption, and hence to enhance the performances of the device. For this purpose strategies include a suitable integration of the semiconductor in a photonic structure, or the optimization of the material. Here we propose a novel approach to develop optical amplifiers by an appropriate passivation of HPVK layers incorporated in an optical waveguide. For this purpose, geometrical parameters were firstly properly optimized to demonstrate amplification of stimulated emission with a threshold as a low as 2 nJ. In addition, the passivation of traps of the semiconductor by introducing organic additives (twisted hexaazatrinaphthylene and bisthiadiazolefused tetraazapentacenequinone) resulted in a further reduction of the threshold (down to four fold). These results provide a novel scheme to enhance the applications of perovskite active devices.

The environmental performance of four different device assembly procedures based on hybrid halide perovskite solar cell (PSC) were assessed from cradle to grave using life cycle assessment (LCA) methodology. In addition, a new environmental indicator was defined to measure the time evolution of an impact category, specifically in this case, human toxicity cancer payback time. PSCs procedures accounted for the probably three more used basic recipes for laboratory perovskite deposition: 1) spin coating of stoichiometric precursor solution, 2) spin coating of precursor solution using lead chloride precursor and 3) the two step deposition method. Also, the two most widely used substrate configurations (planar and mesoporous substrate) were considered. LCA included three realistic scenarios for the end of life: 1) residual landfill, 2) reuse and residual landfill and 3) reuse and recycling. The remaining variable parameters to assemble the device were fixed in common for all four devices, which were the major responsible of the whole PSC impact. Lead of PSCs had no significant contribution in environmental impacts. Beyond shared procedure steps, impacts generated by the twostep method and the use of mesostructured type substrate were higher. End of life scenario with reuse and recycling improved the toxicity impact categories.

Organic-inorganic lead trihalide perovskites have emerged as an outstanding photovoltaic material that demonstrated a high 17.9% conversion efficiency of sunlight to electricity in a short time. We have found a giant dielectric constant (GDC) phenomenon in these materials consisting on a low frequency dielectric constant in the dark of the order of ε0 = 1000. We also found an unprecedented behavior in which ε0 further increases under illumination or by charge injection at applied bias. We observe that ε0 increases nearly linearly with the illumination intensity up to an additional factor 1000 under 1 sun. Measurement of a variety of samples of different morphologies, compositions, and different types of contacts shows that the GDC is an intrinsic property of MAPbX3 (MA = CH3NH3(+)). We hypothesize that the large dielectric response is induced by structural fluctuations. Photoinduced carriers modify the local unit cell equilibrium and change the polarizability, assisted by the freedom of rotation of MA. The study opens a way for the understanding of a key aspect of the photovoltaic operation of high efficiency perovskite solar cells.

Organometal halide perovskite-based solar cells have recently realized large conversion efficiency over 15% showing great promise for a new large scale cost-competitive photovoltaic technology. Using impedance spectroscopy measurements we are able to separate the physical parameters of carrier transport and recombination in working devices of the two principal morphologies and compositions of perovskite solar cells, viz. compact thin films of CH3NH3PbI3–xClx and CH3NH3PbI3 infiltrated on nanostructured TiO2. The results show nearly identical spectral characteristics indicating a unique photovoltaic operating mechanism that provides long diffusion lengths (1 μm). Carrier conductivity in both devices is closely matched, so that the most significant differences in performance are attributed to recombination rates. These results highlight the central role of the CH3NH3PbX3 semiconductor absorber in carrier collection and provide a new tool for improved optimization of perovskite solar cells. We report for the first time a measurement of the diffusion length in a nanostructured perovskite solar cell. We thank the following agencies for supporting this research: GeneralitatValenciana (ISIC/2012/008) and Universitat Jaume I project 12I361.01/1. We thank SCIC from Universitat Jaume I for the help with SEM measurements.

New organoselenium( II )halidesofthetype[RSe] + X − [R = 2,6-(Me 2 NCH 2 ) 2 C 6 H 3 ;X=Cl( 2 ), Br ( 3 ), I ( 4 )] were prepared by cleavage of the Se – Se bond in R 2 Se 2 ( 1 )withSO 2 Cl 2 followed by halogen exchange when organo- selenium chloride was treated with NaBr or KI. The reaction between 2 and R ’ 2 MCl n resulted in new ionic [RSe] + [R ’ 2 MCl n +1 ] − [R ’ =2-(Me 2 NCH 2 )C 6 H 4 , n =1,M=Sb( 5 ), Bi ( 6 ); R ’ =Ph,M=Sb, n =1( 7 )or n =3( 8 )] species. All new compounds were investigated in solution by multinuclear NMR spectroscopy ( 1 H, 13 C, 77 Se, 2D experiments) and mass spectrometry. The ionic nature of 2 and the antimonates species was con fi rmed by conductivity studies. The molecular structures of [{2,6-(Me 2 NCH 2 ) 2 C 6 H 3 }Se] + Cl − · n H 2 O( 2 ·H 2 Oand 2 ·2H 2 O) and [{2,6-(Me 2 NCH 2 ) 2 C 6 H 3 }Se] + [Ph 2 SbCl 4 ] − ( 8 ), respectively, were established by single-crystal X-ray di ff raction, pointing out that the ionic nature of the se compounds is also preserved in the solid state, with both nitrogen atoms strongly trans coordinated to the selenium atom of the cation. Theoretical calculations carried out at the DFT level were exploite d to investigate the nature of the bonding in compounds 2 – 4 and the free cation [RSe] + ( 2a ). A topological analysis based on the theory of Atoms-In-Molecules (AIM) and Electron Localization Function (ELF) jointly to a Natural Bond Orbital (NBO) approach was used to shed light on the e ff ect of the nature of the halogen specie s X on the bonding within the 3c-4e N – Se – Nmoiety

Carrier diffusion length and lifetime parameters for electron transport at nanoscale semiconductor slabs have been fitted using a 1D model and the decay data extracted from transient photoemission electron microscopy. Meanwhile, a conventional photoluminescence quenching measurement needs two separate samples with an active material between blocking and quenching layers to characterize the carrier transport properties. In this work, only one few-layer monocrystalline sample of gamma-InSe containing different thicknesses of active material is used to obtain a common diffusion coefficient consistent with previously reported values for vertical carrier diffusion in layered InSe.

An upscalable perovskite film deposition method combining raster ultrasonic spray coating and chemical vapor deposition is reported. This method overcomes the coating size limitation of the existing stationary spray, single‐pass spray, and spin‐coating methods. In contrast with the spin‐coating method (>90% Pb waste), negligible Pb waste during PbI2 deposition makes this method more environmentally friendly. Outstanding film uniformity across the entire area of 5 cm × 5 cm is confirmed by both large‐area compatible characterization methods (electroluminescence and scattered light imaging) and local characterization methods (atomic force microscopy, scanning electron microscopy, photoluminescence mapping, UV–vis, and X‐ray diffraction measurements on multiple sample locations), resulting in low solar cell performance decrease upon increasing device area. With the FAPb(I0.85Br0.15)3 (FA = formamidinium) perovskite layer deposited by this method, champion solar modules show a power conversion efficiency of 14.7% on an active area of 12.0 cm2 and an outstanding shelf stability (only 3.6% relative power conversion efficiency decay after 3600 h aging). Under continuous operation (1 sun light illumination, maximum power point condition, dry N2 atmosphere with

Novel polyhedral oligomeric silsesquioxanes (POSS) or octasilses- quioxanes with carboranyl-styrene fragments attached to each corner are described. These compounds have been synthesized by olefin-metathesis reac- tions between octavinylsilsesquioxane and carboranyl-styrene compounds that possess different substituents (Ph, Me, or H). In all cases, these reactions, which were catalyzed by the Grubbs catalyst, are highly regioselective and yield exclusively the E isomers. The ex- istence of the carborane cage in the POSS structure induces a remarkable thermal stability in these compounds. After combustion at 10008C, these car- boranyl-POSS compounds exhibit a mass loss lower than 10 %. The UV/ Vis absorption data of these carboran- yl-POSS compounds shows a slight bathochromic shift with respect to the carboranyl-styrene monomers, with an absorption maximum around 262 nm. Nevertheless, important differences in the emission spectra of the carboranyl- POSS compounds with regard to their carboranyl-styrene precursors are ob- served; the phenyl-o-carborane-con- taining POSS compound exhibits the highest fluorescence intensity (FF = 44 %), whereas for the POSS com- pound bearing the methyl substituent, and for the unsubstituted o-carborane clusters, the fluorescence intensity is much lower (FF = 9 and 2 %, respec- tively). This is precisely the reverse of what occurs with the monomers, in which the unsubstituted o-carboranyl- styrene compound exhibits the highest FF, and a quenching of the fluores- cence is observed in the phenyl-o-car- boranyl-styrene compound. In addi- tion, a large red shift of around 100 nm is observed for the POSS compounds with respect to their precursors. These experimental results can only be ac- counted for by the spatial ordering in- duced by the POSS core that eases in- teractions, which otherwise would not occur. These results have been con- firmed by time-dependent density func- tional theory (TDDFT) calculations that exclude a photoinduced electron transfer (PET) process in the POSS

Efficiencies of organic–inorganic lead halide perovskite solar cells (PSCs) have significantly increased in recent years, but instability issues impede their further development and application. Previous studies reported that volatile species (for example, iodine, I2) were generated when perovskites were subjected to moisture, oxygen, light illumination, applied electric field, and thermal stress (all of which are relevant to the operation of PSCs in practical applications). Here we show that I2 vapour causes severe degradation of MAPbI3 (MA: CH3NH3+) perovskite, due to chemical chain reactions. Furthermore, I2 vapour could also induce degradation of other iodide-based perovskites, such as FAPbI3 (FA: HC(NH2)2+) and FA0.8Cs0.2PbI3. The results reveal a universal degradation factor for iodide-based perovskite by I2. As the release of I2 is nearly inevitable during practical applications, this work suggests that MAPbI3 may not be suitable for long-term stable solar cells and it is imperative to develop other types of perovskite material to achieve stable PSCs. Extensive efforts are under way to tackle the degradation issue—one of the biggest challenges for the practical application of perovskite-based solar cells. Here the authors show that CH3NH3PbI3 and several other iodine-containing perovskites are inherently unstable due to decomposition caused by self-generated I2.