We study the influence of electrical biasing on the modification of the chemical composition and electrical performance of perovskite solar cells (PSCs) by coupling electrochemical impedance spectroscopy (EIS) and scanning transmission X-ray microscopy (STXM) techniques. EIS reveals the formation of charge accumulation at the interfaces and changes in the resistive and capacitive properties. STXM study on PSCs after applying a strong electric field for a long biasing time indicates the breakdown of methylammonium (MA+) cation, promoting iodide ions to migrate and create defects at the interface. This complementary EIS and STXM study allows the suggestion of a degradation mechanism that includes the migration of iodide ions that leads to interface defects and subsequent degradation of solar cell performance. In addition, we study the evolution of the performance of PSCs under air. We observe an increased hysteresis index on current-voltage curves and fill factor reduction of the perovskite solar cells with aging in air. EIS measurements show the formation of a capacitive layer resulting from the accumulation of iodide ions through modification of the mobile ion concentration and ion mobility.

We report the straightforward synthesis of Si-containing PAHs. The impact of pi-extension and exocyclic modifications on both the optical and redox properties is investigated using a joint experimental/theoretical approach. By taking advantage of the solid-state luminescence of these derivatives, electroluminescent devices are prepared. Such preliminary optoelectronic results highlight that these heteroatom-containing PAHs are promising building blocks for organic electronics.

Defects usually behave as imperfections in materials that significantly degrade their performance. However, the unusual optoelectronic performance in metal halide perovskites in the presence of defects opens the way for strain and optoelectronic properties tailoring with ion irradiation. Defects and strain engineering is performed in triple‐cation mixed halide perovskites using proton irradiation at 1 MeV and different fluences. At intermediate fluence, the initial polycrystalline film compressive strain (−0.15%) can be released, improving exciton lifetimes from about 500 ns to ≈1 µs. In contrast, high irradiation fluence is shown to restore compressive strain leading to sample degradation, with lower lifetime values (≈200 ns). Also, the phase segregation occurring under light illumination between bromine‐rich and iodine‐rich regions is shown to be defects‐mediated as the segregation rate increases by a factor of four for high proton irradiation fluence. The irradiation defects are revealed with low‐temperature photoluminescence (PL) through bound exciton radiative recombination mechanisms. The PL temperature dependence gives some insight into electron–phonon coupling mechanism and their modification with ion irradiation.

Metal-halide perovskites are complex materials with outstanding optoelectronic properties. Thus it is of interest to analyze these materials by using every available research tool. Synchrotron tools have played an important role in fundamental and applied research for decades. Many synchrotron-based hard X-ray tools are already providing effective feedback to the perovskite solar cell (PSC) research community. With several fourth-generation light sources up and running or under development, this contribution will continue to impact every aspect of scientific advancement including PSC research. Arguably, the contribution of soft X-rays in PSC research is relatively limited. In view of the developments in the synchrotron world and the fact that a multimethod approach, combining laboratory-based techniques as well as synchrotron-based techniques, is necessary to provide constructive feedback to the PSC community we present here a collection of arguments and procedures with the aim of highlighting the use of soft X-ray scanning transmission X-ray microscopy (STXM). Some aspects of these arguments are elaborated with STXM investigation of perovskite material formamidinium-methylammonium lead iodide (FA1−xMAxPbI3).

We report the synthesis and characterization of benzophospholes oxides featuring ethoxy substituent on the P atom and electro-donating amino groups on the lateral phenyl groups. The optical and redox properties of these compounds are studied experimentally and computationally (TD-DFT). In particular, we show how the nature of the donor allows to fine tune the Internal Charge Transfer (ICT) and, thus, the optical properties. Considering the intense fluorescence in the solid-state, the favorable redox and thermal properties, compounds were inserted in multilayered Organic Light Emitting Devices. All compounds display high efficiency and one compound even reaches 5% of external quantum efficiency (EQE), which represents the theoretical limit of EQE of purely fluorescent emitters. These results highlight the potential of this novel family of fluorophores to develop optoelectronic/photonic devices of next generation.

Organic–inorganic metal halide perovskites (MHPs) have recently been receiving a lot of attention due to their newfound application in optoelectronic devices, including perovskite solar cells (PSCs) which have reached power conversion efficiencies as high as 25.5%. However, the fundamental mechanisms in PSCs, including the correlation of degradation with the excellent optoelectrical properties of the perovskite absorbers, are poorly understood. In this paper, we have explored synchrotron-based soft X-ray characterization as an effective technique for the compositional analysis of MHP thin films. Most synchrotron-based studies used for investigating MHPs so far are based on hard X-rays (5–10 keV) which include various absorption edges (Pb L-edge, I L-edge, Br K-edge, etc.) but are not suited for the analysis of the organic component in these materials. In order to be sensitive to a maximum number of elements, we have employed soft X-ray-based scanning transmission X-ray microscopy (STXM) as a spectro-microscopy technique for the characterization of MHPs. We examined its sensitivity to iodine and organic components, aging, or oxidation by-products in MHPs to make sure that our suggested method is suitable for studying MHPs. Furthermore, methylammonium triiodide with different deposition ratios of PbI 2 and CH 3 NH 3 I (MAI), and different thicknesses, were characterized for chemical inhomogeneity at the nanoscale by STXM. Through these measurements, we demonstrate that STXM is very sensitive to chemical composition and homogeneity in MHPs. Thus, we highlight the utility of STXM for an in-depth analysis of physical and chemical phenomena in PSCs.

Nowadays, phosphorescent organic light-emitting diodes (PhOLEDs) is a widespread technology, in which all the high-performance devices are constructed on a stack of different organic layers called multi-layer devices (ML-PhOLEDs). Thanks to these functional layers, the injection, the transport, and the recombination of holes and electrons in the emissive layer (EML) are significantly improved, allowing to reach high performances. In this technology, the ideal devices are the single-layer PhOLEDs (SL-PhOLEDs), with a very simple stack only constituted by the electrodes and the EML. These devices are simple, very easy to fabricate, and can hence significantly decrease their costs. Nevertheless, removing the functional layers of an OLED drastically decreases the performances and there is, so far, only a few examples of high-performance SL-PhOLEDs. Thus, in SL-PhOLEDs, the role of the functional layer should be performed by the EML, which should allow an excellent injection, transport, and recombination of holes and electrons. In this work, thanks to a rational molecular design of the EML, we report a green-emitting SL-PhOLED, displaying a very high external quantum efficiency of 22.7%. The EML of this device is constructed on the barely studied Ir(ppy)2acac phosphor and a high efficiency host material possessing a Donor-spiro-Acceptor design. This performance is, to the best of our knowledge, the highest reported to date for SL-PhOLEDs (all colors considered). Through a structure/property/device performance relationship study combining morphological (AFM), photophysical (time-resolved spectroscopy) and charge transport studies, we show that the EML presents all the required characteristics such as smooth surface, quick radiative deactivation, and ambipolarity. In addition, the comparison with Ir(ppy)3, the most famous green emitter used in PhOLEDs, highlights the high potential of Ir(ppy)2acac. The impact of the phosphorescent emitter on the ambipolarity of the charge transport is particularly evidenced.

In this paper, we present the development of OLEDs using organophosphorus derivatives as emitters. In this study, we were able to show that the structural variations carried out on phospholes, phosphinines and phosphepines (functionalization of the phosphorus atom, nature of the substituents) make it possible to modulate the emission wavelengths and, thus, the emission colour of the diodes. Using this concept, we were able to develop TADF and chiral organophosphorus emitters and hybrids emitting at different wavelengths which can be used for the development of OLEDs. The diode structures used are simple and provide high external quantum yields.

Fluorescent nanohybrids, based on π‐extended hydroxyoxophosphole ligands grafted onto ZnO nanoparticles, are designed and studied. The restriction of the intramolecular motions of the organic fluorophore, through either aggregates’ formation in solution or processing into thin films, forms highly emissive materials due to a strong aggregation induced emission effect. Theoretical calculations and XPS analyses were performed to analyze the interactions between the organic and inorganic counterparts. Preliminary results on the use of these nanohybrids as solution‐processed emissive layers in organic light emitting diodes (OLEDs) illustrate their potential for lighting applications.

We report the substitution of λ5-phosphinines (2,6-dicarbonitrile diphenyl-1-λ5-phosphinine) with an amino group. The impact of these modifications on both the optical and redox properties is investigated using a joint experimental/theoretical approach. In particular, we show that the choice of the donor diphenylamino group dramatically impacts the nature of the charge transfer. The use of di(methoxyphenyl)amine redshifts the optical properties and allows thermally activated delayed fluorescence in the solid state. Finally, we demonstrated that λ5-phosphinines with an amino group can be used as active emitters in an electroluminescent device.

We report the straightforward synthesis of Si-containing PAHs. The impact of pi-extension and exocyclic modifications on both the optical and redox properties is investigated using a joint experimental/theoretical approach. By taking advantage of the solid-state luminescence of these derivatives, electroluminescent devices are prepared. Such preliminary optoelectronic results highlight that these heteroatom-containing PAHs are promising building blocks for organic electronics.

Fluorescent organic–inorganic nanohybrids based on π-extended hydroxyoxophosphole emitters grafted onto ZnO nanocrystals, have been introduced as an efficient way to control the spatial arrangement of the organic emitters within a host material.

In-situ study of the variation of the chemical composition of triple-cation mixed halide perovskites Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 under visible light illumination performed by Fast Scanning Nano Hard X-ray Fluorescence Imaging revealed the migration and irreversible phase separation of halide ions into micro-meter sized clusters.

We describe the investigation of metal halide perovskite layers, particularly CH3NH3PbI3 used in photovoltaic applications, by soft X-ray scanning transmission X-ray microscopy (STXM). Relevant reference spectra were used to fit the experimental data using singular value decomposition. The distribution of key elements Pb, I, and O was determined throughout the layer stack of two samples prepared by wet process. One sample was chosen to undergo electrical biasing. Spectral data shows the ability of STXM to provide relevant chemical information for these samples. We found the results to be in good agreement with the sample history, both regarding the deposition sequence and the degradation of the perovskite material.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. TLM versus temperature investigation of Ag and Au direct contacts with MAPI and 3CP halide perovskites G Chau, M. Kim, Bernard Geffroy, Denis Mencaraglia

The lateral CC-π-extension of perylene diimides ( PDI s) to coronene diimides ( CDI s) leads to undesired effects such as the decrease of the absorption and a hypsochromic shift. This could be overcome by lateral BN-annulation of PDI s to form superior BNCDIs .

Readily accessible and functionalized ESIPT dyes with high fluorescence quantum yield in solution, including water, and in crystalline state are presented.