Combining Perovskites and Quantum Dots: Synthesis, Characterization, and Applications in Solar Cells, LEDs, and Photodetectors

Metal halide perovskites having high defect tolerance, high absorption characteristics, and high carrier mobility demonstrate great promise as potential light harvesters in photovoltaics and optoelectronics and have experienced an unprecedented development since their occurrence in 2009. Semiconductor quantum dots (QDs), on the other hand, have also been proved to be very flexible toward shape, dimension, bandgap, and optical properties for constructing optoelectronic devices. Of late, a strategic combination of both materials has demonstrated extraordinary promise in photovoltaic applications and optoelectronic devices. Combining QDs and perovskites has proved to be quite an effective strategy toward the formation of pinhole-free and more stable perovskite crystals along with tunability of other properties. To boost this exciting research field, it is imperative to summarize the work done so far in recent years to provide an intriguing insight. This review is a critical account of the advanced strategy toward combining these two fascinating materials, including their different synthetic approaches regarding heteroepitaxial growth of perovskite crystals on QDs, carrier dynamics at the interface and potential application in the field of solar cells, light emitting diodes, and photodetectors.S.R. acknowledges Marie Skłodowska-Curie Actions (Project H2020-MSCA-IF-2019-897030). This work was supported by MCIN/AEI/ 10.13039/501100011033, JCCM (FEDER) and the European Union (EU) through projects PID2020-116519RB-I00 and SBPLY/19/180501/000212, respectively; and by the European Research Council (ERC) via Consolidator Grant (724424-No-LIMIT). P.P. acknowledges the support from National Science Centre (Poland) through project No. 2017/26/D/ST3/00910

Hexaazatriphenylene-Based Hydrogen-Bonded Organic Framework with Permanent Porosity and Single-Crystallinity

Hydrogen-bonded organic frameworks (HOFs) have drawn unprecedented interest because of their high crystallinity as well as facile process for construction, deconstruction, and reassembly arising from reversible bond formation-dissociation. However, structural fragility and low stability frequently prevent formation of robust HOFs with permanent porosity. Here, we report that hexakis(4-carboxyphenyl)-hexaazatriphenylene (CPHAT) forms three dimensionally networked H-bonded framework CPHAT-1. Interestingly, the activated framework CPHAT-1 a retains not only permanent porosity but single-crystallinity, enabling precise structural characterization and property evaluation on a single crystal. Moreover, CPHAT-1 a retains its framework up to 339 °C or in hot water and in acidic aqueous solution. These results clearly show that even a simple H-bonding motif can be applied for the construction of robust HOFs, which creates a pathway to establish a new class of porous organic frameworks. We also characterize its uptake of gases and I2, in addition to a detailed photophysical study (spectroscopy and dynamics of proton and charge transfers) of its unit in solution, and of its single crystal under fluorescence microscopy, in which we observed a marked strong anistropy and narrow distribution. The results bring new findings to the area of HOFs and their possible applications in science and technology.This is the accepted version of the following article: Hisaki I., Ikenaka N., Gomez E., et al. Hexaazatriphenylene-Based Hydrogen-Bonded Organic Framework with Permanent Porosity and Single-Crystallinity. Chemistry - A European Journal 23, 11611 (2017), which has been published in final form at https://doi.org/10.1002/chem.201701893. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html

Femto- to Millisecond Time-Resolved Photodynamics of a Double-Functionalized Push–Pull Organic Linker: Potential Candidate for Optoelectronically Active MOFs

© 2020 by the authors.The design of improved organic linkers for the further engineering of smarter metal–organic framework (MOF) materials has become a paramount task for a wide number of material scientists. In this report, a luminescent double-functionalized push–pull (electron donor–acceptor) archetype organic molecule, dimethyl 4-amino-8-cyanonaphthalene-2,6-dicarboxylate (Me2CANADC), has been synthesized and characterized. The optical steady-state properties of Me2CANADC are strongly influenced by the surrounding environment as a direct consequence of its strong charge transfer (CT) character. The relaxation from its first electronically excited singlet state follows a double pathway: (1) on one side deactivating from its local excited (LE) state in the sub-picosecond or picosecond time domain, and (2) on the other side undergoing an ultrafast intramolecular charge transfer (ICT) reaction that is slowing down in viscous solvents. The deactivation to the ground state of these species with CT character is the origin of the Me2CANADC luminescence, and they present solvent-dependent lifetime values ranging from 8 to 18 ns. The slow photodynamics of Me2CANADC unveils the coexistence of a non-emissive triplet excited state and the formation of a long-lived charge separated state (2 µs). These observations highlight the promising optical properties of Me2CANADC linker, opening a window for the design of new functional MOFs with huge potential to be applied in the fields of luminescent sensing and optoelectronics.This work was supported by the MINECO (Spain) through projects MAT-2017-8653-R and MAT2017-82288-C2-2-P. L. Duplouy-Armani thanks the university of Lille and Moblilex /France) for the mobility grant to the UCLM (Spain).Peer reviewe

Docking Strategy To Construct Thermostable, Single-Crystalline, Hydrogen-Bonded Organic Framework with High Surface Area

Enhancing thermal and chemical durability and increasing surface area are two main directions for the construction and improvement of the performance of porous hydrogen-bonded organic frameworks (HOFs). Herein, a hexaazatriphenylene (HAT) derivative that possesses six carboxyaryl groups serves as a suitable building block for the systematic construction of thermally and chemically durable HOFs with high surface area through shape-fitted docking between the HAT cores and interpenetrated three-dimensional network. A HAT derivative with carboxybiphenyl groups forms a stable single-crystalline porous HOF that displays protic solvent durability, even in concentrated HCl, heat resistance up to 305 °C, and a high Brunauer–Emmett–Teller surface area [SA(BET)] of 1288 m2 g−1. A single crystal of this HOF displays anisotropic fluorescence, which suggests that it would be applicable to polarized emitters based on robust functional porous materials.This is the accepted version of the following article: Hisaki I., Suzuki Y., Gomez E., et al. Docking Strategy To Construct Thermostable, Single-Crystalline, Hydrogen-Bonded Organic Framework with High Surface Area. Angewandte Chemie - International Edition 57, 12650 (2018), which has been published in final form at https://doi.org/10.1002/anie.201805472. This article may be used for non-commercialpurposes in accordance with the Wiley Self-ArchivingPolicy [https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html

Perovskite-Quantum Dots Interface: Deciphering its Ultrafast Charge Carrier Dynamics

Understanding electron and hole (e,h) transport at semiconductor interfaces is paramount to developing efficientoptoelectronic devices. Halide perovskite/semiconductor quantum dots (QDs) have emerged as smart hybridsystems with a huge potential for light emission and energy conversion. However, the dynamics of generated e-hpairs are not fully understood. Ultrafast UV–VIS transient absorption and THz spectroscopies have enabled us tounravel the processes of the e-h recombination within a hybrid film of methylammonium lead triiodide (MAPbI3)interacting with different amount of PbS/CdS core/shell QDs. To accurately analyze the complex behavior, weapplied a new model for e-h events in this hybrid material. The results obtained with sample having a highconcentration of QDs (7.3 mass percentage) indicate: (i) a large population (92%) of the photogenerated chargecarriers are affected by QDs presence. The main part of these carriers (85% of the total) in perovskite domaindiffuse towards QDs, where they transfer to the interface (electrons) and QD´s valence bands (holes) with rateconstants of 1.2 × 1010s−1and 4.6 × 1010s−1, respectively. 7% of these affected charged entities are excitonsin the perovskite domain in close vicinity of the interface, and show a recombination rate constant of 3.7 × 1010s−1.(ii) The carriers not affected by QDs presence (8%) recombine through known perovskite deactivationchannels. Lowering the QDs mass percentage to 0.24 causes a decrease of electron and hole effective transfer rateconstants, and disappearance of excitons. These results provide clues to improve the performance of perovskite/QD based device

Guest entrapment in metal-organic nanosheets for quantifiably tuneable luminescence

Luminescent metal-organic frameworks (LMOFs) are promising materials for nanophotonic applications due to their tuneable structure and programmability. Yet, the 3D nature of LMOFs creates challenges for stability, optical transparency, and device integration. Metal-organic nanosheets (MONs) potentially overcome these limitations by combining the benefits of metal-organic frameworks (MOFs) with an atomically thin morphology of large planar dimensions. Herein, the bottom-up synthesis of few-layer thin ZIF-7-III MONs via facile low-energy salt-templating is reported. Employing guest@MOF design, the fluorophores Rhodamine B and Fluorescein are intercalated into ZIF-7 nanosheets (Z7-NS) to form light emissive systems exhibiting intense and highly photostable fluorescence. Aggregation and Förster resonance energy transfer, enabled by the MON framework, are revealed as the mechanisms behind fluorescence. By varying guest concentration, these mechanisms provide predictable quantified control over emission chromaticity of a dual-guest Z7-NS material and the definition of an “emission chromaticity fingerprint” – a unique subset of the visible spectrum that a material can emit by fluorescence

Unraveling Competitive Electron and Energy-Transfer Events at the Interfaces of a 2D MOF and Nile Red Composites: Effect of the Length and Structure of the Linker

[EN] The distribution and interactions of organic molecules adsorbed on the surface of materials play important roles in many catalytic and photonic processes. Here, we show that the length and chemical structure of the linker in new Al-ITQ metal-organic frameworks (MOFs) are fundamental for the dynamics of the dye Nile Red (NR) adsorbed on its surface. For the studied composites using A1-ITQ-4-ethylbenzoic acid (EB), Al-ITQ-4-aminobenzoic acid (AB), and Al-ITQ : EB exposed to the aniline (AN) or N,N-dimethylani-line (DMA) atmospheres, we observed a very fast (similar to 1.2 ps) intramolecular charge-transfer reaction in adsorbed NR molecules. For NR@Al-ITQEB, where the linker has a shorter aliphatic chain (two carbons), the dye molecules present a homoenergy-transfer (ET) process, which is faster (similar to 90 ps) than in the previously reported NR@Al-ITQ-4-heptylbenzoic acid composite with longer aliphatic chain (seven carbons, similar to 220 ps). The more polar environment created by the Al-oxide nodes in Al-ITQ-EB surface around the NR populations strongly favors the ET event. When the linker structure contains phenyl amine moieties, the resulting NR@Al-ITQ-AB composites show different and rich photodynamics, in which a fast electron transfer reaction from the MOF aniline moiety to the adsorbed NR occurs in similar to 17 ps, inhibiting the ET process between the dye molecules near the MOF surface. This process also was confirmed in Al-ITQ-EB MOF exposed to AN and DMA gas atmospheres, as well as NR in pure aniline. The obtained results demonstrate how modifications in the length and structure of the organic linker in this MOF change the interface interactions and outcome of the photoinduced processes in the composites. Our findings on dye-MOF interface photobehavior are relevant to the design of new materials in which the interface plays a key role in their performance in the fields of catalysis and photonics.This work was supported by MINECO through projects MAT2014-57646-P, MAT2017-86532-R, and MAT2017-82288-C2-1-P. J.M.M. thanks the predoctoral fellowship from the Severo Ochoa program for support (SEV-2016-0683), and E.C.-M thanks the MINECO for the FPI fellowship (BES-2015-071495). We thank Dr. John Spencer Baskin for reading the manuscript.Caballero-Mancebo, E.; Moreno-Rodríguez, JM.; Cohen, B.; Díaz Morales, UM.; Corma Canós, A.; Douhal, A. (2018). Unraveling Competitive Electron and Energy-Transfer Events at the Interfaces of a 2D MOF and Nile Red Composites: Effect of the Length and Structure of the Linker. ACS Applied Materials & Interfaces. 10(38):32885-32894. https://doi.org/10.1021/acsami.8b12188S3288532894103

Acid Responsive Hydrogen-Bonded Organic Frameworks

A porous hydrogen-bonded organic framework (HOF) responsive to acid was constructed from a hexaazatrinaphthylene derivative with carboxyphenyl groups (CPHATN). Precise structures of both 1,2,4-trichlorobenzene solvate [CPHATN-1(TCB)] and activated HOF with permanent porosity (CPHATN-1a) were successfully determined by single-crystalline X-ray diffraction analysis. Permanent porosity of CPHATN-1a was evaluated by gas sorption experiments at low temperature. CPHATN-1a also shows significant thermal stability up to 633 K. Its crystals exhibit a rich photochemistry thanks to intramolecular charge-transfer and interunit proton-transfer reactions. Femtosecond (fs) experiments on crystals demonstrate that these events occur in ≤200 fs and 1.2 ps, respectively. Moreover, single-crystal fluorescence microscopy reveals a shift of the emission spectra most probably as a result of defects and a high anisotropic behavior, reflecting an ordered crystalline structure with a preferential orientation of the molecular dipole moments. Remarkably, CPHATN-1a, as a result of the protonation of pyradyl nitrogen atoms embedded in its π-conjugated core, shows reversible vapor acid-induced color changes from yellow to reddish-brown, which can be also followed by an ON/OFF of its emission. To the best of our knowledge, this is the first HOF that exhibits acid-responsive color changes. The present work provides new findings for developing stimuli responsive HOFs.Hisaki I., Suzuki Y., Gomez E., et al. Acid Responsive Hydrogen-Bonded Organic Frameworks. Journal of the American Chemical Society. 141(5), 2111-2121, (2019), 6 February 2019; © 2019 American Chemical Society. https://doi.org/10.1021/jacs.8b12124

Deciphering the Role of Quantum Dots Size in the Ultrafast Charge Carrier Dynamics at the Perovskite-Quantum Dots Interface

Understanding the behaviour of electrons and holes (e, h) diffusion and transfer at the interfaces of photoexcited hybrid materials at different densities of photoexcited charge carriers is paramount to the development of efficient optoelectronic devices. Nanocomposites formed by methylammonium lead iodide perovskite (MAPbI3) and semiconductor colloidal quantum dots (QDs)are among these hybrid materials under intensive studies. However, the reciprocal influence of the components in the composite material on the temporal evolution of the photoinduced charge carriers is still poorly explored. This study explores the ultrafast temporal behaviour of the photoexcited charge carriers in MAPbI3/PbS QDs films, letting a special attention to the role of the PbS QD size. Armed with fs-time-resolved UV-VIS transient absorption and terahertz techniques, we unravel the effect of different sizes of PbS QDs, embedded in perovskite (PS) host matrix, on the processes of e and h diffusion, transfer to the QDs phase and recombination. While the decays are dominated by e and h transition from PS to QDs, the increase in the size of QDs results in an acceleration of the charge carriers transition processes represented by the total transition rate constants of electrons (ke) and holes (kh). The total ke and kh values change form 0.1and 1 (109 s-1) to 4.5and 22 (109 s-1), respectively. We extract the rate constants of their diffusions (kediff = 2.2 × 1010s-1 and khdiff = 1.1 × 1010 s-1) and transfers to the interfaces (ket = 0.1 to 1.6 × 1010 s-1 and kht = 0.1 to 0.8 × 1010 s-1). Furthermore, the analysis of spectral behavior of PS and PS/QDs upon pumping with different fs-laser fluences indicate the presence and photoformation of excitonic states. The acceleration of such processes decreases the contribution of undesirable charge carriers trapping and non-radiative recombination within PS