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For self-catalyzed nanowires (NWs), reports on how the catalytic droplet initiates successful NW growth are still lacking, making it difficult to control the yield and often accompanying a high density of clusters. Here, we have performed a systematic study on this issue, which reveals that the effective V/III ratio at the initial growth stage is a critical factor that governs the NW growth yield. To initiate NW growth, the ratio should be high enough to allow the nucleation to extend to the entire contact area between the droplet and substrate, which can elevate the droplet off of the substrate, but it should not be too high in order to keep the droplet. This study also reveals that the cluster growth between NWs is also initiated from large droplets. This study provides a new angle from the growth condition to explain the cluster formation mechanism, which can guide high-yield NW growth.

Mixed-dimensional van der Waals heterostructures are promising for research and technological advances in photonics and optoelectronics. Here we report vapor-liquid-solid (VLS) method -based van der Waals epitaxy of one-dimensional InP nanowires (NWs) directly on two-dimensional MoS2. With optimized growth parameters (V/III ratio, flow rates of precursors, and growth temperature), we successfully grow high-quality InP NWs on MoS2. The density and vertical yield of NWs on MoS2 are significantly high. Due to the unique properties of both materials, we observe strong linear and nonlinear optical responses from the NW/MoS2 heterostructures. Intriguingly, in addition to strong second and third harmonic responses, the mixed-dimensional heterostructures show odd-order high harmonic generation up to seventh order. Our findings can open new possibilities for advancing attosecond physics on a new platform of mixed-dimensional heterostructures.

ispartof: ADVANCED ENERGY MATERIALS status: Published online

Defective and perfect sites naturally exist within electronic semiconductors, and considerable efforts to reduce defects to improve the performance of electronic devices, especially in hybrid organic-inorganic perovskites (ABX(3)), are undertaken. Herein, foldable hole-transporting materials (HTMs) are developed, and they extend the wavefunctions of A-site cations of perovskite, which, as hybridized electronic states, link the trap states (defective site) and valence band edge (perfect site) between the naturally defective and perfect sites of the perovskite surface, finally converting the discrete trap states of the perovskite as the continuous valence band to reduce trap recombination. Tailoring the foldability of the HTMs tunes the wavefunctions between defective and perfect surface sites, allowing the power conversion efficiency of a small cell to reach 23.22% and that of a mini-module (6.5 x 7 cm, active area = 30.24 cm(2)) to reach as high as 21.71% with a fill factor of 81%, the highest value reported for non-spiro-OMeTAD-based perovskite solar modules.

Post-polymerisation functionalisation provides a facile and efficient way for the introduction of functional groups on the backbone of conjugated polymers. Using post-polymerisation functionalisation approaches, the polymer chain length is usually not affected, meaning that the resulting polymers only differ in their attached functional groups or side chains, which makes them particularly interesting for investigating the influence of the different groups on the polymer properties. For such functionalisations, highly efficient and selective reactions are needed to avoid the formation of complex mixtures or permanent defects in the polymer backbone. A variety of suitable synthetic approaches and reactions that fulfil these criteria have been identified and reported. In this review, a thorough overview is given of the post-polymerisation functionalisations reported to date, with the methods grouped based on the type of reaction used: cycloaddition, oxidation/reduction, nucleophilic aromatic substitution, or halogenation and subsequent cross-coupling reaction. Instead of modifications on the aliphatic side chains of the conjugated polymers, we focus on modifications directly on the conjugated backbones, as these have the most pronounced effect on the optical and electronic properties. Some of the discussed materials have been used in applications, ranging from solar cells to bioelectronics. By providing an overview of this versatile and expanding field for the first time, we showcase post-polymerisation functionalisation as an exciting pathway for the creation of new conjugated materials for a range of applications.

Semiconducting nanomaterials have been widely explored in diverse optoelectronic applications. Colloidal lead halide perovskite nanocrystals (NCs) have recently been an excellent addition to the field of nanomaterials, promising an enticing building block in the field of light emission. In addition to the notable optoelectronic properties of perovskites, the colloidal NCs exhibit unique size-dependent optical properties due to the quantum size effect, which makes them highly attractive for light-emitting diodes (LEDs). In the past few years, perovskite-based LEDs (PeLEDs) have demonstrated a meteoritic rise in their external quantum efficiency (EQE) values, reaching over 20% so far. Among various halide perovskite compositions, FAPbBr3 and its variants remain one of the most interesting and sought-after compounds for green light emission. This review focuses on recent progress in the design and synthesis protocols of colloidal FAPbBr3 NCs and the emerging concepts in tailoring their surface chemistry. The structural and physicochemical features of lead halide perovskites along with a comprehensive discussion on their defect-tolerant properties are briefly outlined. Later, the prevalent synthesis, ligand, and compositional engineering strategies to boost the stability and photoluminescence quantum yield (PLQY) of FAPbBr3 NCs are extensively discussed. Finally, the fundamental concepts and recent progress on FAPbBr3-based LEDs, followed by a discussion of the challenges and prospects that are on the table for this enticing class of perovskites, are reviewed. ispartof: JOURNAL OF MATERIALS CHEMISTRY C vol:10 issue:37 pages:13437-13461 ispartof: location:England status: published

Large-scale patterning for vapor-liquid-solid growth of III-V nanowires is a challenge given the required feature size for patterning (45 to 60 nm holes). In fact, arrays are traditionally manufactured using electron-beam lithography,for which processing times increase greatly when expanding the exposure area. In order to bring nanowire arrays one step closer to the wafer-scale we take a different approach and replace patterned nanoscale holes with Si nanopillar arrays. The method is compatible with photolithography methods such as phase-shift lithography or deep ultraviolet (DUV) stepper lithography. We provide clear evidence on the advantage of using nanopillars as opposed to nanoscale holes both for the control on the growth mechanisms and for the scalability. We identify the engineering of the contact angle as the key parameter to optimize the yield. In particular, we demonstrate how nanopillar oxidation is key to stabilize the Ga catalyst droplet and engineer the contact angle. We demonstrate how the position of the triple phase line at the SiO2/Si as opposed to the SiO2/vacuum interface is central for a successful growth. We compare our experiments with simulations performed in surface evolver (TM) and observe a strong correlation. Large-scale arrays using phase-shift lithography result in a maximum local vertical yield of 67% and a global chip-scale yield of 40%. We believe that, through a greater control over key processing steps typically achieved in a semiconductor fab it is possible to push this yield to 90+% and open perspectives for deterministic nanowire phase engineering at the wafer-scale.

Double perovskites are materials exhibiting excellent properties for a variety of optical and electrical applications. In this paper, we characterize the structural, electronic, optical, electrical and scintillation properties of two variants of lead-bismuth halide double perovskite, with the general chemical composition of Cs4PbBi2X12 (X = Br, I). Density functional theory calculations reveal that the Br- and I-variants have direct and indirect bandgaps, respectively. The Cs4PbBi2X12 perovskites also show a broad emission down to near infrared, suggesting the presence of self trapped excitons. Photoluminescence time-resolved measurements show a very fast decay time with average decay times of 4.1 ns and 0.39 ns, for the Br- and I-variant, respectively. Photodetectors fabricated with the Cs4PbBi2X12 perovskites show clear rectification under bias, and a moderate response to illumination. Due to the presence of very heavy atoms and density of the material, the Cs4PbBi2X12 perovskites are strong X-ray absorbers with attenuation lengths comparable to Gd2O2S, a standard X-ray phosphor. The Cs4PbBi2X12 perovskites also show strong scintillation at cryogenic temperatures below 30 K, but thermal quenching severely reduces the light yield at room temperature. Although the performances of both crystals for photodetectors and scintillators are still low in comparison with some other perovskites, they are still a very promising materials due to their short absorption length and high theoretical maximum light yield, and their optoelectronic properties could be significantly improved by ion doping. Ministry of Education (MOE) The authors acknowledge financial supports from the Ministry of Education (Singapore), under its AcRF Tier 2 grant (MOE-T2EP50121-0012), the MERLION Program, and Thales-CINTRA Funding.

The EU crystalline silicon (c-Si) PV manufacturing industry has faced strong foreign competition in the last decade. To strive in this competitive environment and differentiate itself from the competition, the EU c-Si PV manufacturing industry needs to (1) focus on highly performing c-Si PV technologies, (2) include sustainability by design, and (3) develop differentiated PV module designs for a broad range of PV applications to tap into rapidly growing existing and new markets. This is precisely the aim of the 3.5 years long H2020 funded HighLite project, which started in October 2019 under the work program LC-SC3-RES-15-2019: Increase the competitiveness of the EU PV manufacturing industry. To achieve this goal, the HighLite project focuses on bringing two advanced PV module designs and the related manufacturing solutions to higher technology readiness levels (TRL). The first module design aims to combine the benefits of n-type silicon heterojunction (SHJ) cells (high efficiency and bifaciality potential, improved sustainability, rapidly growing supply chain in the EU) with the ones of shingle assembly (higher packing density, improved modularity, and excellent aesthetics). The second module design is based on the assembly of low-cost industrial interdigitated back-contact (IBC) cells cut in half or smaller, which is interesting to improve module efficiencies and increase modularity (key for application in buildings, vehicles, etc.). This contribution provides an overview of the key results achieved so far by the HighLite project partners and discusses their relevance to help raise the EU PV industries' competitiveness. We report on promising high-efficiency industrial cell results (24.1% SHJ cell with a shingle layout and 23.9% IBC cell with passivated contacts), novel approaches for high-throughput laser cutting and edge re-passivation, module designs for BAPV, BIPV, and VIPV applications passing extended testing, and first 1-year outdoor monitoring results compared with benchmark products. This project has received funding from the European Union's Horizon 2020 Programme for research, technological development, and demonstration under Grant Agreement no. 857793.

The black perovskite phase of CsPbI3 is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI2-based interfacial microstructure into otherwise-unstable CsPbI3 perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI3 perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI3 perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches.

Sustainable water oxidation requires low-cost, stable, and efficient redox couples, photosensitizers, and catalysts. Here, we introduce the in situ self-assembly of metal-atom-free organic-based semiconductive structures on the surface of carbon supports. The resulting TTF/TTF•+@carbon junction (TTF = tetrathiafulvalene) acts as an all-in-one highly stable redox-shuttle/photosensitizer/molecular-catalyst triad for the visible-light-driven water oxidation reaction (WOR) at neutral pH, eliminating the need for metallic or organometallic catalysts and sacrificial electron acceptors. A water/butyronitrile emulsion was used to physically separate the photoproducts of the WOR, H+ and TTF, allowing the extraction and subsequent reduction of protons in water, and the in situ electrochemical oxidation of TTF to TTF•+ on carbon in butyronitrile by constant anode potential electrolysis. During 100 h, no decomposition of TTF was observed and O2 was generated from the emulsion while H2 was constantly produced in the aqueous phase. This work opens new perspectives for a new generation of metal-atom-free, low-cost, redox-driven water-splitting strategies.

III–V compound nanowires have electrical and optical properties suitable for a wide range of applications, including photovoltaics and photodetectors. Furthermore, their elastic nature allows the use of strain engineering to enhance their performance. Here we have investigated the effect of mechanical strain on the photocurrent and the electrical properties of single GaAs nanowires with radial p-i-n junctions, using a nanoprobing setup. A uniaxial tensile strain of 3% resulted in an increase in photocurrent by more than a factor of 4 during NIR illumination. This effect is attributed to a decrease of 0.2 eV in nanowire bandgap energy, revealed by analysis of the current–voltage characteristics as a function of strain. This analysis also shows how other properties are affected by the strain, including the nanowire resistance. Furthermore, electron-beam-induced current maps show that the charge collection efficiency within the nanowire is unaffected by strain measured up to 0.9%.

Funder: Cambridge Trust, Funder: National Research Foundation Singapore, Funder: Alexander von Humboldt-Stiftung, Funder: China Scholarship Council, In this paper, the ability of three selected machine learning neural and baseline models in predicting the power conversion efficiency (PCE) of organic photovoltaics (OPVs) using molecular structure information as an input is assessed. The bidirectional long short-term memory (gFSI/BiLSTM), attentive fingerprints (attentive FP), and simple graph neural networks (simple GNN) as well as baseline support vector regression (SVR), random forests (RF), and high-dimensional model representation (HDMR) methods are trained to both the large and computational Harvard clean energy project database (CEPDB) and the much smaller experimental Harvard organic photovoltaic 15 dataset (HOPV15). It was found that the neural-based models generally performed better on the computational dataset with the attentive FP model reaching a state-of-the-art performance with the test set mean squared error of 0.071. The experimental dataset proved much harder to fit, with all of the models exhibiting a rather poor performance. Contrary to the computational dataset, the baseline models were found to perform better than the neural models. To improve the ability of machine learning models to predict PCEs for OPVs, either better computational results that correlate well with experiments or more experimental data at well-controlled conditions are likely required.

The wound environment is a breeding ground for pathogens, and traditional wound dressing materials lack antibacterial properties. In this work, we aimed to develop PVA/chitosan (P/C)-based wound dressing scaffolds with anti-infective properties using Cu2ZnSnS4 quantum dots (CZTS QDs) to prevent infections in the wound. CZTS quantum dots were prepared by a simple hydrothermal process and characterized using appropriate techniques such as TEM, XRD, FTIR spectrum, and UV-Vis absorption spectroscopy. CZTS QDs were subsequently loaded at different concentrations onto PVA/chitosan membranes (0, 1.6, 2.5 and 3.3% w/w, based on the total polymer quantity). The chemical structure, contact angle and mechanical properties of the membranes were analyzed, and their antimicrobial activities and cell viability were also investigated. The cytocompatibility of the membranes and cell morphology was investigated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and SEM. Based on studies on the interactions between membranes and cells, it was determined that incorporation of CZTS QDs into the membrane did not cause toxicity. To the best of our knowledge, this is the first report on loading CZTS QDs into membranes for tissue engineering applications, and the overall findings suggest that CZTS QDs-integrated membranes might have potentially appealing uses as antimicrobial films for wound healing., Tarsus University Scientific Research Projects Coordination Department; [MF.22.003], AcknowledgementsThe authors thank the Tarsus University Scientific Research Projects Coordination Department (Project no: MF.22.003) for the supports.

For many years, fullerene derivatives have been the main n-type material of organic electronics and optoelectronics. Recently, fullerene derivatives functionalized with ethylene glycol (EG) side chains have been showing important properties such as enhanced dielectric constants, facile doping and enhanced self-assembly capabilities. Here, we have prepared field-effect transistors using a series of these fullerene derivatives equipped with EG side chains of different lengths. Transport data show the beneficial effect of increasing the EG side chain. In order to understand the material properties, full structural determination of these fullerene derivatives has been achieved by coupling the X-ray data with molecular dynamics (MD) simulations. The increase in transport properties is paired with the formation of extended layered structures, efficient molecular packing and an increase in the crystallite alignment. The layer-like structure is composed of conducting layers, containing of closely packed C60 balls approaching the inter-distance of 1 nm, that are separated by well-defined EG layers, where the EG chains are rather splayed with the chain direction almost perpendicular to the layer normal. Such a layered structure appears highly ordered and highly aligned with the C60 planes oriented parallel to the substrate in the thin film configuration. The order inside the thin film increases with the EG chain length, allowing the systems to achieve mobilities as high as 0.053 cm2 V−1 s−1. Our work elucidates the structure of these interesting semiconducting organic molecules and shows that the synergistic use of X-ray structural analysis and MD simulations is a powerful tool to identify the structure of thin organic films for optoelectronic applications., The synergistic use of X-ray scattering and molecular dynamics simulations reveals the structure–property relationships of [60]fullerene derivatives with oligoethylene–glycol side chains.

Perovskite/silicon tandem solar cells are emerging as a high-efficiency and prospectively cost-effective solar technology with great promise for deployment at the utility scale. However, despite the remarkable performance progress reported lately, assuring sufficient device stability-particularly of the perovskite top cell-remains a challenge on the path to practical impact. In this work, we analyze the outdoor performance of encapsulated bifacial perovskite/silicon tandems, by carrying out field-testing in Saudi Arabia. Over a six month experiment, we find that the open circuit voltage retains its initial value, whereas the fill factor degrades, which is found to have two causes. A first degradation mechanism is linked with ion migration in the perovskite and is largely reversible overnight, though it does induce hysteretic behavior over time. A second, irreversible, mechanism is caused by corrosion of the silver metal top contact with the formation of silver iodide. These findings provide directions for the design of new and more stable perovskite/silicon tandems

Organic-inorganic lead halide perovskite (CH3NH3PbI3) solar cells have surpassed 25% power conversion efficiency, being ready for industrial-scale production of cheap photovoltaic (PV) panels. In this action, the major hurdle is its lead content, which in case of device failure, could be washed into the soil, entering the food chain. Since there is a zero tolerance on lead in the human organism, this health hazard is a critical obstacle for commercialization. Here, we propose a solution to this problem by incorporating phosphate salts (e.g., (NH4)(2)HPO4) in PV and other perovskite-based optoelectronic devices in various architectures. Phosphate salts do not react with CH3NH3PbI3 and do not alter its advantageous optoelectronic properties, but in a wet environment, they react immediately with lead, forming a highly insoluble compound, precluding this way the spread of lead into the environment. It is expected that this study will stimulate research, enabling lead halide perovskite solar cells to reach a similar environmental risk category as the commercially available, nonwater-soluble heavy metal-containing CdTe and gallium diselenide technologies.

Ethynylene-bridged perylene diimides (PDIs) with different sized silane groups have been synthesized as a steric blocking group to prevent the formation of non-radiative trap sites, for example, strong H-aggregates and other dimers or excimers. Excited singlet-state exciton dynamics were investigated by time-resolved photoluminescence and ultrafast pump-probe transient absorption spectroscopy. The spectra of the excimer or dimer aggregates formed by the PDIs at high concentrations were also determined. Although the photophysical properties of the bare and shielded PDIs are identical at micromolar concentrations, more shielded PDI2 and PDI3 exhibited resistance to aggregation, retaining higher photoluminescence quantum yield even at 10 mM concentration and in neat films. The PDIs also exhibited high photostability (1 h of continuous excitation), as well as electrochemical stability (multiple cycles with cyclic voltammetry). Prevention of dimer/aggregate formation in this manner will extend the uses of PDIs to a variety of high concentration photonics and optoelectronic applications, such as organic light-emitting diodes, organic photovoltaics, and luminescent solar concentrators., Scientific and Technological Research Council of Turkey (TUBITAK) BIDEB-2214-A [1059B141800476]; TUBITAK [119F031]; HyperOLED project from the European Unions's Horizon 2020 Research and Innovation Program [732013], E.A. thanks The Scientific and Technological Research Council of Turkey (TUBITAK) BIDEB-2214-A (Appl. #1059B141800476) who supported this research financially. for time-resolved PL and ultrafast pump-probe TAS. E.A. and C.V. also thank the project support funds of TUBITAK (grant #119F031) for financial support of the synthesis, structural, electrochemical, and optical characterizations of perylene derivatives. A.D. and A.P.M. were supported by the HyperOLED project from the European Unions's Horizon 2020 Research and Innovation Program under grant agreement number 732013.

Indirect absorption extended below the direct transition edge and increase in carrier lifetime derived from Rashba spin–orbit coupling may advance theoptoelectronicapplications of metalhalideperovskites. Spin-orbit coupling in halide perovskites is due to the presence of heavy elements in their structure. However, when these materials lack an inversion symmetry, for example by the application of strain, spin–orbit coupling becomes odd in the electron’s momentum giving rise to a splitting in the electronic energy bands. Here we report on the observation of a large Rashba splitting of 117 meV at room temperature, as predicted by relativistic first-principles calculations, in halide perovskitesingle crystalsthrough a facile compositional engineering approach. Partial substitution oforganic cationsbyrubidiumin single crystals induces significant indirect absorption and dual peakphotoluminescenceas a result of a large Rashba splitting. We measured circularly polarized photoluminescence and magneto-photoluminescence in perovskite films printed by single crystals as well as magneto-electroluminescence and magneto-photocurrent in spin-LEDs based on perovskite single crystals. They indicated significant spin-momentum locking due to the large Rashba effect. A hybrid perovskite single crystalphotodetectorachieved record figures of merit, including detectivity of more than 1.3 × 1018Jones which represents a three orders of magnitude improvement compared to the to date record. These findings show that facile compositional engineering of perovskite single crystals holds great promise for further advancing the optoelectronic properties of existing materials.

Surface and bulk molecular modulators are the key to improving the efficiency and stability of hybrid perovskite solar cells. However, due to their low concentration, heterogeneous environments, and low sample mass, it remains challenging to characterize their structure and dynamics at the atomic level, as required to establish structure-activity relationships. Nuclear magnetic resonance (NMR) spectroscopy has revealed a wealth of information on the atomic-level structure of hybrid perovskites, but the inherent insensitivity of NMR severely limits its utility to characterize thin-film samples. Dynamic nuclear polarization (DNP) can enhance NMR sensitivity by orders of magnitude, but DNP methods for perovskite materials have so far been limited. Here, we determined the factors that limit the efficiency of DNP NMR for perovskite samples by systematically studying layered hybrid perovskite analogues. We find that the fast-relaxing dynamic cation is the major impediment to higher DNP efficiency, while microwave absorption and particle morphology play a secondary role. We then show that the former can be mitigated by deuteration, enabling 1H DNP enhancement factors of up to 100, which can be harnessed to enhance signals from dopants or additives present in very low concentrations. Specifically, using this new DNP methodology at a high magnetic field and with small sample volumes, we have recorded the NMR spectrum of the 20 nm (6 mu g) passivating layer on a single perovskite thin film, revealing a two-dimensional (2D) layered perovskite structure at the surface that resembles the n = 1 homologue but which has greater disorder than in bulk layered perovskites.

We computationally investigate the impact of crystal strain on the formation of native point defects likely to be formed in halide perovskites; A-site cation antisite (I-A), Pb antisite (I-Pb), A-site cation vacany (V-A), I vacancy (V-I), Pb vacancy (V-Pb), and I interstitial (1). We systematically identify compressive and tensile strain to CsPbI3, FAPbI(3), and MAPbI(3) perovskite structures. We observe that while each type of defect has a unique behaviour, overall, the defect formation in FAPbI(3) is much more sensitive to the strain. The compressive strain can enhance the formation energy of neutral I-pb and I-I up to 15% for FAPbI(3), depending on the growth conditions. We show that the strain not only controls the formation of defects but also their transition levels in the band gap: A deep level can be transformed into a shallow level by the strain. We anticipate that tailoring the lattice strain can be used as a defect passivation mechanism for future studies.

Lead-based perovskites have achieved excellent photovoltaic efficiencies in the last decade, but key intrinsic issues related to their instability and Pb toxicity need to be overcome for their successful commercialization. In this combined experimental–computational study, we investigate the structural and optoelectronic properties of the novel vacancy-ordered lead-free perovskites (CH3NH3)3(Bi1–xSbx)2I9. We find complete miscibility across the solid solution with less than 1% change in the lattice parameters. This miscibility extends to the full configurational disorder between Bi and Sb and a subsequent reduction in the experimentally observed photoluminescence quantum yields. We highlight the significance of the observed band-gap bowing as a means to fine-tune the electronic structure for optoelectronic devices. The substitution of Bi with Sb leads to lower calculated electron and hole effective masses that result in lower exciton binding energies. We show a clear shift from a strongly bound to a weakly bound excitonic regime with the substitution of Bi with Sb, which correlates with the increase in device performance.

Formamidinium lead iodide-based solar cells show promising device reliability. The grain imperfection can be further suppressed by developing powder methodology. The water uptake capability is critical for the stability of α-formamidinium lead triiodide (FAPbI3) thin films, and elucidating the migration of hydrogen species is challenging using routine techniques such as imaging or mass spectroscopy. Here, we decipher the proton diffusion to quantify indirect monitoring of H migration by following the N–D vibration using transmission infrared spectroscopy. The technique allows a direct assessment of the perovskite degradation associated with moisture. The inclusion of Cs in FAPbI3, reveals significant differences in proton diffusion rates, attesting to its impact. CsFAPbI3’s ability to block the active layer access by water molecules is five times higher than α-FAPbI3,which is significantly higher than methylammonium lead triiodide (MAPbI3). Our protocol directly probes the local environment of the material to identify its intrinsic degradation mechanisms and stability, a key requirement for optoelectronic applications.

PbS colloidal quantum dots (CQDs) are versatile building blocks for bottom-up fabrication of various optoelectronic devices. The transport properties of thin films of this class of materials depend on the size of the CQDs, their surface ligands, and stoichiometry. The most common synthetic methods yield PbS CQDs with an excess of Pb atoms, which induces n-type transport properties in CQD films. In this work, we developed a new synthesis, which offers S-rich PbS CQDs. Thanks to their sufficient colloidal stability in nonpolar solvents, we established a protocol for the integration of these CQDs into thin field-effect transistors and found strong hole-dominated transport with a hole mobility of about 1 × 10–2 cm2/Vs. Moreover, we were able to enhance the electron mobility for almost two orders of magnitude while keeping the hole mobility nearly the same. This approach allows us to obtain reliably p-doped PbS CQDs, which can be used for the fabrication of various electronic and optoelectronic devices., Chemistry of Materials, 33 (1), ISSN:0897-4756

The incorporation of a certain amount of Cl ions into methylammonium lead iodide (MAPbI3) perovskite films and how these incorporated Cl ions affect the structural and electronic properties of these films have been an intensively studied topic. In this study, we comprehensively investigated Cl incorporation in MAPbI3 at the atomic scale by a combined study of scanning tunneling microscopy, X-ray photoelectron spectroscopy, ultraviolet and inverse photoemission spectroscopy, density functional theory and molecular dynamics calculations. At a Cl concentration of 14.8 ± 0.6%, scanning tunneling microscopy images confirm the incorporation of Cl ions on the MAPbI3 surface, which also corresponds to the highest surface stability of MAPbI3 found from the viewpoint of both thermodynamics and kinetics by density functional theory and molecular dynamics calculations. Our results show that the Cl concentration is crucial to the surface bandgap and stability of MAPbI3.

Non-fullerene acceptors (NFAs) are excellent light harvesters, yet the origin of their high optical extinction is not well understood. In this work, we investigate the absorption strength of NFAs by building a database of time-dependent density functional theory (TDDFT) calculations of ∼500 π-conjugated molecules. The calculations are first validated by comparison with experimental measurements in solution and solid state using common fullerene and non-fullerene acceptors. We find that the molar extinction coefficient (εd,max) shows reasonable agreement between calculation in vacuum and experiment for molecules in solution, highlighting the effectiveness of TDDFT for predicting optical properties of organic π-conjugated molecules. We then perform a statistical analysis based on molecular descriptors to identify which features are important in defining the absorption strength. This allows us to identify structural features that are correlated with high absorption strength in NFAs and could be used to guide molecular design: highly absorbing NFAs should possess a planar, linear, and fully conjugated molecular backbone with highly polarisable heteroatoms. We then exploit a random decision forest algorithm to draw predictions for εd,max using a computational framework based on extended tight-binding Hamiltonians, which shows reasonable predicting accuracy with lower computational cost than TDDFT. This work provides a general understanding of the relationship between molecular structure and absorption strength in π-conjugated organic molecules, including NFAs, while introducing predictive machine-learning models of low computational cost., J. N., J. Y., D. P., M. A., F. E., and E. R. thank the European Research Council for support under the European Union's Horizon 2020 research and innovation program (Grant Agreement No. 742708 and 648901). The authors at ICMAB acknowledge financial support from the Spanish Ministry of Science and Innovation through the Severo Ochoa” Program for Centers of Excellence in R&D (No. CEX2019-000917-S), and project PGC2018-095411-B-I00. E. R. is grateful to the Fonds de Recherche du Quebec-Nature et technologies (FRQNT) for a postdoctoral fellowship and acknowledges financial support from the European Cooperation in Science and Technology. M. A. thanks the Engineering and Physical Sciences Research Council (EPSRC) for support via doctoral studentships. F. E. thanks the Engineering and Physical Sciences Research Council (EPSRC) for support via the Post-Doctoral Prize Fellowship. X. R.-M. acknowledges Prof. Olle Inganäs and the Knut and Allice Wallenberg Foundation for funding of his current postdoctoral position. H.-L. Yip thanks the support from Guangdong Major Project of Basic and Applied Basic Research (2019B030302007). The TOC figure and Fig. 5a in the manuscript include freely available resources from Flaticon.com. J. Y. thank Xiaodan Ge for her support., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).