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1. Boosting Photovoltaic Performance for Lead Halide Perovskites Solar Cells with BF 4 − Anion Substitutions

   https://doi.org/10.1002/adfm.201808833  

   Zhang, Jie ; Wu, Shengfan ; Liu, Tiantian ; Zhu, Zonglong ; Jen, Alex K. ‐Y. ( February 2019 , Advanced Functional Materials)

   Composition engineering is a particularly simple and effective approach especially using mixed cations and halide anions to optimize the morphology, crystallinity, and light absorption of perovskite films. However, there are very few reports on the use of anion substitutions to develop uniform and highly crystalline perovskite films with large grain size and reduced defects. Here, the first report of employing tetrafluoroborate (BF₄⁻) anion substitutions to improve the properties of (FA = formamidinium, MA = methylammonium (FAPbI₃)_0.83(MAPbBr₃)_0.17) perovskite films is demonstrated. The BF₄⁻can be successfully incorporated into a mixed‐ion perovskite crystal frame, leading to lattice relaxation and a longer photoluminescence lifetime, higher recombination resistance, and 1–2 orders magnitude lower trap density in prepared perovskite films and derived solar cells. These advantages benefit the performance of perovskite solar cells (PVSCs), resulting in an improved power conversion efficiency (PCE) of 20.16% from 17.55% due to enhanced open‐circuit voltage (V_OC) and fill factor. This is the highest PCE for BF₄⁻anion substituted lead halide PVSCs reported to date. This work provides insight for further exploration of anion substitutions in perovskites to enhance the performance of PVSCs and other optoelectronic devices.

    

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2. Designing Alternative Non‐Fullerene Molecular Electron Acceptors for Solution‐Processable Organic Photovoltaics

   https://doi.org/10.1002/tcr.201800157  

   Sauvé, Geneviève ( January 2019 , The Chemical Record)

   Until recently, solution‐processable organic photovoltaics (OPVs) mainly relied on fullerene derivatives as then‐type material, paired with ap‐type conjugated polymer. However, fullerene derivatives have disadvantages that limit OPV performance, thus fueling research of non‐fullerene acceptors (NFAs). Initially, NFAs showed poor performance due to difficulties in obtaining favorable blend morphologies. One example is our work with 2,6‐dialkylamino core‐substituted naphthalene diimides. Researchers then learned to control blend morphology by NFA molecular design. To limit miscibility with polymer while preventing excessive self‐aggregation, non‐planar, twisted or 3D structures were reported. An example of a 3D structure is our work with homoleptic zinc(II) complexes of azadipyrromethene. The most recent design is a planar A‐D‐A conjugated system where the D unit is rigid and has orthogonal side chains to control aggregation. These have propelled power conversion efficiencies (PCEs) to ∼14 %, surpassing fullerene‐based OPVs. These exciting new developments prompt further investigations of NFAs and provide a bright future for OPVs.

    

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3. Optical and Structural Properties of Manganese‐Doped Zinc Oxide Grown by Metal‐Organic Chemical Vapor Deposition

   https://doi.org/10.1002/adom.202100096  

   Saravade, Vishal ; Manzoor, Zahra ; Corda, Alexis ; Zhou, Chuanle ; Ferguson, Ian ; Lu, Na ( April 2021 , Advanced Optical Materials)

   This systematic study investigates the optical properties and process−structure−property relationships of Mn‐doped zinc oxide (ZnMnO) grown by metal‐organic chemical vapor deposition with varying Mn‐doping concentration and growth conditions. ZnMnO exhibits a good crystal quality oriented in the (002) direction and contains intermixtures of zinc oxide (ZnO)‐like and manganese oxide (Mn_xO_y)‐like phases. The material exhibits a direct energy absorption band‐edge and a reduction in bandgap with Mn‐doping. Photoluminescence studies show that Mn‐doping can simultaneously tailor broad green band luminescence and ultraviolet edge emissions. Post‐growth air‐annealing results in broad Mn_xO_y‐related photoluminescence emissions at 3.3–4.5 eV. A further reduction in the absorption band‐edge is also observed with annealing. Results indicate that luminescence wavelengths and intensities, and absorption band‐edge can be tuned with the Mn‐doping process. This paper promotes a thorough understanding of defect centers in ZnO with transition metal doping and their interrelation with optical characteristics. The work provides a solid foundation for the development of optoelectronic devices, such as light emitting diodes, solar cells, lasers, and photodetectors using ZnO‐based materials.

    

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4. Absorption spectra of benzoic acid in water at different pH and in the presence of salts: insights from the integration of experimental data and theoretical cluster models

   https://doi.org/10.1039/C9CP06728K  

   Karimova, Natalia V. ; Luo, Man ; Grassian, Vicki H. ; Gerber, R. Benny ( March 2020 , Physical Chemistry Chemical Physics)

   The absorption spectra of molecular organic chromophores in aqueous media are of considerable importance in environmental chemistry. In this work, the UV-vis spectra of benzoic acid (BA), the simplest aromatic carboxylic acid, in aqueous solutions at varying pH and in the presence of salts are measured experimentally. The solutions of different pH provide insights into the contributions from both the non-dissociated acid molecule and the deprotonated anionic species. The microscopic interpretation of these spectra is then provided by quantum chemical calculations for small cluster models of benzoic species (benzoic acid and benzoate anion) with water molecules. Calculations of the UV-vis absorbance spectra are then carried out for different clusters such as C 6 H 5 COOH·(H 2 O) n and C 6 H 5 COO − ·(H 2 O) n , where n = 0–8. The following main conclusions from these calculations and the comparison to experimental results can be made: (i) the small water cluster yields good quantitative agreement with observed solution experiments; (ii) the main peak position is found to be very similar at different levels of theory and is in excellent agreement with the experimental value, however, a weaker feature about 1 eV to lower energy (red shift) of the main peak is correctly reproduced only by using high level of theory, such as Algebraic Diagrammatic Construction (ADC); (iii) dissociation of the BA into ions is found to occur with a minimum of water molecules of n = 8; (iv) the deprotonation of BA has an influence on the computed spectrum and the energetics of the lowest energy electronic transitions; (v) the effect of the water on the spectra is much larger for the deprotonated species than for the non-dissociated acid. It was found that to reproduce experimental spectrum at pH 8.0, additional continuum representation for the extended solvent environment must be included in combination with explicit solvent molecules ( n ≥ 3); (vi) salts (NaCl and CaCl 2 ) have minimal effect on the absorption spectrum and; (vii) experimental results showed that B-band of neutral BA is not sensitive to the solvent effects whereas the effect of the water on the C-band is significant. The water effects blue-shift this band up to ∼0.2 eV. Overall, the results demonstrate the ability to further our understanding of the microscopic interpretation of the electronic structure and absorption spectra of BA in aqueous media through calculations restricted to small cluster models. 

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5. Multipurpose made colorimetric materials for amines, pH change and metal ion detection

   https://doi.org/10.1039/d1ra07811a  

   Bao, Lihong ; Jones, Leighton O. ; Garrote Cañas, Ana M. ; Yan, Yunhan ; Pask, Christopher M. ; Hardie, Michaele J. ; Mosquera, Martin A. ; Schatz, George C. ; Sergeeva, Natalia N. ( January 2022 , RSC Advances)

   Sensors are routinely developed for specific applications, but multipurpose sensors are challenging, due to stability and poor functional design. We report organic materials that operate in solution and gas phase. They show a strong response behaviour to at least three types of environmental changes: pH, amine and metal ion binding/detection. We have confirmed and validated our findings using various analytical and computational methods. We found that the changes in polarity of the solvent and pH not only red shift the tail of the absorption spectra, but also extend the peak optical absorption of these structures by up to 100 nm, with consequential effects on the optical gap and colour changes of the materials. Acid–base response has been studied by spectrophotometric titrations with trifluoroacetic acid (TFA) and triethyl amine (TEA). The experiments show excellent reversibility with greater sensitivity to base than acid for all compounds. Analysis into metal sensing using Zn( ii ) and Cu( ii ) ions as analytes show that the materials can successfully bind the cations forming stable complexes. Moreover, a strong suppression of signal with copper gives an operative modality to detect the copper ion as low as 2.5 × 10 −6 M. The formation of the metal complexes was also confirmed by growing crystals using a slow diffusion method; subsequent single crystal X-ray analysis reveals the ratio of ligand to metal to be 2 to 1. To test sensitivity towards various amine vapours, paper-based sensors have been fabricated. The sensors show a detection capability at 1 ppm of amine concentration. We have employed CIE L * a * b * colour space as the evaluation method, this provides numeric comparison of the samples from different series and allows comparison of small colour differences, which are generally undetectable by the human-eye. It shows that the CIE L * a * b * method can assess both sensitivity to a particular class of analytes and a specificity response to individual amines in this subclass offering an inexpensive and versatile methodology. 

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