Robust Tin‐Based Perovskite Solar Cells with Hybrid Organic Cations to Attain Efficiency Approaching 10%

The stability of a tin‐based perovskite solar cell is a major challenge. Here, hybrid tin‐based perovskite solar cells in a new series that incorporate a nonpolar organic cation, guanidinium (GA⁺), in varied proportions into the formamidinium (FA⁺) tin triiodide perovskite (FASnI₃) crystal structure in the presence of 1% ethylenediammonium diiodide (EDAI₂) as an additive, are reported. The device performance is optimized at a precursor ratio (GAI:FAI) of 20:80 to attain a power conversion efficiency (PCE) of 8.5% when prepared freshly; the efficiencies continuously increase to attain a record PCE of 9.6% after storage in a glove‐box environment for 2000 h. The hybrid perovskite works stably under continuous 1 sun illumination for 1 h and storage in air for 6 days without encapsulation. Such a tin‐based perovskite passes all harsh standard tests, and the efficiency of a fresh device, 8.3%, is certified. The great performance and stability of the device reported herein attains a new milestone for lead‐free perovskite solar cells on a path toward commercial development.     

Crosslinking of polyamides using dianhydrides,diacid chloride and dialdehyde: a promising approach for water treatment

New crosslinked polyamides were successfully produced from the condensation of pre‐synthesized monomer, 5‐(2,2,2‐trifluoroacetamido)isophthaloylchloride (TFAIAC) and diamines at low temperature. These polyamides were used as promising metal‐chelating adsorbents due to the presence of O and N donor sites on the crosslinked polyamides. For this purpose, trifluoroacetic anhydride was used to protect the amino group of 5‐aminoisophthalic acid, thus generating 5‐(2,2,2‐trifluoroacetamido)isophthalic acid (TFAIA). TFAIA was converted into TFAIAC using oxalyl chloride, which was exploited as a suitable monomer for the synthesis of aromatic polyamides. Amino groups were then set free under basic conditions and the crosslinking was carried out through amino groups present on the polyamide chains with different dianhydrides, isophthaloyl chloride and 2,5‐thiophenedicarboxaldehyde. The synthesis of monomers and polymers was confirmed by Fourier transform infrared, ¹H and ¹³C NMR spectroscopy and molar masses of the polyamides were measured by gel permeation chromatography. The crosslinked macromolecules were found to possess enough chain alignment as depicted by their XRD patterns. The thermal stability of the crosslinked polyamides was increased as their decomposition temperatures were improved from 420 to 619 °C. Metal ion uptake was scrutinized through atomic absorption spectroscopy with 83%–85% adsorption capacity at optimized parameters, i.e. a contact time of 3 h at pH 6. The mechanism of adsorption was further investigated through the Freundlich and Langmuir adsorption isotherms. The results reveal that uptake of metal ions followed monolayer adsorption of cations owing to coordination to electronegative centers on the macromolecules, confirming the Langmuir adsorption model. © 2019 Society of Chemical Industry     

Poly[poly(oxypropylene) phosphate] macroionophores for transport and separation of cations in a hybrid: Cation‐exchange polymer and liquid membrane system

Poly[poly(oxypropylene) phosphate]s (PPOPP, M_n = 5800, 8100, 10,400), with different POP units (400, 1200, 2000), were synthesized and applied as cation‐selective macroionophores in a multimembrane hybrid system (MHS). The solution of PPOPP in dichloroethane formed the flowing liquid membrane (FLM) circulating between two polymer cation‐exchange membranes, and subsequently, between two polymer‐made pervaporation (PV) membranes. It was found that the PPOPP macroionophores activate the preferential transport of Zn²⁺ cations from aqueous solutions containing competing Cu²⁺, Ca²⁺, Mg²⁺, K⁺, and Na⁺ cations. The following separation orders were observed for PPOPPs with POP‐400 and POP‐1200: Zn²⁺ > Cu²⁺ ? Ca²⁺, Mg²⁺, K⁺, Na⁺, and for PPOPP with POP‐2000: Zn²⁺ > Cu²⁺,Ca²⁺ ? Mg²⁺, K⁺, Na⁺. Always, the particular cations are separated as: Zn²⁺ > Cu²⁺, Ca²⁺ > Mg²⁺, and K⁺ > Na⁺. The properties of PPOPPs were compared to respective transport and separation characteristics corresponding to those of respective poly(propylene glycol)s and poly(oxypropylene) bisphosphates. The results of investigation indicate that the bifunctional character of PPOPPs is caused by the presence of ionizable groups and probably pseudocyclic POP structures. By comparing the separation of cations in the simple MHS[FLM] system and the system supported by pervaporation unit [MHS[FLM‐PV] it was found that continuous dehydration of an organic FLM improves the system overall performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1436–1445, 2004     

Side chain alkylation of 2-picoline with formaldehyde over alkali modified zeolites

The catalytic side-chain alkylation of 2-picoline with formaldehyde (37 wt/v) was studied over alkali and alkaline earth metal ion modified zeolites in vapor phase conditions at atmospheric pressure, and at a reaction temperature of 300°C. A mixture of vinylpyridine and ethylpyridine were formed by the alkylation of the corresponding picoline over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of side-chain alkylation of 2-picoline was studied over various alkali modified zeolite molecular sieves like ZSM-5 (SiO₂/Al₂O₃ = 30), X, Y, Mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2-picoline when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) and K-Cs-ZSM-5 (30) gave best conversion of 2-picoline and selectivity to vinylpyridine. Cs-ZSM-5 (30) and K-ZSM-5 (30) were employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2-picoline independently. The effects of alkali metal ion content (K, Cs) and precursors of potassium ion on catalytic activity in side-chain alkylation was studied. An attempt has been made to correlate between the basicity with the activity of side-chain alkylation. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed reaction mechanism. The selectivities of 2-vinylpyridine were 81.7, 90.8, and 94.8% at 65.4, 62.1 and 57.2% conversions at 300°C from 2-picoline and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and K-Cs-ZSM-5 (30) respectively. Indian Institute of Chemical technology (IICT) communication no: 020707     

Improved Efficiency and Stability of Perovskite Solar Cells Induced by CO Functionalized Hydrophobic Ammonium‐Based Additives

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_0.83MA_0.17PbI_2.51Br_0.49 perovskite film, thus boosting the efficiency from 17.1 ± 0.8% to 18.6 ± 0.9% for the 0.1 cm² cell and from 15.5 ± 0.5% to 16.5 ± 0.6% for the 1.0 cm² cell. The champion cell shows efficiencies of 20.0% and 17.6% with active areas of 0.1 and 1.0 cm², 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.     

Systematic Efficiency Improvement for Cu2ZnSn(S,Se)4 Solar Cells By Double Cation Incorporation with Cd and Ge

The performance of kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cell is known to be severely limited by the nonradiative recombination near the heterojunction interface and within the bulk of the CZTSSe absorber resulting from abundant recombination centers and limited carrier collection efficiency. Herein, nonradiative recombination is simultaneously reduced by incorporating small amounts of Ge and Cd into the CZTSSe absorber. Incorporation of Ge effectively increases the p-type doping, thus successfully improving the bulk conductance and reducing the recombination in the CZTSSe bulk via enhanced quasi-Fermi level splitting, while the incorporation of Cd greatly reduces defects near the junction region, enabling larger depletion region width and better carrier collection efficiency. The combined effects of Cd and Ge incorporation give rise to systematic improvement in open-circuit voltage (V_OC), short-circuit current density (J_SC), and fill factor (FF), enabling a high conversion efficiency of 11.6%. This study highlights the multiple cation incorporation strategy for systematically manipulating the opto-electronic properties of kesterite materials, which may also be applicable to other semiconductors.     

Reaction of carotenes in palm oil with acid

Carotenes in palm oil reacted with strong acid under nonaqueous conditions to produce blue-green cations that initially absorbed with a broad maximum at approximately 900 nm. These cations were postulated to be formed from the protonation of the α- and β-carotene at the seventh carbon atom, with the charge delocalized between the 8 and 9 conjugated double bonds. They were unstable at room temperature and may, by isomerization and oxidization, form carotenoid compounds with shorter conjugation. The resulting carotenoids can be protonated further to form cations, which absorbed between 500–900 nm, with γ_max of approximately 800 nm. The transient blue-green color observed in partially bleached palm oil is likely due to the presence of these cations.     

Amide Neighbouring‐Group Effects in Peptides: Phenylalanine as Relay Amino Acid in Long‐Distance Electron Transfer

In nature, proteins serve as media for long‐distance electron transfer (ET) to carry out redox reactions in distant compartments. This ET occurs either by a single‐step superexchange or through a multi‐step charge hopping process, which uses side chains of amino acids as stepping stones. In this study we demonstrate that Phe can act as a relay amino acid for long‐distance electron hole transfer through peptides. The considerably increased susceptibility of the aromatic ring to oxidation is caused by the lone pairs of neighbouring amide carbonyl groups, which stabilise the Phe radical cation. This neighbouring‐amide‐group effect helps improve understanding of the mechanism of extracellular electron transfer through conductive protein filaments (pili) of anaerobic bacteria during mineral respiration.     

The preparation and X-ray microanalysis of bulk frozen hydrated vacuolate plant tissue

A series of modifications have been devised which allow the peak to background ratio X-ray analytical method to be used more effectively to measure elemental concentrations in large vacuolate plant cells. Planar, frozen-hydrated fracture faces of bulk plant tissue are coated with a thin film of evaporated chromium, which prevents surface charging. Provided the film is sufficiently thin, c. 5–10 nm, there is no attenuation of the electron beam and only a small absorption of soft X-rays. The chromium makes a small but measurable contribution to the spectral background and suitable corrections may be made to the quantitative results. An improved back-scattered imaging system is described, which helps to overcome the problem of spurious X-ray signals from rough surfaces. The microscope column has been modified to permit a continuous readout of beam current, sensu stricta, during X-ray microanalysis and to allow rapid exchange of the electron gun assembly during low temperature operation. Calculations are given relating the size of the X-ray interactive volume to electron penetration and X-ray emission in both frozen hydrated and frozen dried cells. The problems of X-ray microanalysis are discussed in relation to the highly vacuolate cells found in most mature plant tissues and an example given of the distribution of four major cations in tobacco leaves.