Reversible Anion Exchange Reaction in Solid Halide Perovskites and Its Implication in Photovoltaics

Anion exchange reaction is a particularly versatile tool for the synthesis of a large class of nanomaterials. Here we report a low temperature, fast, reversible anion exchange reaction in halide perovskite thin film. Although processed in the solid-state phase, the exchanged hybrid perovskite shows good quality in terms of morphology conservation, phase transformation, and homogeneous composition. The easily exchanged reaction during the crystallization process suggests the robust nature of the Pb–CH₃NH₃ framework and high diffusion ability of halide ions in the perovskite lattice. Furthermore, we show its application in perovskite solar cells; we find that the anion exchange reaction does not induce any remarkable defects resulting from the lattice transformation and morphology reconstruction. In some case, the beneficial exchange of halide species involving simultaneous displacement reaction and crystallization can be used to improve the perovskite solar cell performance. Our work provides new physical insight into understanding the perovskite formation mechanism and the ionic behavior in the perovskite

Nanopyramid Structure for Ultrathin c‑Si Tandem Solar Cells

Recently, ultrathin crystalline silicon solar cells have gained tremendous interest because they are deemed to dramatically reduce material usage. However, the resulting conversion efficiency is still limited by the incomplete light absorption in such ultrathin devices. In this letter, we propose ultrathin a-Si/c-Si tandem solar cells with an efficient light trapping design, where a nanopyramid structure is introduced between the top and bottom cells. The superior light harvesting results in a 48% and 35% remarkable improvement of the short-circuit current density for the top and bottom cells, respectively. Meanwhile, the use of SiO_<i>x</i> mixed-phase nanomaterial helps to provide the maximum light trapping without paying the price of reduced electrical performance, and conversion efficiencies of up to 13.3% have been achieved for the ultrathin tandem cell employing only 8 μm of silicon, which is 29% higher than the result obtained for the planar cell

Impact of pre-treatment with DMTU or DPI on SA-induced ARF in mung bean hypocotyl cuttings.

<p>The primary roots were removed from seedlings of 5-day-old germinated mung beans, incubated in DMTU or DPI for 4 h, moved into 0.4 mM SA for 24 h, washed three times and cultivated in distilled water for another five days. The number of adventitious roots was quantified and is expressed as the mean from three independent experiments with 30 explants for each treatment. The different letters above the bars indicate significant differences among the treatments (P<0.05), according to the LSD test. </p

Time course of H₂O₂ accumulation (a) and O^2– production (b) in the hypocotyls of mung beans treated with water or SA.

<p>Explants were incubated with SA or water for 24 h, and the H₂O₂ levels were monitored at the indicated time points. The mean values shown are the averages of three different experiments. The error bars represent the SE (n=5). The asterisks indicate that the mean values are significantly different compared with the control values (P<0.05). FW, fresh weight.</p

Histochemical and cytochemical detection of H₂O₂ accumulation induced by SA in mung bean hypocotyl cuttings.

<div><p>a Mung bean hypocotyl cuttings were incubated in SA for 24 h, and H₂O₂ levels were monitored at the indicated time points. All experiments were repeated at least three times with similar results. Bar=1 cm.</p> <p>b Mung bean hypocotyl cuttings were incubated in SA for 12 h. Hypocotyls treated with distilled water under the same conditions served as controls. All experiments were repeated at least three times with similar results. Abbreviations: CW, cell wall; IS, intercellular space. Bar=1 µm.</p></div

Interaction between SA in combination with H₂O₂ on ARF in mung bean hypocotyls.

<p>Hypocotyls were treated with different test solutions for 24 h, and then the cuttings were transferred to distilled water and continuously grown for 5 days at 25±2°C, with a 14-h photoperiod (PAR of 200 µmol m⁻² s⁻¹). The distilled water was replaced every day, and the number of adventitious roots of more than 1 mm long was recorded. The number of roots was determined after 5 d of treatment. The values represent the means of 30 explants, and the error bars represent the SE (P<0.05). H₂O₂:10 mM H₂O₂.</p

SA-induced ARF increases in mung bean hypocotyl cuttings.

<p>(a) Hypocotyls were incubated with 0, 0.1, 0.2, 0.4, 0.6 and 0.8 mM SA for 24 h and washed three times, and then the cuttings were transferred into distilled water. The cuttings were continuously grown for 5 days in this distilled water at 25±2°C, with a 14-h photoperiod (PAR of 200 µmol m⁻² s⁻¹). The distilled water was replaced every day. The root numbers were determined at 5 d after treatment. In addition, adventitious roots of more than 1 mm long were quantified. The values represent the means of 30 explants, and the different letters above the bars indicate significant differences among the treatments at a P<0.05 level, according to the LSD test. (b) Time course of adventitious root formation induced by application of SA or water in mung bean hypocotyls. Hypocotyls were treated with 0.4 mM SA (the optimal concentration) or CK (water) for 24 h and were then transferred into distilled water and continuously grown for 7 days at 25±2°C, with a 14-h photoperiod (PAR of 200 µmol m⁻² s⁻¹). The root numbers were determined in 24-h intervals. The distilled water was replaced every day, and the number of adventitious roots of more than 1 mm long was recorded. The values represent the means of 30 explants, and the error bars represent the SE (P<0.05) .</p

(a)Photograph showing explants after 5 days of treatment with CK (water) and SA (0.4 mM) Bar=1 cm.

<p>(b)Photograph depicting adventitious root primordial formation in mung bean seedlings after 48 h of treatment with H₂O or 0.4 mM SA. Bar=1 mm.</p

Time course of changes in the activities of the antioxidant enzymes SOD (a), CAT (b), GR(c) and APX (d) in the hypocotyls of mung beans treated with water or SA.

<p>Explants were incubated with SA or water for 24 h, and the enzyme actives were monitored at the indicated time point. The mean values shown are the averages of three different experiments. The error bars represent the SE (n=5). Asterisks indicate that the mean values are significantly different compared with the control values (P<0.05). FW, fresh weight.</p

Controllable Transformation of 2D Perovskite for Multifunctional Sensing Properties

There is growing demand for convenient and cost-efficient ethanol sensing techniques in daily life and industry. However, the complexity, high cost, and large volume of the equipment hinder the widespread use of conventional ethanol sensing techniques. Here, we introduce a test paperlike visualized label-free ethanol sensing platform by taking advantage of the instability of 2D Ruddlesden–Popper perovskite in ethanol. The photoluminescence of PEA2Csn–1PbnBr3n+1 2D perovskite changes from deep blue to green distinctly when exposed to ethanol. A cheap demo ethanol test paper is fabricated by this 2D perovskite and paper using a simple method, demonstrating interesting rapid and convenient ethanol sensing performance. Crystal analysis, constituent analysis, spectral analysis, and molecular dynamic (MD) simulation reveal the crystal structure transformation from 2D to 3D induced by the migration of PEA+ cations in the original 2D perovskite when exposed to ethanol. In addition, a chemiresistive sensor based on the 2D perovskite and on the 2D–3D phase transformation is developed and demonstrates a high ethanol detection sensitivity with a limit down to 0.7 ppm. The photodetector fabricated by the 2D perovskite also demonstrates tunable sensitivity upon the controllable 2D–3D transformation. This remarkable colorimetric, chemiresistive, and photosensitive perovskite is expected to highlight its future application and be a supplement to the existing ethanol sensing and photodetector techniques