Composted tobacco waste increases the yield and organoleptic quality of leaf mustard

Tobacco (Nicotiana tabacum) waste is produced in many countries and is phytotoxic due to the alkaloid content; in Vietnam the waste is usually burned causing air pollution. We composted tobacco waste with chicken manure in different proportions—1 t of waste ± accelerant (C1 and C2); 0.8 t of waste + 0.2 t of chicken manure ± accelerant (C3 and C4); and 0.7 t of waste + 0.3 t of chicken manure ± accelerant (C5 and C6)—for 30 d in covered heaps. Three mixtures containing the accelerant (C2, C4, and C6) reached temperatures of ∼55 °C, that 5s, hot enough to suppress disease and weeds. Composting decreased the alkaloid content from ∼6,000 to ∼200 mg kg−1, and C4 with a C/N ratio of 19:1, was used in a field trial. The compost treatments (0, 10, 15, and 20 t ha−1) were combined fertilizer with phosphorus (40 kg ha−1), nitrogen (60 kg ha−1) and potassium (90 kg ha−1) for leaf mustard (Brassica integrifolia). The yield increased from ∼17 to ∼29 t ha−1 with the amount of compost applied, and the nitrate concentration decreased concomitantly from ∼67 to ∼42 mg NO3–N kg−1 fresh weight, presumably due to ongoing composting (nitrogen drawdown). Organoleptic evaluation showed a preference for the crops grown with the compost amendments. Whether remains to be seen whether one-off compost applications >20 t ha−1 and repeated, large applications provide additional, long-term production benefits, or if the benefits may be outweighed by the accumulation of persistent, phytotoxic alkaloids

2D Homologous Perovskites as Light-Absorbing Materials for Solar Cell Applications

We report on the fabrication and properties of the semiconducting 2D (CH₃(CH₂)₃NH₃)₂(CH₃NH₃)_{<i><i>n</i></i><i>–</i>1}Pb_{<i><i>n</i></i>}I_{3<i><i>n</i></i>+1} (<i>n</i> = 1, 2, 3, and 4) perovskite thin films. The band gaps of the series decrease with increasing <i>n</i> values, from 2.24 eV (CH₃(CH₂)₃NH₃)₂PbI₄ (<i>n</i> = 1) to 1.52 eV CH₃NH₃PbI₃ (<i>n</i> = ∞). The compounds exhibit strong light absorption in the visible region, accompanied by strong photoluminescence at room temperature, rendering them promising light absorbers for photovoltaic applications. Moreover, we find that thin films of the semi-2D perovskites display an ultrahigh surface coverage as a result of the unusual film self-assembly that orients the [Pb_{<i><i>n</i></i>}I_{3<i><i>n</i></i>+1}]⁻ layers perpendicular to the substrates. We have successfully implemented this 2D perovskite family in solid-state solar cells, and obtained an initial power conversion efficiency of 4.02%, featuring an open-circuit voltage (<i>V</i>_oc) of 929 mV and a short-circuit current density (<i>J</i>_sc) of 9.42 mA/cm² from the <i>n</i> = 3 compound. This result is even more encouraging considering that the device retains its performance after long exposure to a high-humidity environment. Overall, the homologous 2D halide perovskites define a promising class of stable and efficient light-absorbing materials for solid-state photovoltaics and other applications

The Origin of Lower Hole Carrier Concentration in Methylammonium Tin Halide Films Grown by a Vapor-Assisted Solution Process

A low hole carrier concentration in methylammonium tin halide (MASnX₃) perovskite semiconductors is a prerequisite for a nonshorting solar cell device. In-depth film characterizations were performed on MASnI_3–<i>x</i>Br_<i>x</i> films, fabricated by both a low-temperature vapor-assisted solution process (LT-VASP) and conventional one-step methods, to reveal the origin of the lower hole carrier concentration from films of the former approach. We found that the vaporization of CH₃NH₃I solid at 150 °C, the temperature at which the LT-VASP occurs, does not supply iodine to the SnX₂ (X = Br, I) films. As a result, secondary phases form aside from the desired MASnX₃ perovskite; the secondary phases are suggested to be SnO and Sn­(OH)₂ via a proposed reaction pathway and are further supported by X-ray photoemission spectroscopy (XPS). These nonperovskite Sn²⁺ phases are beneficial because they assist in achieving the lower hole-doping levels in LT-VASP films. Remarkably, LT-VASP devices demonstrate improved air stability. Overall, our findings suggest that not only the commonly used SnF₂ but also other divalent Sn compounds could serve as Sn vacancy suppressors. Further work on modulating the perovskite film compositions could realize more efficient and stable tin-based perovskite solar cells

Overcoming Short-Circuit in Lead-Free CH₃NH₃SnI₃ Perovskite Solar Cells via Kinetically Controlled Gas–Solid Reaction Film Fabrication Process

The development of Sn-based perovskite solar cells has been challenging because devices often show short-circuit behavior due to poor morphologies and undesired electrical properties of the thin films. A low-temperature vapor-assisted solution process (LT-VASP) has been employed as a novel kinetically controlled gas–solid reaction film fabrication method to prepare lead-free CH₃NH₃SnI₃ thin films. We show that the solid SnI₂ substrate temperature is the key parameter in achieving perovskite films with high surface coverage and excellent uniformity. The resulting high-quality CH₃NH₃SnI₃ films allow the successful fabrication of solar cells with drastically improved reproducibility, reaching an efficiency of 1.86%. Furthermore, our Kelvin probe studies show the VASP films have a doping level lower than that of films prepared from the conventional one-step method, effectively lowering the film conductivity. Above all, with (LT)-VASP, the short-circuit behavior often obtained from the conventional one-step-fabricated Sn-based perovskite devices has been overcome. This study facilitates the path to more successful Sn-perovskite photovoltaic research

Introducing Perovskite Solar Cells to Undergraduates

Introducing Perovskite Solar Cells to Undergraduate

Importance of Reducing Vapor Atmosphere in the Fabrication of Tin-Based Perovskite Solar Cells

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the tendency of these materials to form leakage pathways from p-type defect states, mainly Sn⁴⁺ and Sn vacancies, causes poor device reproducibility and limits the overall power conversion efficiencies (PCEs). Here, we present an effective process that involves a reducing vapor atmosphere during the preparation of Sn-based halide perovskite solar cells to solve this problem, using MASnI₃, CsSnI₃, and CsSnBr₃ as the representative absorbers. This process enables the fabrication of remarkably improved solar cells with PCEs of 3.89%, 1.83%, and 3.04% for MASnI₃, CsSnI₃, and CsSnBr₃, respectively. The reducing vapor atmosphere process results in more than 20% reduction of Sn⁴⁺/Sn²⁺ ratios, which leads to greatly suppressed carrier recombination, to a level comparable to their lead-based counterparts. These results mark an important step toward a deeper understanding of the intrinsic Sn-based halide perovskite materials, paving the way to the realization of low-cost and lead-free Sn-based halide perovskite solar cells

Interconversion between Free Charges and Bound Excitons in 2D Hybrid Lead Halide Perovskites

The optoelectronic properties of hybrid perovskites can be easily tailored by varying their components. Specifically, mixing the common short organic cation (methylammonium (MA)) with a larger one (e.g., butyl ammonium (BA)) results in 2-dimensional perovskites with varying thicknesses of inorganic layers separated by the large organic cation. In both of these applications, a detailed understanding of the dissociation and recombination of electron-hole pairs is of prime importance. In this work, we give a clear experimental demonstration of the interconversion between bound excitons and free charges as a function of temperature by combining microwave conductivity techniques with photoluminescence measurements. We demonstrate that the exciton binding energy varies strongly (between 80 and 370 meV) with the thickness of the inorganic layers. Additionally, we show that the mobility of charges increases with the layer thickness, in agreement with calculated effective masses from electronic structure calculations.ChemE/Opto-electronic Material

Amorphous TiO₂ Compact Layers via ALD for Planar Halide Perovskite Photovoltaics

A low-temperature (<120 °C) route to pinhole-free amorphous TiO₂ compact layers may pave the way to more efficient, flexible, and stable inverted perovskite halide device designs. Toward this end, we utilize low-temperature thermal atomic layer deposition (ALD) to synthesize ultrathin (12 nm) compact TiO₂ underlayers for planar halide perovskite PV. Although device performance with as-deposited TiO₂ films is poor, we identify room-temperature UV–O₃ treatment as a route to device efficiency comparable to crystalline TiO₂ thin films synthesized by higher temperature methods. We further explore the chemical, physical, and interfacial properties that might explain the improved performance through X-ray diffraction, spectroscopic ellipsometry, Raman spectroscopy, and X-ray photoelectron spectroscopy. These findings challenge our intuition about effective electron selective layers as well as point the way to a greater selection of flexible substrates and more stable inverted device designs