Efficient Planar Perovskite Solar Cells Based on 1.8 eV Band Gap CH₃NH₃PbI₂Br Nanosheets via Thermal Decomposition

Hybrid organometallic halide perovskite CH₃NH₃PbI₂Br (or MAPbI₂Br) nanosheets with a 1.8 eV band gap were prepared via a thermal decomposition process from a precursor containing PbI₂, MABr, and MACl. The planar solar cell based on the compact layer of MAPbI₂Br nanosheets exhibited 10% efficiency and a single-wavelength conversion efficiency of up to 86%. The crystal phase, optical absorption, film morphology, and thermogravimetric analysis studies indicate that the thermal decomposition process strongly depends on the composition of precursors. We find that MACl functions as a glue or soft template to control the initial formation of a solid solution with the main MAPbI₂Br precursor components (i.e., PbI₂ and MABr). The subsequent thermal decomposition process controls the morphology/surface coverage of perovskite films on the planar substrate and strongly affects the device characteristics

Charge Transport and Recombination in Perovskite (CH₃NH₃)PbI₃ Sensitized TiO₂ Solar Cells

We report on the effect of TiO₂ film thickness on the charge transport, recombination, and device characteristics of perovskite (CH₃NH₃)­PbI₃ sensitized solar cells using iodide-based electrolytes. (CH₃NH₃)­PbI₃ is relatively stable in a nonpolar solvent (e.g., ethyl acetate) with a low iodide concentration (e.g., 80 mM). Frequency-resolved modulated photocurrent/photovoltage spectroscopies show that increasing TiO₂ film thickness from 1.8 to 8.3 μm has little effect on transport but increases recombination by more than 10-fold, reducing the electron diffusion length from 16.9 to 5.5 μm, which can be explained by the higher degree of iodide depletion within the TiO₂ pores for thicker films. The changes of the charge-collection and light-absorption properties of (CH₃NH₃)­PbI₃ sensitized cells with varying TiO₂ film thickness strongly affect the photocurrent density, photovoltage, fill factor, and solar conversion efficiency. Developing alternative, compatible redox electrolytes is important for (CH₃NH₃)­PbI₃ or similar perovskites to be used for potential photoelectrochemical applications

CH₃NH₃Cl-Assisted One-Step Solution Growth of CH₃NH₃PbI₃: Structure, Charge-Carrier Dynamics, and Photovoltaic Properties of Perovskite Solar Cells

We demonstrate a novel one-step solution approach to prepare perovskite CH₃NH₃PbI₃ films by adding CH₃NH₃Cl (or MACl) to the standard CH₃NH₃PbI₃ precursor (equimolar mixture of CH₃NH₃I and PbI₂) solution. The use of MACl strongly affects the crystallization process of forming pure CH₃NH₃PbI₃, leading not only to enhanced absorption of CH₃NH₃PbI₃ but also to significantly improved coverage of CH₃NH₃PbI₃ on a planar substrate. Compared to the standard one-step solution approach for CH₃NH₃PbI₃, using MACl improves the performance of CH₃NH₃PbI₃ solar cells from about 2% to 12% for the planar cell structure and from about 8% to 10% for the mesostructured device architecture. Although we find no significant effect of using MACl on charge transport and recombination in mesostructured perovskite cells, the recombination resistance for planar cells increases by 1–2 orders of magnitude by using MACl. These results suggest that this new one-step solution approach is promising for controlling CH₃NH₃PbI₃ growth to achieve high-performance perovskite solar cells

Appendix B. Additional statistical results, including models using alternative metrics for biotic velocity, models without phylogenetic error structure, and models including dually colonized species.

Additional statistical results, including models using alternative metrics for biotic velocity, models without phylogenetic error structure, and models including dually colonized species

Solid-State Mesostructured Perovskite CH₃NH₃PbI₃ Solar Cells: Charge Transport, Recombination, and Diffusion Length

We report on the effect of TiO₂ film thickness on charge transport and recombination in solid-state mesostructured perovskite CH₃NH₃PbI₃ (via one-step coating) solar cells using spiro-MeOTAD as the hole conductor. Intensity-modulated photocurrent/photovoltage spectroscopies show that the transport and recombination properties of solid-state mesostructured perovskite solar cells are similar to those of solid-state dye-sensitized solar cells. Charge transport in perovskite cells is dominated by electron conduction within the mesoporous TiO₂ network rather than from the perovskite layer. Although no significant film-thickness dependence is found for transport and recombination, the efficiency of perovskite cells increases with TiO₂ film thickness from 240 nm to about 650–850 nm owing primarily to the enhanced light harvesting. Further increasing film thickness reduces cell efficiency associated with decreased fill factor or photocurrent density. The electron diffusion length in mesostructured perovskite cells is longer than 1 μm for over four orders of magnitude of light intensity

Appendix A. Exampe figure detailing the calculation of climate tracking metrics for the contemporary data set using forest inventory and analysis data.

Exampe figure detailing the calculation of climate tracking metrics for the contemporary data set using forest inventory and analysis data

Supplement 1. Latitudinal difference distributions, associated rates of temperature change, and trait values for each species in the contemporary data set.

<h2>File List</h2><div> <p><a href="LDD_for_Northern_Edge.csv">LDD_for_Northern_Edge.csv</a> (MD5: 8963d2b01800440c827e56c38d3d80d4)</p> <p><a href="LDD_for_Southern_Edge.csv">LDD_for_Southern_Edge.csv</a> (MD5: c6cf2c82cb42d15b106f12a58ebdd501)</p> </div><h2>Description</h2><div> <p>The LDD_for_Northern_Edge.csv and LDD_for_Southern_Edge.csv files are comma delimited files. They contain species level data on latitudinal difference distributions at the northern and southern range edges, respectively, along with associated climate velocities.</p> <p>Columns</p> <p>1. FIA species code = USFS numerical code for each tree species </p> <p>2. Common name = species common name, following USFS conventions</p> <p>3. Species = latin binomial for each tree species</p> <p>4. Family = Botanical family of each tree species</p> <p>5. Mycorrhizal Guild = type of mycorrhizal association (AM = arbuscular mycorrhizal, EM = ectomycorrhizal, Dual = dually colonized by both AM and EM fungi)</p> <p>6. Shade Tolerance = numerical rank denoting qualitative shade tolerance scores (1 = Very intolerant, 2 = Intolerant, 3 = Intermediate, 4 = Tolerance, 5 = Very Tolerant)</p> <p>7. ln(Seed Size) = Species mean seed mass, natural log transformed</p> <p>8. Climate Velocity = rate of temperature change at the northern (or southern) range boundary over the last century</p> <p>9. LDD = Species mean Latitudinal difference distribution using the methods described in main text (based on median latitude of observations within 1° latitude of most extreme tree observation).</p> <p>10. LDD 95% CI = 95% confidence intervals of species mean LDD across longitudinal bands</p> <p>11. LDD (using minimum observation) = Species mean Latitudinal difference distribution using only the most extreme observations of trees and seedlings</p> <p>12. LDD 95% CI = 95% confidence intervals of species mean LDD using minimum observations across longitudinal bands</p> <p>13. LDD (using minimal 5% of observations) = Species mean Latitudinal difference distribution using the observations at the 5% (southern edge) or 95% (northern edge) of observations.</p> <p>14. LDD 95% CI = 95% confidence intervals of species mean LDD using 5 percentile observations across longitudinal bands</p> <p>15. BV-CV = biotic velocity minus climate velocity, calculated by subtracting column 8 from column 9.</p> <p>16. BV-CV (using minimal observation) = biotic velocity minus climate velocity, calculated by subtracting column 8 from column 10.</p> <p>17. BV-CV (using minimal 5% of observations) = biotic velocity minus climate velocity, calculated by subtracting column 8 from column 11.</p> </div

Controllable Sequential Deposition of Planar CH₃NH₃PbI₃ Perovskite Films via Adjustable Volume Expansion

We demonstrate a facile morphology-controllable sequential deposition of planar CH₃NH₃PbI₃ (MAPbI₃) film by using a novel volume-expansion-adjustable PbI₂·<i>x</i>MAI (<i>x</i>: 0.1–0.3) precursor film to replace pure PbI₂. The use of additive MAI during the first step of deposition leads to the reduced crystallinity of PbI₂ and the pre-expansion of PbI₂ into PbI₂·<i>x</i>MAI with adjustable morphology, which result in about 10-fold faster formation of planar MAPbI₃ film (without PbI₂ residue) and thus minimize the negative impact of the solvent isopropanol on perovskites during the MAI intercalation/conversion step. The best efficiency obtained for a planar perovskite solar cell based on PbI₂·0.15MAI is 17.22% (under one sun illumination), which is consistent with the stabilized maximum power output at an efficiency of 16.9%

Appendix A. Data used in calculating the reported results for 48 species of trees and treelets at Cocha Cashu Biological Station in Peru.

Data used in calculating the reported results for 48 species of trees and treelets at Cocha Cashu Biological Station in Peru

Lewis Acid-Catalyzed Cyclization of Enaminones with Propargylic Alcohols: Regioselective Synthesis of Multisubstituted 1,2-Dihydropyridines

A highly efficient BF₃·Et₂O-catalyzed cascade reaction of enaminones with propargylic alcohols under mild reaction conditions has been developed. This methodology offers regioselective access to multisubstituted 1,2-dihydropyridines in good to excellent yields