64 research outputs found

    Efficient Planar Perovskite Solar Cells Based on 1.8 eV Band Gap CH<sub>3</sub>NH<sub>3</sub>PbI<sub>2</sub>Br Nanosheets via Thermal Decomposition

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    Hybrid organometallic halide perovskite CH<sub>3</sub>NH<sub>3</sub>PbI<sub>2</sub>Br (or MAPbI<sub>2</sub>Br) nanosheets with a 1.8 eV band gap were prepared via a thermal decomposition process from a precursor containing PbI<sub>2</sub>, MABr, and MACl. The planar solar cell based on the compact layer of MAPbI<sub>2</sub>Br 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 MAPbI<sub>2</sub>Br precursor components (i.e., PbI<sub>2</sub> 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 (CH<sub>3</sub>NH<sub>3</sub>)PbI<sub>3</sub> Sensitized TiO<sub>2</sub> Solar Cells

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    We report on the effect of TiO<sub>2</sub> film thickness on the charge transport, recombination, and device characteristics of perovskite (CH<sub>3</sub>NH<sub>3</sub>)Ā­PbI<sub>3</sub> sensitized solar cells using iodide-based electrolytes. (CH<sub>3</sub>NH<sub>3</sub>)Ā­PbI<sub>3</sub> 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 TiO<sub>2</sub> film thickness from 1.8 to 8.3 Ī¼m has little effect on transport but increases recombination by more than 10-fold, reducing the electron diffusion length from 16.9 to 5.5 Ī¼m, which can be explained by the higher degree of iodide depletion within the TiO<sub>2</sub> pores for thicker films. The changes of the charge-collection and light-absorption properties of (CH<sub>3</sub>NH<sub>3</sub>)Ā­PbI<sub>3</sub> sensitized cells with varying TiO<sub>2</sub> film thickness strongly affect the photocurrent density, photovoltage, fill factor, and solar conversion efficiency. Developing alternative, compatible redox electrolytes is important for (CH<sub>3</sub>NH<sub>3</sub>)Ā­PbI<sub>3</sub> or similar perovskites to be used for potential photoelectrochemical applications

    CH<sub>3</sub>NH<sub>3</sub>Cl-Assisted One-Step Solution Growth of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>: Structure, Charge-Carrier Dynamics, and Photovoltaic Properties of Perovskite Solar Cells

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    We demonstrate a novel one-step solution approach to prepare perovskite CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films by adding CH<sub>3</sub>NH<sub>3</sub>Cl (or MACl) to the standard CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> precursor (equimolar mixture of CH<sub>3</sub>NH<sub>3</sub>I and PbI<sub>2</sub>) solution. The use of MACl strongly affects the crystallization process of forming pure CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, leading not only to enhanced absorption of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> but also to significantly improved coverage of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> on a planar substrate. Compared to the standard one-step solution approach for CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, using MACl improves the performance of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> 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 1ā€“2 orders of magnitude by using MACl. These results suggest that this new one-step solution approach is promising for controlling CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> 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.

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    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 CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Solar Cells: Charge Transport, Recombination, and Diffusion Length

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    We report on the effect of TiO<sub>2</sub> film thickness on charge transport and recombination in solid-state mesostructured perovskite CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (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 TiO<sub>2</sub> 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 TiO<sub>2</sub> film thickness from 240 nm to about 650ā€“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 Ī¼m 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.

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    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.

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    <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 1Ā° 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 CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Perovskite Films via Adjustable Volume Expansion

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    We demonstrate a facile morphology-controllable sequential deposition of planar CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPbI<sub>3</sub>) film by using a novel volume-expansion-adjustable PbI<sub>2</sub>Ā·<i>x</i>MAI (<i>x</i>: 0.1ā€“0.3) precursor film to replace pure PbI<sub>2</sub>. The use of additive MAI during the first step of deposition leads to the reduced crystallinity of PbI<sub>2</sub> and the pre-expansion of PbI<sub>2</sub> into PbI<sub>2</sub>Ā·<i>x</i>MAI with adjustable morphology, which result in about 10-fold faster formation of planar MAPbI<sub>3</sub> film (without PbI<sub>2</sub> 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 PbI<sub>2</sub>Ā·0.15MAI is 17.22% (under one sun illumination), which is consistent with the stabilized maximum power output at an efficiency of 16.9%
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