Abstract:Dielectric constant (K), loss (tan δ), and conductivity (σ) of single crystals of PbI2 are measured (E ∥ c‐axis) as a function of frequency in the range 102 to 107 Hz and at temperatures between 77 to 560 K. At room temperature (≈︁ 303 K), the K‐value at 106 Hz is 6.7. The dielectric constant of this crystals increases slowly with temperature up to about 300 K (this increase being practically frequency‐independent) beyond which the K increase is fast and frequency‐dependent; this later stage of increase of K i… Show more
“…Dielectric constants measured at different temperature cycles show similar reversibility (Figure S12e–h). Based on the rule of mixtures, the ε of perovskite and PbI 2 with their volume fractions should determine the ε of the total system, allowing us to estimate temperature dependence of ε of the MAI-rich single crystal perovskite (see the Supporting Information for details and Figure S12c), which is infeasible to obtain at such a wide range of temperatures due to perovskite decomposition.…”
Perovskite solar cells offer remarkable performance, but further advances will require deeper understanding and control of the materials and processing. Here, we fabricate the first single crystal nanorods of intermediate phase (MAI-PbI 2 -DMSO), allowing us to directly observe the phase evolution while annealing in situ in a high-vacuum transmission electron microscope, which lets up separate thermal effects from other environmental conditions such as oxygen and moisture. We attain the first full determination of the crystal structures and orientations of the intermediate phase, evolving perovskite, precipitating PbI 2 , and ebeam induced PbI 2 during phase conversion and decomposition. Surprisingly, the perovskite decomposition to PbI 2 is reversible upon cooling, critical for long-term device endurance due to the formation of MAI-rich MAPbI 3 and PbI 2 upon heating. Quantitative measurements with a thermodynamic model suggest the decomposition is entropically driven. The single crystal MAPbI 3 nanorods obtained via thermal cycling exhibit excellent mobility and trap density, with full reversibility up to 100 °C (above the maximum temperature for solar cell operation) under high vacuum, offering unique potential for high-performance flexible solar cells.
“…Dielectric constants measured at different temperature cycles show similar reversibility (Figure S12e–h). Based on the rule of mixtures, the ε of perovskite and PbI 2 with their volume fractions should determine the ε of the total system, allowing us to estimate temperature dependence of ε of the MAI-rich single crystal perovskite (see the Supporting Information for details and Figure S12c), which is infeasible to obtain at such a wide range of temperatures due to perovskite decomposition.…”
Perovskite solar cells offer remarkable performance, but further advances will require deeper understanding and control of the materials and processing. Here, we fabricate the first single crystal nanorods of intermediate phase (MAI-PbI 2 -DMSO), allowing us to directly observe the phase evolution while annealing in situ in a high-vacuum transmission electron microscope, which lets up separate thermal effects from other environmental conditions such as oxygen and moisture. We attain the first full determination of the crystal structures and orientations of the intermediate phase, evolving perovskite, precipitating PbI 2 , and ebeam induced PbI 2 during phase conversion and decomposition. Surprisingly, the perovskite decomposition to PbI 2 is reversible upon cooling, critical for long-term device endurance due to the formation of MAI-rich MAPbI 3 and PbI 2 upon heating. Quantitative measurements with a thermodynamic model suggest the decomposition is entropically driven. The single crystal MAPbI 3 nanorods obtained via thermal cycling exhibit excellent mobility and trap density, with full reversibility up to 100 °C (above the maximum temperature for solar cell operation) under high vacuum, offering unique potential for high-performance flexible solar cells.
“…Category 1b has an outer halogen layer added to the metal 32 – 37 and category 1c is category 1b but stretched into an orthorhombic structure. Categories 2, 3, and 4 have a central metal and respectively have a trigonal, tetragonal, and orthorhombic unit cell 38 – 44 . Fig.…”
To realize effective van der Waals (vdW) transistors, vdW dielectrics are needed in addition to vdW channel materials. We study the dielectric properties of 32 exfoliable vdW materials using first principles methods. We calculate the static and optical dielectric constants and discover a large out-of-plane permittivity in GeClF, PbClF, LaOBr, and LaOCl, while the in-plane permittivity is high in BiOCl, PbClF, and TlF. To assess their potential as gate dielectrics, we calculate the band gap and electron affinity, and estimate the leakage current through the candidate dielectrics. We discover six monolayer dielectrics that promise to outperform bulk HfO2: HoOI, LaOBr, LaOCl, LaOI, SrI2, and YOBr with low leakage current and low equivalent oxide thickness. Of these, LaOBr and LaOCl are the most promising and our findings motivate the growth and exfoliation of rare-earth oxyhalides for their use as vdW dielectrics.
“…We have undertaken in our laboratory a programme of work on the growth and study of electrical and optical properties of single crystals of PbI,. Recently we have reported [6] the results of our study on dielectric properties of these samples identifying the defects responsible for intrinsic conduction and the increase in dielectric constant with temperature in the high temperature region. I t is the aim of this paper to report the results of our measurements on the effect of quenching and also X-ray irradiation on the dielectric constant ( K ) and loss (tan 6) which have been measured with electric field parallel to the l ) Kharagpur 721 302, India.…”
The dielectric constant ( K ) , loss (tan a), and conductivity (a) of PbI, single crystals, after quenching and X-ray irradiation are measured in the frequency range 102 to lo7 Hz and in the temperature region 30 to 300 "C. X-ray irradiation of as-grown crystals increases only the low frequency K and tan 6. Quenching (from 370 "C) and X-ray irradiation of these crystals produces the same effect; the changes in K and tan 6 a t room temperature (= 30 "C) are largest in the latter samples. K and tan 6 of the samples subjected to different treatments (like quenching and X-ray irradiation) increase with temperature, the rate of increase is smaller a t higher frequencies; the largest rate of increase is observed in quenched and X-ray irradiated samples. The plot,s log u versus 1/T for these samples give activation energies for conduction in the temperature region 200 to 280 "C as 0.44, 0.41, 0.39, and 0.35 eV for as-grown, quenched, X-ray irradiated and quenched, and X-ray irradiated PbI, crystals, respectively. An attempt is made to understand these results.Es werden die Dielektrizitltskonstante (K), der Verlustfaktor (tg a), und die Leitfahigkeit (a) von Pb1,-Einkristallen nach Abschrecken und Rontgenbestrahlung im Frequenzbereich lo2 bis lo7 Hz und bei Temperaturen zwischen 30 bis 300 "C gemessen. Rontgenbestrahlung der urspriinglich gewachsenen Kristalle ergibt nur einen Anstieg der Niederfrequenz-Dielektrizitatskonstante (K) und des Verlustfaktors tg 6. Abschreckn (von 370 "C) und Rontgenbestrahlung dieser Kristalle ruft den gleichen Effekt hervor ; die Anderungen in K und tg 6 sind bei Zimmertemperatur (= 30 "C) in den letzteren Kristallen am grolten. K und tg 6 der unterschiedlichen Behandlungen ( Abschrecken und Rontgenbestrahlung) ausgesetzten Proben nehmen mit der Temperatur zu, wobei die Anstiegsgeschwindigkeit bei hoheren Frequenzen kleiner ist ; die grolte Anstiegsgeschwindigkeit wird in abgeschreckten und rontgenbestrahlten Proben beobachtet. Die log a-l/T-Kurven dieser Proben ergeben Werte fur die Aktivierungsenergie der Leitfahigkeit im Temperaturbereich 200 bis 280 "C von 0,44; 0,41; 0,39 und 0,35 eV fur ursprungliche, abgeschreckte, rontgenbestrahlte und abgeschreckte bzw. rontgenbestrahlte Pb1,-Kristalle. Es wird der Versuch gemacht, diese Ergebnisse zu verstehen.
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