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New publication in Nature Communications

(a) Photograph of the CH3NH3PbI3 single crystal annealed at 100 C. (b) Transient
reflectivity signal revealing coherent phonon oscillations arising from the coupling of photoexcited electrons to the lattce. Inset: Fourier transform
of the oscillatory component

The Yartsev Group has published a new article in Nature Communications entitled "Electron–acoustic phonon coupling in single crystal CH3NH3PbI3 perovskites revealed by coherent acoustic phonons"

"Despite the great amount of attention CH3NH3PbI3 has received for its solar cell application, intrinsic properties of this material are still largely unknown. Mobility of charges is a quintessential property in this aspect; however, there is still no clear understanding of electron transport, as reported values span over three orders of magnitude. Here we develop a method to measure the electron and hole deformation potentials using coherent acoustic phonons generated by femtosecond laser pulses. We apply this method to characterize a CH3NH3PbI3 single crystal. We measure the acoustic phonon properties and characterize electron-acoustic phonon scattering. Then, using the deformation potential theory, we calculate the carrier intrinsic mobility and compare it to the reported experimental and theoretical values. Our results reveal high electron and hole mobilities of 2,800 and 9,400 cm2 V−1 s−1, respectively. Comparison with literature values of mobility demonstrates the potential role played by polarons in charge transport in CH3NH3PbI3."


New publication in ACS Omega

The Scheblykin Group has published a new article in ACS Omega entitled Macroscopic Domains within an Oriented TQ1 Film Visualized Using 2D Polarization Imaging

"Large-area self-assembly of functional conjugated polymers holds a great potential for practical applications of organic electronic devices. We obtained well-aligned films of poly[2,3-bis(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) using the floating film transfer method. Thereby, a droplet of the TQ1 solution was injected on top of the surface of an immiscible liquid substrate, at the meniscus formed at the edge of a Petri dish, from where the polymer solution and the film spread in one direction. Characterization of the TQ1 film using the recently developed two-dimensional polarization imaging (2D POLIM) revealed large, millimeter-sized domains of oriented polymer chains. The irregular shape of the contact line at the droplet source induced the appearance of disordered stripes perpendicular to the spreading direction. A correlation of polarization parameters measured using 2D POLIM revealed the microstructure of such stripes, providing valuable information for further improvement and possible upscaling of this promising method."


Photonics Sweden Student Award

Lukas Wittenbecher (L) receiving the Photonics Sweden Award, Linköping, Nov 2016

Lukas Wittenbecher has won first prize in the Photonics Sweden Student Award

The award was given for the work undertaken during his masters project at Chemical Physics. His thesis concerned "Compression and Shaping of Femtosecond Laser Pulses for Coherent Two-Dimensional Nanoscopy".




Figure. Single molecule spectroscopy of individual fluorescing polymer chains: their appearance in a fluorescence microscope (top left) and their blinking or fluctuating between a neutral (bright) and charged (dark) states (top right), together with calculated electronic properties of a light-harvesting polymer (bottom).

Mastering Morphology for Solution-borne Electronics

Researchers from the Chemistry Department participate in a new project that has been granted 28 MSEK support by the Knut and Alice Wallenberg Foundation.

Professor Ivan Scheblykin (Chemical Physics) and University Lecturer Petter Persson (Theoretical Chemistry) from the Chemistry Department at Lund University participate in a new project ”Mastering Morphology for Solution-borne Electronics” that has been granted 28 MSEK support by the Knut and Alice Wallenberg Foundation (2016-10-05). The goal of the new project is to make efficient solar cells from molecular semiconductors through improved processing technology and better understanding of how the fundamental molecular interactions govern the structure in these functional materials. The project is a collaboration between researchers from Karlstad University, Lund University, Chalmers, and Linköping University led by Professor Ellen Moons in Karlstad. The research at the Chemistry Department in Lund will focus on material characterization through a combination of spectroscopy, microscopy and computational chemistry.

 

Press release from KAW (in Swedish)

Press release from Karlstad University (in Swedish)


New publication in Nano Letters


SEM images of six nano-objects overlaid with polar plots showing the polarizations of PL excitation (blue) and PL emission (red) at 77 K (a–d), 152 K (e–h), and 295 K (i–l). The modulation depths for each nano-object are given in red (Mem) and in blue (Mex)

The Scheblykin Group has published a new article in Nano Letters entitled "Exploring the Electronic Band Structure of Organometal Halide Perovskite via Photoluminescence Anisotropy of Individual Nanocrystals"

"Understanding electronic processes in organometal halide perovskites, flourishing photovoltaic, and emitting materials requires unraveling the origin of their electronic transitions. Light polarization studies can provide important information regarding transition dipole moment orientations. Investigating individual methylammonium lead triiodide perovskite nanocrystals enabled us to detect the polarization of photoluminescence intensity and photoluminescence excitation, hidden in bulk samples by ensemble averaging. Polarization properties of the crystals were correlated with their photoluminescence spectra and electron microscopy images. We propose that distortion of PbI6 octahedra leads to peculiarities of the electronic band structure close to the band-edge. Namely, the lowest band transition possesses a transition dipole moment along the apical Pb–I–Pb bond resulting in polarized photoluminescence. Excitation of photoluminescence above the bandgap is unpolarized because it involves molecular orbitals delocalized both in the apical and equatorial directions of the perovskite octahedron. Trap-assisted emission at 77 K, rather surprisingly, was polarized similar to the bandgap emission."