1,465 research outputs found
Rotational Dynamics of Organic Cations in CH3NH3PbI3 Perovskite
Methylammonium lead iodide (CH3NH3PbI3) based solar cells have shown
impressive power conversion efficiencies of above 20%. However, the microscopic
mechanism of the high photovoltaic performance is yet to be fully understood.
Particularly, the dynamics of CH3NH3+ cations and their impact on relevant
processes such as charge recombination and exciton dissociation are still
poorly understood. Here, using elastic and quasi-elastic neutron scattering
techniques and group theoretical analysis, we studied rotational modes of the
CH3NH3+ cation in CH3NH3PbI3. Our results show that, in the cubic (T > 327K)
and tetragonal (165K < T < 327K) phases, the CH3NH3+ ions exhibit four-fold
rotational symmetry of the C-N axis (C4) along with three-fold rotation around
the C-N axis (C3), while in orthorhombic phase (T < 165K) only C3 rotation is
present. Around room temperature, the characteristic relaxation times for the
C4 rotation is found to be ps while for the C3 rotation ps. The -dependent
rotational relaxation times were fitted with Arrhenius equations to obtain
activation energies. Our data show a close correlation between the C4
rotational mode and the temperature dependent dielectric permittivity. Our
findings on the rotational dynamics of CH3NH3+ and the associated dipole have
important implications on understanding the low exciton binding energy and slow
charge recombination rate in CH3NH3PbI3 which are directly relevant for the
high solar cell performance
PMC21 PATIENT-REPORTED OUTCOMES IN PRODUCT DEVELOPMENT GUIDANCE
Medina Campeny, XavierHomenatge a Mercè Rodoreda amb una reproducció del personatge de la Colometa, a la Plaça del Diamant, novel·la de l'escriptora. Al 1984 es va posar provisionalment a la pl. Rius i Taulet. Al 1990 es va traslladar a l'actual emplaçament
High Resolution Study of Spin Excitations in the Shastry-Sutherland Singlet Ground State of SrCu2(BO3)2
High resolution, inelastic neutron scattering measurements on SrCu2(BO3)2
reveal the dispersion of the three single triplet excitations continuously
across the (H,0) direction within its tetragonal basal plane. These
measurements also show distinct Q dependencies for the single and multiple
triplet excitations, and that these excitations are largely dispersionless
perpendicular to this plane. The temperature dependence of the intensities of
these excitations is well described as the complement of the dc-susceptibility
of SrCu2(BO3)2.Comment: 4 pages, 4 figures. Submitted to PR
A Neutron Elastic Diffuse Scattering Study of PMN
We have performed elastic diffuse neutron scattering studies on the relaxor
Pb(MgNb)O (PMN). The measured intensity distribution near a
(100) Bragg peak in the (hk0) scattering plane assumes the shape of a butterfly
with extended intensity in the (110) and (10) directions. The
temperature dependence of the diffuse scattering shows that both the size of
the polar nanoregions (PNR) and the integrated diffuse intensity increase with
cooling even for temperatures below the Curie temperature K.Comment: Submitted to PR
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