The gray matter volume of the amygdala is correlated with the perception of melodic intervals: a voxel-based morphometry study

Music is not simply a series of organized pitches, rhythms, and timbres, it is capable of evoking emotions. In the present study, voxel-based morphometry (VBM) was employed to explore the neural basis that may link music to emotion. To do this, we identified the neuroanatomical correlates of the ability to extract pitch interval size in a music segment (i.e., interval perception) in a large population of healthy young adults (N = 264). Behaviorally, we found that interval perception was correlated with daily emotional experiences, indicating the intrinsic link between music and emotion. Neurally, and as expected, we found that interval perception was positively correlated with the gray matter volume (GMV) of the bilateral temporal cortex. More important, a larger GMV of the bilateral amygdala was associated with better interval perception, suggesting that the amygdala, which is the neural substrate of emotional processing, is also involved in music processing. In sum, our study provides one of first neuroanatomical evidence on the association between the amygdala and music, which contributes to our understanding of exactly how music evokes emotional responses

Three-dimensional modeling of bipolar charge-carrier transport and recombination in disordered organic semiconductor devices at low voltages

\u3cp\u3eThe electroluminescence from organic light-emitting diodes can be predicted with molecular-scale resolution using three-dimensional kinetic Monte Carlo (3D KMC) simulations [M. Mesta et al., Nat. Mater. 12, 652 (2013)]. However, around and below the built-in voltage KMC simulations are computationally inefficient. 3D master-equation (3D ME) simulation methods, which are fastest for low voltages, are so far mainly available for describing unipolar charge transport. In such simulations, the charge-carrier interactions are treated within a mean-field approach. It is not a priori evident whether such simulations, when applied to bipolar devices, can be extended to include the Coulomb attraction between the individual electrons and holes, so that charge-carrier recombination is sufficiently well described. In this work, we develop a systematic method for extending 3D ME simulations to bipolar devices. The method is applied to devices containing materials with Gaussian energetic disorder, and validated by a comparison with the results of 3D KMC simulations. The comparison shows that the 3D nonuniformity of the molecular-site-resolved carrier concentration and the one-dimensional layer-averaged profile of the recombination rate are fully retained, and that the 3D nonuniformity of the molecular-site-resolved recombination rate is fairly well retained.\u3c/p\u3

Ab initio modeling of steady-state and time-dependent charge transport in hole-only α-NPD devices

We present an ab initio modeling study of steady-state and time-dependent charge transport in hole-only devices of the amorphous molecular semiconductor α–NPD [N,N ′ −Di(1–naphthyl)−N,N ′ −diphenyl−(1,1 ′ −biphenyl)−4,4 ′ −diamine] \u3cbr/\u3eα–NPD [N,N′-Di(1–naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine]\u3cbr/\u3e. The study is based on the microscopic information obtained from atomistic simulations of the morphology and density functional theory calculations of the molecular hole energies, reorganization energies, and transfer integrals. Using stochastic approaches, the microscopic information obtained in simulation boxes at a length scale of ∼10 nm is expanded and employed in one-dimensional (1D) and three-dimensional (3D) master-equation modeling of the charge transport at the device scale of ∼100 nm. Without any fit parameter, predicted current density-voltage and impedance spectroscopy data obtained with the 3D modeling are in very good agreement with measured data on devices with different α-NPD layer thicknesses in a wide range of temperatures, bias voltages, and frequencies. Similarly good results are obtained with the computationally much more efficient 1D modeling after optimizing a hopping prefacto

Ab initio charge-carrier mobility model for amorphous molecular semiconductors

\u3cp\u3eAccurate charge-carrier mobility models of amorphous organic molecular semiconductors are essential to describe the electrical properties of devices based on these materials. The disordered nature of these semiconductors leads to percolative charge transport with a large characteristic length scale, posing a challenge to the development of such models from ab initio simulations. Here, we develop an ab initio mobility model using a four-step procedure. First, the amorphous morphology together with its energy disorder and intermolecular charge-transfer integrals are obtained from ab initio simulations in a small box. Next, the ab initio information is used to set up a stochastic model for the morphology and transfer integrals. This stochastic model is then employed to generate a large simulation box with modeled morphology and transfer integrals, which can fully capture the percolative charge transport. Finally, the charge-carrier mobility in this simulation box is calculated by solving a master equation, yielding a mobility function depending on temperature, carrier concentration, and electric field. We demonstrate the procedure for hole transport in two important molecular semiconductors, α-NPD and TCTA. In contrast to a previous study, we conclude that spatial correlations in the energy disorder are unimportant for α-NPD. We apply our mobility model to two types of hole-only α-NPD devices and find that the experimental temperature-dependent current density-voltage characteristics of all devices can be well described by only slightly decreasing the simulated energy disorder strength.\u3c/p\u3

Equilibrated charge carrier populations govern steady-state nongeminate recombination in disordered organic solar cells

\u3cp\u3eWe employed bias-assisted charge extraction techniques to investigate the transient and steady-state recombination of photogenerated charge carriers in complete devices of a disordered polymer-fullerene blend. Charge recombination is shown to be dispersive, with a significant slowdown of the recombination rate over time, consistent with the results from kinetic Monte Carlo simulations. Surprisingly, our experiments reveal little to no contributions from early time recombination of nonequilibrated charge carriers to the steady-state recombination properties. We conclude that energetic relaxation of photogenerated carriers outpaces any significant nongeminate recombination under application-relevant illumination conditions. With equilibrated charges dominating the steady-state recombination, quasi-equilibrium concepts appear suited for describing the open-circuit voltage of organic solar cells despite pronounced energetic disorder.\u3c/p\u3

Effect of Coulomb correlation on charge transport in disordered organic semiconductors

\u3cp\u3eCharge transport in disordered organic semiconductors, which is governed by incoherent hopping between localized molecular states, is frequently studied using a mean-field approach. However, such an approach only considers the time-averaged occupation of sites and neglects the correlation effect resulting from the Coulomb interaction between charge carriers. Here, we study the charge transport in unipolar organic devices using kinetic Monte Carlo simulations and show that the effect of Coulomb correlation is already important when the charge-carrier concentration is above 10-3 per molecular site and the electric field is smaller than 108 V/m. The mean-field approach is then no longer valid, and neglecting the effect can result in significant errors in device modeling. This finding is supported by experimental current density-voltage characteristics of ultrathin sandwich-type unipolar poly(3-hexylthiophene) (P3HT) devices, where high carrier concentrations are reached.\u3c/p\u3