A numerical study of bipolar charging and neutralization of ultrafine particles with uniformly generated heterogeneous ions
JOURNAL OF AEROSOL SCIENCE
Authors: Carsi, M.; Alonso, M.
Abstract
Bipolar charging and neutralization of aerosol particles below 100 nm in a laminar flow tube with a uniform generation rate of mass- and mobility-distributed heterogeneous ions has been studied theoretically, and compared to the case of homogeneous, monodisperse ions. Two types of homogeneous ions have been examined: type-I, having the arithmetic mean mass and mobility of the heterogeneous ions; and type-II, having the same mean mobility but with a mass chosen so as to yield the same mean ion-to-aerosol attachment rate coefficients as the heterogeneous ions. By definition, heterogeneous and homogeneous-II ions lead to the same stationary charge distribution, but homogeneous-I ions lead to a different one. If the bipolar charger operates under nonstationary conditions, each ion type produces a different aerosol charge distribution. Using five different sets of bipolar heterogeneous ion populations, with mobility (and in some cases, mass) distributions measured by different research groups, it has been found that the two types of homogeneous ions, I and II, reproduce with reasonable accuracy the charge distributions yielded by the heterogeneous ions, except for multiply-charged particles in a few specific cases. For the particular charger studied, the stationary charge distribution is attained, within a +/-5% error, when the dimensionless number beta N-in(2i)tau/n(in) introduced in Ibarra, Rodriguez-Maroto, and Alonso (2020) is larger than about 2000. Other charger geometries may lead to a different threshold value for this dimensionless number.
Enhancing the Performance of Organic Solar Cells by Prolonging the Lifetime of Photogenerated Excitons
ADVANCED MATERIALS
Authors: Guo, Qingxin; Liu, Yahui; Liu, Ming; Zhang, Hao; Qian, Xiquan; Yang, Jinjin; Wang, Jing; Xue, Wenyue; Zhao, Qian; Xu, Xinjun; Ma, Wei; Tang, Zheng; Li, Yunliang; Bo, Zhishan
Abstract
Exciton lifetime (tau) is crucial for the migration of excitons to donor/acceptor interfaces for subsequent charge separation in organic solar cells (OSCs); however, obvious prolongation of tau has rarely been achieved. Here, by introducing a solid additive 9-fluorenone-1-carboxylic acid (FCA) into the active layer, which comprises a nonfullerene acceptor, 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6/7-methyl)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2 ',3 '-d ']-s-indaceno[1,2-b:5,6-b ']dithiophene (IT-M), tau is substantially prolonged from 491 to 928 ps, together with obvious increases in fluorescence intensity and quantum yield. Time-resolved transient infrared spectra indicate the presence of an intermolecular vibrational coupling between the electronic excited state of IT-M and the electronic ground state of FCA, which is first observed here and which can suppress the internal conversion process. IT-M-based OSCs display an improved short-circuit current and fill factor after the addition of FCA. Thus, the power conversion efficiency is increased, particularly for devices with a large donor/acceptor ratio of 1:4, whose efficiency is increased by 56%. This study describes a novel method, which is also applicable to other nonfullerene acceptors, for further improving the performance of OSCs without affecting their morphology and light absorption properties.
COA
Publication 
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