Nonfullerene
acceptors (NFAs) have attracted great attention in
high-efficiency organic solar cells (OSCs). While the effect of molecular
properties including structures and energetics on charge transfer
has been extensively investigated, the effect of macroscopic-phase
properties is yet to be revealed. Here we have performed a correlation
study of the nanoscale-phase morphology on the photoexcited hole transfer
(HT) process and photovoltaic performance by combining ultrafast spectroscopy
with high temporal resolution and photo-induced force microscopy (PiFM)
with high spatial and chemical resolution. In PM6/IT-4F, we observe
biphasic HT behavior with a minor ultrafast (<100 fs) interfacial
process and a major diffusion-mediated HT process until ∼100
ps, which depends strongly on phase segregation. Because of the interplay
between charge transfer and transport, a compromised domain size of
20–30 nm for NFAs shows the best performance. This study highlights
the critical role of phase morphology in high-efficiency OSCs.
Black carbon (BC) particles become hydrophilic after mixing with soluble matter in the atmosphere, and their optical and radiative properties can be significantly modified accordingly. This study investigates the impact of aggregate structure on optical and radiative properties of aged BC, that is, BC coated by sulfate or organic aerosols, especially during hygroscopic growth. A more realistic BC morphology based on fractal aggregates is considered, and inhomogeneous mixtures of BC aggregates are treated more realistically (with respect to particle geometries) in the multiple sphere T‐matrix method for optical property simulations. As relative humidity increases, BC extinction is significantly enhanced due to an increase in scattering, and the enhancement depends on the amount and hydrophilicity of the coating. The absorption exhibits less variation during hygroscopic growth because the coating of aerosols already leads to BC absorption close to the maximum. Furthermore, hygroscopic growth not only results in negative radiative forcing (RF) at the top of the atmosphere but also slightly weakens the absorption in the atmosphere (inducing a negative RF in the atmosphere). Compared to the more realistic model with BC as aggregates, the currently popular core‐shell model reasonably approximates the top of the atmosphere RF but underestimates the atmospheric RF due to hygroscopic growth by up to 40%. Furthermore, for the RF caused by internal mixing, the core‐shell model overestimates the RFs at the surface and in the atmosphere by ~10%.
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