Recently, rapid progress in the power
conversion efficiency for
organic solar cells (OSCs) is achieved due to the phenomenal development
of the nonfullerene electron acceptors. In addition to the pairing
electron donors, conjugated donor–acceptor copolymers are another
key player in the high-efficiency OSCs. Here, the temporal evolution
of excited states in a typical copolymer, PM6, was traced by transient
absorption spectroscopy. The spectroscopic result implies the formation
of two kinetically correlated intrachain species, polaron excitons
and intrachain polaron pairs. In the presence of the interchain interaction,
these intrachain species quickly convert into interchain polaron pairs
on a time scale of few picoseconds. Our findings reveal that the electron
transfer mechanisms in PM6-based OSCs substantially depend on the
PM6 environment in the bulk heterojunction blends.
Lead chalcogenide quantum dot (QD) infrared (IR) solar cells are promising devices for breaking through the theoretical efficiency limit of single‐junction solar cells by harvesting the low‐energy IR photons that cannot be utilized by common devices. However, the device performance of QD IR photovoltaic is limited by the restrictive relation between open‐circuit voltages (VOC) and short circuit current densities (JSC), caused by the contradiction between surface passivation and electronic coupling of QD solids. Here, a strategy is developed to decouple this restriction via epitaxially coating a thin PbS shell over the PbSe QDs (PbSe/PbS QDs) combined with in situ halide passivation. The strong electronic coupling from the PbSe core gives rise to significant carrier delocalization, which guarantees effective carrier transport. Benefited from the protection of PbS shell and in situ halide passivation, excellent trap‐state control of QDs is eventually achieved after the ligand exchange. By a fine control of the PbS shell thickness, outstanding IR JSC of 6.38 mA cm−2 and IR VOC of 0.347 V are simultaneously achieved under the 1100 nm‐filtered solar illumination, providing a new route to unfreeze the trade‐off between VOC and JSC limited by the photoactive layer with a given bandgap.
Short video applications have rapidly become one of the most popular online entertainments. It is also one of the most important ways of social networking. However, the request pattern of short videos shows the characteristics of highly dynamic compared to traditional video. First, the access of short video is changing quickly, that is, user shows less preferences. Second, most short videos have no tag descriptions. These result in a significant reduction in caching efficiency of content delivery network (CDN) server, which is used to cache short videos. To address these challenges, this article proposes a recommendation system to optimize short video caching. For lack of tag description, this article proposes event detection method to recognize tags based on improved dense trajectory and concept dictionary video feature extraction. Then the collaborative filtering method is used to generate caching recommendation list for CDN to guide short video caching. Simulation results show that the proposed method can significantly improve the efficiency of short video caching for CDN.
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