Search

Carbon dots (CDs), as emerging luminescent nanomaterials, possess excellent but complex properties, bringing about extensive attention and a lot of controversy. In this Perspective, we put forward the concept of "carbonized polymer dots" and emphasize the important role of polymerization and carbonization during the formation of CDs. We explore the common characters and clarify the complicated relationship of CDs, based on the reasonable classification of graphene quantum dots, carbon quantum dots, and carbonized polymer dots. Moreover, different perspectives are provided for comprehensive analysis about the essence of CDs, including quantum dots, molecules, and polymers. The photoluminescence mechanism has been classified into molecule state, carbon core state, surface/edge state, and cross-link enhanced emission effect for further understanding of complicated phenomena.

The crosslink‐enhanced emission effect was first proposed to explore the strong luminescence of nonconjugated polymer dots possessing only either non‐emissive or weakly emissive sub‐luminophores. Interesting phenomena in recent research indicate such enhancement caused by extensive crosslinking appears in diverse luminescent polymers with sub‐luminophores (electron‐rich heteroatomic moieties) or luminophores (conjugated π domains). This enhancement can promote the emission from nonluminous to luminous, from weakly luminous to strongly luminous, and even convert the pathway of radiative transitions. The concept of the crosslink‐enhanced emission effect should be updated and extended to an in‐depth spatial effect, such as electron overlap and energy splitting in confined domains by effective crosslinking, more than initial immobilization. This Minireview outlines the development of the crosslink‐enhanced emission effect from the perspective of the detailed classification, inherent mechanism and applicable systems. An outlook on the further exploration and application of this theory are also proposed. [ABSTRACT FROM AUTHOR]

Abstract: Aqueous‐solution‐processed solar cells (ASCs) are promising candidates of the next‐generation large‐area, low‐cost, and flexible photovoltaic conversion equipment because of their unique environmental friendly property. Aqueous‐solution‐processed polymer/nanocrystals (NCs) hybrid solar cells (AHSCs) can effectively integrate the advantages of the polymer (e.g., flexibility and lightweight) and the inorganic NCs (e.g., high mobility and broad absorption), and therefore be considered as an ideal system to further improve the performance of ASCs. In this work, double‐side bulk heterojunction (BHJ), in which one BHJ combines the active material with electron transport material and the other combines the active material with hole transport material, is developed in the AHSCs. Through comparing with the single‐side BHJ device, promoted carrier extraction, enhanced internal quantum efficiency, extended width of the depletion region, and prolonged carrier lifetime are achieved in double‐side BHJ devices. As a result, power conversion efficiency exceeding 6% is obtained, which breaks the bottleneck efficiency around ≈5.5%. This work demonstrates a device architecture which is more remarkable compared with the traditional only donor–acceptor blended BHJ. Under conservative estimation, it provides instructive architecture not only in the ASCs, but also in the organic solar cells (SCs), quantum dot SCs, and perovskite SCs. [ABSTRACT FROM AUTHOR]

Abstract: Polymer carbon dots (PCDs) are proposed as a new class of room‐temperature phosphorescence (RTP) materials. The abundant energy levels in PCDs increase the probability of intersystem crossing (ISC) and their covalently crosslinked framework structures greatly suppress the nonradiative transitions. The efficient methods allow the manufacture of PCDs with unique RTP properties in air without additional metal complexation or complicated matrix composition. They thus provide a route towards the rational design of metal‐free RTP materials that may be synthesized easily. Furthermore, we find that RTP is associated with a crosslink‐enhanced emission (CEE) effect, which provides further routes to design improved PCDs with diverse RTP performance. Our results show the potential of PCDs as a universal route to achieve effective metal‐free RTP. [ABSTRACT FROM AUTHOR]

Designing highly active and durable electrocatalysts for oxygen evolution reaction (OER) over a wide pH range is of great significance, but it remains challenging. Herein, a defect-rich RuO 2 electrocatalyst with pH-universal OER activity is developed by rationally utilizing the electronic reservoir effect of Mn-coordinated carbonized polymer dots (Mn-CPDs). Mn-CPDs as distinct electron acceptor/donor endows Ru-O sites of RuO 2 with abundant defective structures (i.e., O-Ru-O-Ru-Ru sites and O-Ru-O-Mn units) via reduction-oxidation processes, with incorporated Mn atoms simultaneously feeding electron to Ru. The resultant Ru-O-Mn/CPD exhibits an ultralow OER potential of 196 mV, 194 mV and 251 mV at 10 mA·cm−2 under 0.5 M H 2 SO 4 , 1.0 M KOH, and 1.0 M PBS media, respectively, and long-term catalytic stability, which are among the best OER electrocatalysts. Surprisingly, Ru-O-Mn/CPD also shows great Pt-like hydrogen evolution activity. The theoretical simulation indicates that defective Ru-O-Mn structures produce electron-rich Ru region and near-optimal Ru-4d/O-2p band center, thus optimizing the adsorption/desorption kinetics of key intermediates. [Display omitted] • The defect-rich RuO 2 electrocatalyst was fabricated by utilizing electronic reservoir effect of carbonized polymer dots. • The resultant Ru-O-Mn/CPD exhibits superior pH-universal OER activity and long-term stability. • Ru-O-Mn/CPD shows great Pt-like HER activity in alkaline media. • DFT results indicate defective RuO 2 greatly optimizes OER/HER kinetics. [ABSTRACT FROM AUTHOR]

Despite the various synthesis methods to obtain carbon dots (CDs), the bottom‐up methods are still the most widely administrated route to afford large‐scale and low‐cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom‐up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields. [ABSTRACT FROM AUTHOR]