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Hollow carbon nanocages (HCNCs) consisting of sp2 carbon shells featured by a hollow interior cavity with defective microchannels (or customized mesopores) across the carbon shells, high specific surface area, and tunable electronic structure, are quilt different from the other nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make HCNCs a new platform for advanced electrochemical energy storage and conversion. This review focuses on the controllable preparation, structural regulation, and modification of HCNCs, as well as their electrochemical functions and applications as energy storage materials and electrocatalytic conversion materials. The metal single atoms-functionalized structures and electrochemical properties of HCNCs are summarized systematically and deeply. The research challenges and trends are also envisaged for deepening and extending the study and application of this hollow carbon material. The development of multifunctional carbon-based composite nanocages provides a new idea and method for improving the energy density, power density, and volume performance of electrochemical energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: High‐performance, cost‐effective hole‐transport materials (HTMs) are greatly desired for the commercialization of perovskite solar cells (PVSCs). Herein, two new HTMs, TPA‐FO and TPA‐PDO, are devised and synthesized, which have a donor‐acceptor‐donor (D‐A‐D) type molecule design featuring carbonyl group‐functionalized arenes as the acceptor (A) units. The carbonyl group at the central core of HTMs can not only tune frontier molecular orbital (FMO) energy levels and surface wettability, but also can enable efficient surface passivation effects, resulting in reduced recombination loss. When employed as HTMs in inverted PVSCs without using dopant, TPA‐FO with one carbonyl group yields a high power conversion efficiency (PCE) of 20.24%, which is among the highest values reported in the inverted PVSCs with dopant‐free HTMs. More importantly, the facile one‐step synthetic process enables a low cost of 30 USD g–1 for TPA‐FO, much cheaper than the most studied HTMs used for high‐efficiency dopant‐free PVSCs. These results demonstrate the potential of D‐A‐D type molecules with carbonyl group‐functionalized arene core in developing the low‐cost dopant‐free HTMs toward highly efficient PVSCs. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: High‐performance, cost‐effective hole‐transport materials (HTMs) are greatly desired for the commercialization of perovskite solar cells (PVSCs). Herein, two new HTMs, TPA‐FO and TPA‐PDO, are devised and synthesized, which have a donor‐acceptor‐donor (D‐A‐D) type molecule design featuring carbonyl group‐functionalized arenes as the acceptor (A) units. The carbonyl group at the central core of HTMs can not only tune frontier molecular orbital (FMO) energy levels and surface wettability, but also can enable efficient surface passivation effects, resulting in reduced recombination loss. When employed as HTMs in inverted PVSCs without using dopant, TPA‐FO with one carbonyl group yields a high power conversion efficiency (PCE) of 20.24%, which is among the highest values reported in the inverted PVSCs with dopant‐free HTMs. More importantly, the facile one‐step synthetic process enables a low cost of 30 USD g–1 for TPA‐FO, much cheaper than the most studied HTMs used for high‐efficiency dopant‐free PVSCs. These results demonstrate the potential of D‐A‐D type molecules with carbonyl group‐functionalized arene core in developing the low‐cost dopant‐free HTMs toward highly efficient PVSCs. [ABSTRACT FROM AUTHOR]