No abstract

A crucial issue facing polymer-based solar cells is how to manage the energetics of the polymer/fullerene blends to maximize short-circuit current density and open-circuit voltage at the same time and thus the power conversion efficiency. Here we demonstrate that the use of a naphthobisoxadiazole-based polymer with a narrow bandgap of 1.52 eV leads to high open-circuit voltages of approximately 1 V and high-power conversion efficiencies of ∼9% in solar cells, resulting in photon energy loss as small as ∼0.5 eV, which is much smaller than that of typical polymer systems (0.7–1.0 eV). This is ascribed to the high external quantum efficiency for the systems with a very small energy offset for charge separation. These unconventional features of the present polymer system will inspire the field of polymer-based solar cells towards further improvement of power conversion efficiencies with both high short-circuit current density and open-circuit voltage.

Metal chalcogenides, pnictides, and carbides, labeled collectively as metal X-ides, have become an exciting new class of water oxidation electrocatalysts, but there is a lack of agreement regarding the composition of the "true" catalyst. The most prominent theories are that the X-ides are either completely oxidized, left unoxidized, or transformed into core@shell particles upon testing. Here, we examine examples of each conjecture, summarizing the conflicting viewpoints on catalyst identity and offering guidelines for more rigorous identification in the future. Most studies indicate that at least partial oxidation of the catalyst surface is critical to high performance, likely caused by an increased catalyst surface area upon oxidation or improved charge transfer in the X-ide cores. Therefore, more thorough and uniform long-term testing and nanoscale chemical analysis are essential to determine how these factors relate to catalyst performance.