Biomass Derived Self-Doped Carbon Nanosheets Enable Robust Hole Transport Layers with Ion Buffer for Perovskite Solar Cells.

The diffusion of iodine species and lead leakage during device degradation represent the main obstacles restricting the commercial application of perovskite solar cells (PSCs). Cobalt loaded ultrathin carbon nanosheets (Co(III)-CNS) derived from biomass are prepared as ion buffer material to construct robust hole transport layers (HTLs). The carbon nanosheets containing trivalent cobalt ions can facilitate the oxidation of the hole transport material while preserving the structural integrity and electrical properties of HTLs under thermal stress, thereby ensuring efficient carrier transport. The two-dimensional ultrathin graphitized lamellar structure of Co(III)-CNS is conducive to alleviate the corrosive effects of the outward diffusion of iodine species on HTLs and silver electrodes, while avoiding irreversible degradation of PSCs. With the improvement of HTL composition and the related interfaces, Co(III)-CNS doped devices can maintain intact device structure under thermal stress and remain above 80% of the original power conversion efficiency (PCE) after thermal aging at 85 oC for 720 h. Notably, the chemical interactions between heteroatoms of self-doped carbon nanosheets and the mobile lead ions can effectively alleviate lead leakage and avoid the potential impacts of device degradation on ecosystem. Ultimately, the Co(III)-CNS doped PSCs with enhanced thermal stability exhibit a champion PCE of 22.32%.

Synergistic Interfacial Effect of Ru/Co3O4 Heterojunctions for Boosting Overall Water Splitting.

Low-cost bifunctional electrocatalysts capable of efficiently driving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are needed for the growth of a green hydrogen economy. Herein, a Ru/Co3O4 heterojunction catalyst rich in oxygen vacancies (VO) and supported on carbon cloth (RCO-VO@CC) is prepared via a solid phase reaction (SPR) strategy. A RuO2/Co9S8@CC precursor (ROC@CC) is first prepared by loading Co9S8 nanosheets onto CC, following the addition of RuO2 nanoparticles (NPs). After the SPR process in an Ar atmosphere, Ru/Co3O4 heterojunctions with abundant VO are formed on the CC. The compositionally optimized RCO-VO@CC electrocatalyst with a Ru content of 0.55 wt.% exhibits very low overpotential values of 11 and 253 mV at 10 mA cm-2 for HER and OER, respectively, in 1 m KOH. Further, a low cell voltage of only 1.49 V is required to achieve a current density of 10 mA cm-2. Density functional theoretical calculations verify that the outstanding bifunctional electrocatalytic performance originates from synergistic charge transfer between Ru metal and VO-rich Co3O4. This work reports a novel approach toward a high-efficiency HER/OER electrocatalyst for energy storage and conversion.