Polymeric organic photovoltaic (OPV) cells are promising candidates for low-cost, high-performance energy sources due to their low material and processing costs, flexibility, and ease of manufacturing by solution processes. However, low power-conversion efficiency (PCE) has impeded the development of OPV cells. The low PCE in OPV solar cells has been attributed to low carrier mobility, which is related to the transport length of the charge carriers within active layers. Graphene can be an ideal material for assisting the charge transport in the active layer of OPV cells due to its excellent charger carrier mobility, thermal and chemical stability, and compatibility with the solution process. In this work, we demonstrated for the first time an improvement of the PCE (up to 40%) in OPV bulk-heterojunction (BHJ) cells by incorporating charge-selective graphene flakes into the BHJ active layer. The charge selectivity of graphene flakes was achieved by nitrogen doping (N-doped graphene). The N-doped graphene, when mixed in the active layer (N-doped graphene/polymer:fullerene composites), provided transport pathways exclusively to specific charge carriers through the modulation of band-gap structures. We discuss further the enhancement of the PCE in OPV cells with respect to charge-carrier mobility. Broader contextOrganic solar cells have received a lot of attention due to their low production costs, easy scalability to large-areas and applicability on exible substrates. One of the main challenges to widespread application in practical devices is their low power conversion efficiency (PCE). This is largely because of the low charge-carrier mobilities and poor charge transfer characteristics in organic materials, resulting in short carrier lifetimes and reduced charge collection efficiencies. In this work, we demonstrate that the use of nitrogen-doped graphene improves the power conversion efficiency of a bulk-heterojunction solar cell system. The nitrogen-doped graphene provides transport pathways to specic charge carriers through the modulation of band structures when mixed into the active layer. We believe that the added functionality of charge selectivity in conductive graphene akes gives a new design parameter for increasing the PCE of bulk-heterojunction solar cells.

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Energy-effective, ecofriendly desalination is a technology in universal demand due to global water scarcity. Capacitive deionization (CDI) is a promising method that has those advantages, but it is still necessary to enhance desalination performance to desalinate high-concentration raw salt water. In this work, carbon nanotubes (CNTs) are used as a conductive agent of the CDI electrode. To use CNTs as a conductive agent, we examine the effect of the dispersion status of the CNTs within activated carbon active material on the CDI performance. Acid treatment-functionalization of CNTs created a better dispersion status than CNTs without any treatment. Homogeneously dispersed CNTs showed enhanced electrochemical and desalination performance. Interestingly, desalination tests with highly concentrated raw salt water achieved a more notable improvement with 13.9% at only 1 wt % of CNT dispersion. The improvement mechanisms with dispersing CNTs such as increment of surface area and decrement of electrode resistivity are analyzed.

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