Tuning the work functions of graphene quantum dot-modified electrodes for polymer solar cell applications

Recent Progress in Carbon-Based Buffer Layers for Polymer Solar Cells

Carbon-based materials are promising candidates as charge transport layers in various optoelectronic devices and have been applied to enhance the performance and stability of such devices. In this paper, we provide an overview of the most contemporary strategies that use carbon-based materials including graphene, graphene oxide, carbon nanotubes, carbon quantum dots, and graphitic carbon nitride as buffer layers in polymer solar cells (PSCs). The crucial parameters that regulate the performance of carbon-based buffer layers are highlighted and discussed in detail. Furthermore, the performances of recently developed carbon-based materials as hole and electron transport layers in PSCs compared with those of commercially available hole/electron transport layers are evaluated. Finally, we elaborate on the remaining challenges and future directions for the development of carbon-based buffer layers to achieve high-efficiency and high-stability PSCs.

Hydrothermal Synthesis of Graphene Quantum Dots Supported on Three-Dimensional Graphene for Supercapacitors

Incorporation of new functional components into a three-dimensional graphene (3DG) framework improves the performance of supercapacitors based on 3DG as electrodes by tailoring the framework's structure and properties. In this work, graphene quantum dots (GQDs) were incorporated into 3DG via one-step hydrothermal treatment of GQDs and graphene oxide (GO). By simply adjusting the GQDs/GO feeding ratio by weight, various GQDs/3DG composites were formed. The maximum feeding ratio was 80%, and the prepared composites possessed saturated GQDs loading on the 3DG framework, whereas composites obtained with a GQDs/GO feeding ratio of 40% as electrodes exhibited optimal specific capacitance of 242 F·g-1 for supercapacitors, an increase of 22% compared with that of pure 3DG electrodes (198 F·g-1). This improved performance was mainly due to better electrical conductivity and larger surface area for GQDs/3DG composites with moderate GQDs content. The fabricated GQDs/3DG composites as electrodes for supercapacitors revealed high electrochemical stability. Their capacitance kept 93% of the initial value after 10,000 charge-discharge cycles.

Highly photoluminescent and temperature-sensitive P, N, B-co-doped carbon quantum dots and their highly sensitive recognition for curcumin

Temperature-sensitive P, N, B-co-doped carbon quantum dots (PNBCDs) synthesized using one-pot method exhibit many excellent features, such as strong fluorescence, good stability and sensitive detection for curcumin.

Design and adjustment of the graphene work function via size, modification, defects, and doping: a first-principle theory study

In this work, the work function (WF) of graphenes, which are used as electronic devices, has been designed and evaluated by using the first-principle approach. Different states of graphene were considered, such as surface modification, doping, and defects. Firstly, WF strongly depends on the width of pristine graphene. A bigger width leads to a smaller WF. In addition, the effects of hydroxyls, defects, and positions of hydroxyls and defects are of concern. The WF of the graphene which is modified with hydroxyls is bigger than that of the pristine graphene. Moreover, the WF value increases with the number of hydroxyls. Positions of the hydroxyls and defects that deviated from the center have limited influence on the WF, whereas the effect of the position in the center is substantial. Lastly, B, N, Al, Si, and P are chosen as the doping elements. The n-type graphene doped with N and P atoms results in a huge decline in the WF, whereas the p-type graphene doped with B and Al atoms causes a great increase in the WF. However, the doping of Al in graphene is difficult, whereas the doping of B and N is easier. These discoveries will provide heavy support for the production of graphene-based devices.

Oleylamine-functionalized graphene oxide as an electron block layer towards high-performance and photostable fullerene-free polymer solar cells

Oleylamine-functionalized graphene oxide (GO) has a shallower energy level of conduction band (E_CB) and a deeper energy level of the valence band (E_VB) as compared to common hole extraction layer (HEL) materials, which make the electron block layer (EBL). Photoluminescence, X-ray photoelectron spectroscopy (XPS), and current density-voltage (J-V) curves with a large reverse bias voltage range obtained under dark conditions are used to determine whether GO layers play important roles in blocking the electron transport to the MoO₃/Ag composite anode and prevent MoO₃ diffusion into a photoactive layer under light illumination. Moreover, GO inserted between a photoactive layer and an HEL enhances charge carrier transport and collection and avoids the monomolecular recombination between the photoactive layer and HEL. Photovoltaic parameters and photostability measurements of inverted and forward PSCs have shown that upon introduction of GO, the performance and photostability of PSCs are improved. On adding GO to PSCs, the power conversion efficiency (PCE) increases approximately 5% and 4% and reduces the decay ratio to approximately 50% and 65% of the initial value for the inverted and forward PSCs, respectively.