Recent advances in carbon-based materials for high-performance perovskite solar cells: gaps, challenges and fulfillment.

Presently, carbon-based nanomaterials have shown tremendous potential for energy conversion applications. Especially, carbon-based materials have emerged as excellent candidates for the fabrication of halide perovskite-based solar cells, which may lead to their commercialization. In the last decade, PSCs have rapidly developed, and these hybrid devices demonstrate a comparable performance to silicon-based solar cells in terms of power conversion efficiency (PCE). However, PSCs lag behind silicon-based solar cells due to their poor stability and durability. Generally, noble metals such gold and silver are employed as back electrode materials during the fabrication of PSCs. However, the use of these expensive rare metals is associated with some issues, urgently necessitating the search for cost-effective materials, which can realize the commercial applications of PSCs due to their interesting properties. Thus, the present review shows how carbon-based materials can become the main candidates for the development of highly efficient and stable PSCs. Carbon-based materials such as carbon black, graphite, graphene nanosheets (2D/3D), carbon nanotubes (CNTs), carbon dots, graphene quantum dots (GQDs) and carbon nanosheets show potential for the laboratory and large-scale fabrication of solar cells and modules. Carbon-based PSCs can achieve efficient and long-term stability for both rigid and flexible substrates because of their high conductivity and excellent hydrophobicity, thus showing good results in comparison to metal electrode-based PSCs. Thus, the present review also demonstrates and discusses the latest state-of-the-art and recent advances for carbon-based PSCs. Furthermore, we present perspectives on the cost-effective synthesis of carbon-based materials for the broader view of the future sustainability of carbon-based PSCs.

Vanadium pentaoxide-doped waste plastic-derived graphene nanocomposite for supercapacitors: a comparative electrochemical study of low and high metal oxide doping.

We report the bulk phase synthesis of graphene sheets using waste plastic (WP) as a precursor following a modified pyrolysis approach. Furthermore, the low and high mass loading of vanadium pentaoxide was performed on graphene sheets in 1 : 10 and 1 : 1 ratios, respectively. Advanced characterization techniques such as Raman spectroscopy, FT-IR spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA) analysis, and SEM imaging were used to confirm the synthesis of graphene. FT-IR spectroscopy confirmed that the resonating structure affects the bond strength in the composite, which enables peak shifting in the FT-IR spectrum of the composite. Furthermore, bandgap analysis has been performed using UV-Vis spectroscopy, which confirmed the synthesis of the composites. The developed vanadium-doped graphene was used as the active material for the fabrication of supercapacitor electrodes. The electrochemical performance of these devices was evaluated in 1 M H3PO4 solution using cyclic voltammetry (CV), galvanic charge-discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS). Fabricated cells 1 and 2 showed exceptional specific capacitances of 139.7 F g-1 and 51.2 F g-1 at 5 mV s-1 scan rate, respectively. Cell 1 showed a huge power density of 5312 W kg-1 and an energy density of 19.7 W h kg-1. Conversely, cell 2 showed a comparatively lower power density of 1941 W kg-1 and an energy density of 7.2 W h kg-1 at a 5 mV s-1 scan rate. Moreover, we disclose some brief conclusions on the performance, mechanism, and required modifications that can improve the performance of such devices. This approach can surely help with universal WP problems as well as the development of high-performance supercapacitors.

Graphene nanosheets derived from plastic waste for the application of DSSCs and supercapacitors.

The present study reports the upcycling process of waste plastics into value-added product graphene nanosheets (GNs) and their subsequent applications in dye sensitized solar cells (DSSCs) and supercapacitors. Bentonite nanoclay has been used as an agent for the degradation of waste plastics with two step pyrolysis processes at 450 °C and 945 °C in an inert atmosphere of N2 gas to obtain GNs. The GNs with few layers were confirmed by the RAMAN spectroscopy, XRD and HRTEM analyses. Further, FT-IR and EDX analyses also performed for the identification and quantitative analysis of functional groups in GNs. The GNs thus synthesized from plastic waste have been used for the fabrication of DSSCs and supercapacitors. The DSSC fabrication with GNs as part of photo-anode with polymeric electrolyte showed a high fill factor of 86.4% and high Voc of 0.77 V, which were also supported by the computational findings. On the other hand, the utilization of GNs as an active layer material of supercapacitor electrodes offered a high specific capacitance of 398 F/g with a scan rate of 0.005 V/s. The supercapacitor also exhibited significant energy density (Ed) and power density (Pd) of 38 Wh/kg and 1009.74 W/kg, respectively. Thus, the process illustrated the utility of waste plastics upcycling for conservation of EEE i.e., ecology, economy and energy for better tomorrow.

3D graphene nanosheets from plastic waste for highly efficient HTM free perovskite solar cells.

Herein, we report the first time application of waste plastic derived 3D graphene nanosheets (GNs) for hole transport material (HTM) free perovskite solar cells (PSCs), where 3D GNs have been employed as an electrode dopant material in monolithic carbon electrode based mesoscopic PSCs. Waste plastics were upcycled into high-quality 3D GNs by using two-step pyrolysis processes, where, a nickel (99.99%) metal mesh was taken as the catalytic and degradation template to get an acid free route for the synthesis of 3D GNs. Raman spectroscopy, HRTEM analysis and XRD analysis show the presence of 1-2 graphene layers within the 3D GNs. Further, the optical band gap study has also been performed to analyze the applicability of 3D GNs for PSCs. The optimized device with 3D GNs shows a power conversion efficiency (PCE) of 12.40%, whereas the carbon-based control device shows a PCE of 11.04%. Further, all other device parameters such as short circuit current (J sc), open circuit voltage (V oc) and fill factor (FF) have been improved with the addition of 3D GNs. The performance enhancement in 3D GN doped HTM free PSC solar cells is attributed to the enhancement in conductivity and reduced recombination within the device. Further, the photocurrent study shows that the 3D GN device shows better performance as compared to the reference device due to the larger diffusion current. Thus, the upcycling of waste plastics into 3D GNs and their exploitation for application in energy conversion show an effective and potential way to convert waste into energy.

Mass production of metal-doped graphene from the agriculture waste of Quercus ilex leaves for supercapacitors: inclusive DFT study.

This work reports a facile, eco-friendly, and cost-effective mass-scale synthesis of metal-doped graphene sheets (MDGs) using agriculture waste of Quercus ilex leaves for supercapacitor applications. A single step-degradation catalyst-based pyrolysis route was used for the manufacture of MDGs. Obtained MDGs were further evaluated via advanced spectroscopy and microscopic techniques including Raman spectroscopy, FT-IR, XRD, SEM/EDX, and TEM imaging. The Raman spectrum showed D and G bands at 1300 cm-1 and 1590 cm-1, respectively, followed by a 2D band at 2770 cm-1, which confirmed the synthesis of few-layered MDGs. The SEM/EDX data confirmed the presence of 6.15%, 3.17%, and 2.36% of potassium, calcium and magnesium in the obtained MDGs, respectively. Additionally, the FT-IR, XRD, TEM, and SEM data including the plot profile diagrams confirmed the synthesis of MDGs. Further, a computational study was performed for the structural validation of MDGs using Gaussian 09. The density functional theory (DFT) results showed a chemisorption/decoration pattern of doping for metal ions on the few-layered graphene nanosheets, rather than a substitutional pattern. Further, resulting MDGs were used as an active material for the fabrication of a supercapacitor electrode using the polymer gel of PVA-H3PO4 as the electrolyte. The fabricated device showed a decent specific capacitance of 18.2 F g-1 at a scan rate of 5 mV s-1 with a power density of 1000 W kg-1 at 5 A g-1.

Single Step Blending of PEDOT:PSS/SPGO Nanocomposite via Low Temperature Solid Phase Addition of Graphene Oxide for Effective Hole Transport Layer in Organic Solar Cells.

Herein, we report the modification of PEDOT:PSS by in-situ direct addition of graphene oxide powder processed by spray dryer (SPGO) for the enhancement in the performance of organic solar cell. The preparation of PEDOT:PSS/SPGO composite was done by direct incorporation of graphene oxide powder at lower temperature i.e., below 5 °C. Raman spectroscopy of the prepared PEDOT:PSS/SPGO nanocomposites at low temperature suggested that low temperature plays a vital role to improve the ability of these composite as hole transport layer by improving adhesive properties of the composite. Atomic force microscopy (AFM) analysis suggested that the adhesive ability of these composite decreased surface roughness and thus providing smoother path for the hole transportation. After the successful synthesis of PEDOT:PSS/SPGO nanocomposites, ITO/PEDOT:PSS/SPGO/PTB7:PC71BM/Al based organic solar cell was fabricated. The J-V curves under AM 1.5G illumination (100 mW/cm²) of the PTB7:PC71BM based OSCs using PEDOT:PSS/SPGO as a HTL exhibit Voc = 0.67 V, Jsc = 17.3 mA, FF = 41.5%, PCE = 4.82%, and device with PEDOT:PSS as HTL exhibit Voc = 0.68 V, Jsc = 16.0 mA/cm², FF = 38.7% and PCE = 4.04%. The enhance PCE in case of PEDOT:PSS/SPGO based devices depicted that the direct inclusion of graphene oxide in PEDOT:PSS increased the PCE almost 16%, which arises due the high conductivity and stable pi-pi stacking of the spray dryer processed graphene sheets with PEDOT:PSS which ease the charge carrier mobility, thus providing feasible path for charge transportation.

A simple, eco-friendly and green approach to synthesis of blue photoluminescent potassium-doped graphene oxide from agriculture waste for bio-imaging applications.

2D carbon nanomaterials such as graphene and its oxide counterpart have sought good research attention for their application as well as fundamental interest. Especially the versatility of graphene oxide establishes its elite candidature in every field because of diverse application potential. Here we are reporting a greener, eco-friendly and cost effective one step hydrothermal route for the synthesis of potassium doped graphene oxide (K-doped GO) from agricultural waste i.e. Quercus ilex Fruit. The elemental analysis and XPS study showed the high percentage (6.81%) of natural doping of potassium. The K-doped GO is specific and demonstrates bright blue photoluminescence (PL) under UV-light (λex = 365 nm). Low toxicity, intracellular localization, good biocompatibility and strong PL properties of the synthesized K-doped GOs portray it as an excellent bio-imaging agent holding great promise in analytical and biological fields.

Bulk synthesis of graphene nanosheets from plastic waste: An invincible method of solid waste management for better tomorrow.

Waste plastic management and converting it into value added products is one of the greatest challenges before the scientific community. The present work reports a cost effective, environment friendly and mass production capable method for upcycling of solid plastic waste into value added product (graphene). A two step pyrolysis processes i.e. firstly at 400 °C in presence of nanoclay followed by at 750 °C under nitrogen atmosphere was performed to obtain a black charged residue. Raman spectroscopy was performed on the obtained residue, where the observed D and G bands at 1342 cm-1 and 1594 cm-1, respectively, confirm the synthesis of graphene nano sheets. In addition, a broad 2D band at 2790 cm-1 confirm the presence of few layer graphene nano sheets. The obtained graphene nanosheets were also confirmed through the computational data by Gaussian09, where the peaks at 1379 cm-1 and 1596 cm-1 for D and G band, respectively, make a good agreement with experimental data. TEM, FT-IR and EDX spectroscopy were also performed to confirm the synthesis of graphene nanosheets including the functional group identification and quantitative analysis for elements, respectively.