The field of invention describes a process of manufacturing of for the Mass production of graphene nanosheets (GNs) for energy application.
BACKGROUND OF THE INVENTION

Recently, carbon nanomaterials have taken significant interest over the past few decades due to their promising electrical and optical properties for various optoelectronic applications [1]. In the regard, graphene as the 2-D analog among carbon nanomaterials, has shown tremendous interest for the application of photovoltaics due its extraordinary electrical and optical properties [2-5]. Graphene is regarded as one of the versatile and universal wonder material that could be utilized for the improvement in the device parameters of the solar cells [6-10]. Among the generations of the solar cells, third generation solar cells have shown most promising cost effective routes for the fabrication of solar cells. In this regard, remarkable work has been done in the last few years back, where these third generation solar cells has depicted solution processable techniques for the fabrication of large area solar cells. Among third generation, organic solar cells (OPVs) dye sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) showed remarkable interest due to their cost effectiveness and ease of fabrication routes. However these solar cells still lagging behind the traditional silicon based solar cells in terms of stability and power conversion efficiency both [11-14]. In this regard, several new materials have been developed in order to make a significant improvement in PCEs and stability of these solar cells. Graphene is one of such kind of materials, which is widely used in these solar cells to improve the device parameters especially PCEs and stability. It could be used as hole transport layer in OPVs and PSCs, while it is used as band tuner or active electrode material in dye-sensitized solar cells [15-18]. Recently, modular architecture based design was also introduced for graphene based PSCs by Zang et. al. , in which high efficiency and stability were recorded by using graphene nanosheets in two different subcells to get a single subcell. R.Bhakrari et. al. showed the effect graphene content as dopant in P3HT: graphene based solar cells and showed that PCEs of the solar cell depends upon the doping level of the graphene in P3HT [20]. S.Jung et al reported the high performance graphene based organic solar cells for the improvement of interface control in PTB7:PC71BM based organic solar cells and achieved nearly a PCE of 8.38% for inverted structure. This study showed the effect of polar solvent for to cover the charge transporting layers completely by graphene [21]. Further, due to the excellent electrical properties of the graphene, transparent conducting electrodes of graphene were also investigated to enhance the properties of OPVs. H.Park et al investigated role of graphene as candidate of TCEs in OPVs and showed comparable device parameters with that of ITO based OPVs. However, the study shown by this group also showed the doping effect for the best performance of the graphene as transparent electrodes and HTL in OPVs. [22] Generally, PEDOT:PSS based HTLs are employed in the OPVs, however, due to hygroscopic nature of the PEDOT:PSS, it has been observed that active layer of the OPVs gets degraded with time, which reduces the overall the performance of the OPVs with time. In this regard, graphene oxide can be used as modifier to enhance the properties of the PEDOT: PSS. Recently, we also reported the utility of spray dryer processed graphene oxide (SPGO) in PEDOT: PSS to enhance the properties of PTB7:PC71BM based OPVs [23]. Further, it have been reported that graphene could be used as a band tuner and counter electrode material in DSSCs. [24-26]. Recently, graphene based large area DSSCs was introduced by, S.Casaluci et al. This group spray coated the graphene sheets over the transparent conducting electrode to replace the platinum based counter electrode and achieved 3.5% PCE for an active area of 43.2 cm2 [27]. The possibility of adaptation of graphene in perovskite solar cell was also demonstrated in several studies [28]. The role of graphene as electron transport material (ETL) was reported by F.Biccari et al. in perovskite solar cells to achieve high carrier injection, where mesoporous TiO2 layer was doped with graphene. It is found that by adding graphene, the charge collection efficiency was improved by two fold [29]. Thus, these studies on the utility of the graphene in third generation solar cells showed that graphene could become one of the potential materials for the development of third generation solar cells. However, still the production of the cost effective high quality graphene nanosheets is still demanded by researchers for the wide scale of the graphene nanosheets for the photovoltaic applications. Till date, several synthesis routes have been identified in order to make high quality graphene nanosheets, which includes the synthesis of the graphene via chemical method, chemical vapour deposition method, scotch tape method, mechanical exfoliations, physical vapour deposition, microwave assisted exfoliation, electrochemical exfoliation and so on [30-35]. However, none of these methods are shown significant interest for the mass scale production to solve the problem of the cost benefit analysis. Recently, interest have been developed in carbon containing waste materials, which could effectively used as precursor materials for the synthesis of the graphene nanosheets [36-40]. The category of the carbon containing waste materials generally employed the synthesis of graphene nanosheets includes plastic waste, agriculture waste, biomass and paper waste. Recently various researchers showed the synthesis of the graphene nanosheets from plastic waste. In this regard, recently we have reported the bulk production of the graphene nanosheets from plastic waste by using nanoclay as degradation agent [41]. While several other researchers showed the synthesis of carbon spheres, carbon nanotubes, carbon nanofibers, graphene nanosheets and carbon nanosheets by using different kinds of catalytic media for the growth of the graphene nanosheets. However, a very little research has yet now being done from paper waste, which could become an effective source for the mass production of the graphene nanosheets.
Therefore, in the present work, we report a very facile and eco-friendly technique for the mass production of the graphene nanosheets from paper waste. The production of the graphene nanosheets was done by using two stage pyrolytic techniques in the temperature range of the 400°-950°C by using ethyl alcohol as aromatic carbon developer. Further, few layer graphene nanosheets thus obtained from paper waste were also exploited in the third generation solar cells including OPVs, DSSCs and PSCs to improve the parameters of the these solar cells as evaluated for the study of optical band gap. Further, supercapacitors were also fabricated by using these GNs, which depicted the utility of these GNs for energy storage applications. Thus overall results showed that incorporation of naturally doped Si, Mg and Ca GNs for energy applications.

The present stare of art showed the first time approach for the mass scale production of Si, Mg and Ca doped GNs for the energy applications. The previous state of art showed the synthesis of GNs from other sources by using various catalytic medium and doping were done after the synthesis of the GNs, while some of them showed the synthesis of GNs by using chemical techniques which used toxic chemicals. While the present synthesis route showed a completely eco-friendly technique for without taking any catalytic system. Further, the present system utilized a definite ratio of methanol and ethanol for the synthesis. The naturally doped system makes it suitable for the various energy applications, which again makes it unique process for the mass scale production. Characterization of the thus obtained GNs showed the presence of few layer doped GNs. The list of references referred herein are provided below:
References:
[1] Jariwala, D., Sangwan, V.K., Lauhon, L.J., Marks, T.J. and Hersam, M.C., 2013. Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing. Chemical Society Reviews, 42(7), pp.2824-2860.
[2] Dai, L., Chang, D.W., Baek, J.B. and Lu, W., 2012. Carbon nanomaterials for advanced energy conversion and storage. small, 8(8), pp.1130-1166.
[3] Brennan, L.J., Byrne, M.T., Bari, M. and Gun'ko, Y.K., 2011. Carbon nanomaterials for dye-sensitized solar cell applications: a bright future. Advanced Energy Materials, 1(4), pp.472-485.
[4] Brennan, L.J., Byrne, M.T., Bari, M. and Gun'ko, Y.K., 2011. Carbon nanomaterials for dye-sensitized solar cell applications: a bright future. Advanced Energy Materials, 1(4), pp.472-485.
[5] Kim, T.H., Yang, S.J. and Park, C.R., 2011. Carbon nanomaterials in organic photovoltaic cells. Carbon letters, 12(4), pp.194-206.
[6] Geim, A.K. and Novoselov, K.S., 2010. The rise of graphene. In Nanoscience and technology: a collection of reviews from nature journals (pp. 11-19).
[7] Xing, G., Guo, H., Zhang, X., Sum, T.C. and Huan, C.H.A., 2010. The physics of ultrafast saturable absorption in graphene. Optics express, 18(5), pp.4564-4573.
[8] Konios, D., Petridis, C., Kakavelakis, G., Sygletou, M., Savva, K., Stratakis, E. and Kymakis, E., 2015. Reduced graphene oxide micromesh electrodes for large area, flexible, organic photovoltaic devices. Advanced Functional Materials, 25(15), pp.2213-2221.
[9] Zhang, X., Rajaraman, B.R., Liu, H. and Ramakrishna, S., 2014. Graphene's potential in materials science and engineering. RSC Advances, 4(55), pp.28987-29011.
[10] Zhang, Y.I., Zhang, L. and Zhou, C., 2013. Review of chemical vapor deposition of graphene and related applications. Accounts of chemical research, 46(10), pp.2329-2339.
[11] Yan, J. and Saunders, B.R., 2014. Third-generation solar cells: a review and comparison of polymer: fullerene, hybrid polymer and perovskite solar cells. Rsc Advances, 4(82), pp.43286-43314.
[12] Girtan, M., 2012. Comparison of ITO/metal/ITO and ZnO/metal/ZnO characteristics as transparent electrodes for third generation solar cells. Solar Energy Materials and Solar Cells, 100, pp.153-161.
[13] Green, M.A., 2002. Third generation photovoltaics: solar cells for 2020 and beyond. Physica E: Low-dimensional Systems and Nanostructures, 14(1-2), pp.65-70.
[14] Algora, C., 2003. The importance of the very high concentration in third-generation solar cells. In Next generation photovoltaics (pp. 120-151). CRC Press.
[15] Sahoo, N.G., Pan, Y., Li, L. and Chan, S.H., 2012. Graphene-based materials for energy conversion. Advanced Materials, 24(30), pp.4203-4210.
[16] Iwan, A. and Chuchmala, A., 2012. Perspectives of applied graphene: Polymer solar cells. Progress in Polymer Science, 37(12), pp.1805-1828.
[17] Singh, E. and Nalwa, H.S., 2015. Graphene-based bulk-heterojunction solar cells: a review. Journal of nanoscience and nanotechnology, 15(9), pp.6237-6278.
[18] Singh, E. and Nalwa, H.S., 2015. Graphene-based dye-sensitized solar cells: a review. Science of advanced Materials, 7(10), pp.1863-1912.
[20] Bkakri, R., Chehata, N., Ltaief, A., Kusmartseva, O.E., Kusmartsev, F.V., Song, M. and Bouazizi, A., 2015. Effects of the graphene content on the conversion efficiency of P3HT: Graphene based organic solar cells. Journal of Physics and Chemistry of Solids, 85, pp.206-211
[21] Jung, S., Lee, J., Choi, Y., Lee, S.M., Yang, C. and Park, H., 2017. Improved interface control for high-performance graphene-based organic solar cells. 2D Materials, 4(4), p.045004.
[22] Park, H., Rowehl, J.A., Kim, K.K., Bulovic, V. and Kong, J., 2010. Doped graphene electrodes for organic solar cells. Nanotechnology, 21(50), p.505204.
[23] Pandey, S., Karakoti, M., Chaudhary, N., Gupta, S., Kumar, A., Dhali, S., Patra, A., Singh, R.K. and Sahoo, N.G., 2020. 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. Journal of nanoscience and nanotechnology, 20(6), pp.3888-3895.
[24] Zhang, D.W., Li, X.D., Li, H.B., Chen, S., Sun, Z., Yin, X.J. and Huang, S.M., 2011. Graphene-based counter electrode for dye-sensitized solar cells. Carbon, 49(15), pp.5382-5388.
[25] Singh, E. and Nalwa, H.S., 2015. Graphene-based dye-sensitized solar cells: a review. Science of advanced Materials, 7(10), pp.1863-1912.
[26] Wang, H. and Hu, Y.H., 2012. Graphene as a counter electrode material for dye-sensitized solar cells. Energy & Environmental Science, 5(8), pp.8182-8188
[27] Casaluci, S., Gemmi, M., Pellegrini, V., Di Carlo, A. and Bonaccorso, F., 2016. Graphene-based large area dye-sensitized solar cell modules. Nanoscale, 8(9), pp.5368-5378.
[28] Lim, E.L., Yap, C.C., Jumali, M.H.H., Teridi, M.A.M. and Teh, C.H., 2018. A mini review: Can graphene be a novel material for perovskite solar cell applications?. Nano-micro letters, 10(2), p.27.
[29] Biccari, F., Gabelloni, F., Burzi, E., Gurioli, M., Pescetelli, S., Agresti, A., Del Rio Castillo, A.E., Ansaldo, A., Kymakis, E., Bonaccorso, F. and Di Carlo, A., 2017. Graphene-Based Electron Transport Layers in Perovskite Solar Cells: A Step-Up for an Efficient Carrier Collection. Advanced Energy Materials, 7(22), p.1701349.
[30] Choi, W., Lahiri, I., Seelaboyina, R. and Kang, Y.S., 2010. Synthesis of graphene and its applications: a review. Critical Reviews in Solid State and Materials Sciences, 35(1), pp.52-71.
[31] Toh, S.Y., Loh, K.S., Kamarudin, S.K. and Daud, W.R.W., 2014. Graphene production via electrochemical reduction of graphene oxide: synthesis and characterisation. Chemical Engineering Journal, 251, pp.422-434.
[32] Acik, M. and Chabal, Y.J., 2013. A review on thermal exfoliation of graphene oxide. Journal of Materials Science Research, 2(1), p.101.
[33] Rafique, M.M.A. and Iqbal, J., 2011. Production of carbon nanotubes by different routes-a review. Journal of encapsulation and adsorption sciences, 1(02), p.29.
[34] Jia, X., Campos-Delgado, J., Terrones, M., Meunier, V. and Dresselhaus, M.S., 2011. Graphene edges: a review of their fabrication and characterization. Nanoscale, 3(1), pp.86-95.
[35] Lee, X.J., Hiew, B.Y.Z., Lai, K.C., Lee, L.Y., Gan, S., Thangalazhy-Gopakumar, S. and Rigby, S., 2019. Review on graphene and its derivatives: Synthesis methods and potential industrial implementation. Journal of the Taiwan Institute of Chemical Engineers, 98, pp.163-180.
[36] Zhuo, C. and Levendis, Y.A., 2014. Upcycling waste plastics into carbon nanomaterials: A review. Journal of Applied Polymer Science, 131(4).
[37] Kumar, R., Singh, R.K. and Singh, D.P., 2016. Natural and waste hydrocarbon precursors for the synthesis of carbon based nanomaterials: graphene and CNTs. Renewable and Sustainable Energy Reviews, 58, pp.976-1006.
[38] Zahid, M.U., Pervaiz, E., Hussain, A., Shahzad, M.I. and Niazi, M.B.K., 2018. Synthesis of carbon nanomaterials from different pyrolysis techniques: a review. Materials Research Express, 5(5), p.052002.
[39] Mukherjee, A., Majumdar, S., Servin, A.D., Pagano, L., Dhankher, O.P. and White, J.C., 2016. Carbon nanomaterials in agriculture: a critical review. Frontiers in plant science, 7, p.172.
[40] Tewari, C., Tatrari, G., Karakoti, M., Pandey, S., Pal, M., Rana, S., SanthiBhushan, B., Melkani, A.B., Srivastava, A. and Sahoo, N.G., 2019. A simple, eco-friendly and green approach to synthesis of blue photoluminescent potassium-doped graphene oxide from agriculture waste for bio-imaging applications. Materials Science and Engineering: C, 104, p.109970.
[41] Pandey, S., Karakoti, M., Dhali, S., Karki, N., SanthiBhushan, B., Tewari, C., Rana, S., Srivastava, A., Melkani, A.B. and Sahoo, N.G., 2019. Bulk synthesis of graphene nanosheets from plastic waste: An invincible method of solid waste management for better tomorrow. Waste management, 88, pp.48-55.
[42] Khan, Q.A., Shaur, A., Khan, T.A., Joya, Y.F., Awan, M.S., 2017. Characterization of reduced graphene oxide produced through a modified Hoffman method. Cogent Chem. 3, 1298980.
[43] Chen, X., Chen, B., 2015. Macroscopic and spectroscopic investigations of the adsorption of nitroaromatic compounds on graphene oxide, reduced graphene oxide, and graphene nanosheets. Environ. Sci. Technol. 49, 6181–6189.
[44] Ferrari, A., & Robertson, J. (2000). Interpretation of Raman spectra of disordered and amorphous carbon. Physical Review B, 61, 14095–14107. http://dx.doi.org/10.1103/PhysRevB.61.14095
[45] Shen, Y., & Lua, A. C. (2013). A facile method for the large-scale continuous synthesis of graphene sheets using a novel catalyst. Scientific Reports, 3, 1–6
[46] Choi, W.S., Hong, S.H.B., Lim, D.G., Yang, K.J., Lee, J.H., 2006. Effect of hydrogen plasma pretreatment on growth of carbon nanotubes by MPECVD. Mater. Sci. Eng. C. 26, 1211.
[47] Karmakar, B. (2016). Fundamentals of Glass and Glass Nanocomposites. Glass Nanocomposites, 3–53. doi:10.1016/b978-0-323-39309-6.00001-8 (https://doi.org/10.1016/b978-0-323-39309-6.00001-8)
[48] N. R. Wilson, P. A. Pandey, R. Beanland, R. J. Young, I. A. Kinloch, L. Gong, Z. Liu, K. Suenaga, J. P. Rourke, S. J. York, J. Sloan, ACS Nano., 3, 2547 (2009).

[49] Krishnamoorthy, K., Veerapandian, M., Kim, G.S., Jae Kim, S., 2012. A one step hydrothermal approach for the improved synthesis of graphene nanosheets. Curr. Nanosci. 8, 934–938

SUMMARY OF THE INVENTION

The field of invention describes a process of manufacturing of naturally doped graphene nanosheets (GNs) from paper waste. The synthesis of the graphene nanosheets from waste papers was done in two stage pyrolysis process. The process utilizes a definite ratio of methanol and ethanol to enhance the molecular trapping of the charges and channelized charge transportation for the application of energy conversion and storage.
Herewith, we report the mass scale production of few layer graphene nanosheets from paper waste doped with naturally available silicon and calcium for the application of the third generation solar cells. The growth of the graphene nanosheets from waste plastic were done in two stage pyrolytic process, where ethyl alcohol was taken as the skeleton developer for the formation of aromatic carbons atoms. Raman spectroscopy clearly showed the synthesis of the few layer graphene nanosheets from paper waste, which is further supported by HRTEM images and XRD graph. The EDX spectrum of paper waste derived graphene nanosheets showed the presence of silicon (Si), magnesium (Mg) and calcium (Ca) within the graphene nanosheets. Because of the presence of these metals within these graphene nanosheets, third generation solar cells could be fabricated such as organic solar cell, perovskite solar cell and dye sensitized solar cells to improve the device parameters as shown by obtained optical band gap (2.25 eV) of the GNs. Further, the fabrication of supercapacitors from these metal doped GNs showed that potential application of GNs for energy conversion and storage applications.
In an embodiment, the process of manufacturing graphene nanosheet from paper waste, comprises stirring a mixture containing distilled water and about 8kg to 12kg of paper waste for about 1 minute to 3 minutes. The process further comprises filtering the mixture using a filtration net and washing the residue obtained. Then, soaking the residue for about 20 minutes to about 40 minutes in a first mixture containing methanol, ethanol and distilled water in a ratio of 2:3:25. Then, heating the residue and the first mixture together for about 20 minutes to about 40 minutes at a temperature ranging from 50°C to 70°C and obtaining a slurry mixture by removing the residue from the first mixture and rinsing the residue. The process further comprises performing a first pyrolysis method on the slurry mixture at a temperature ranging from 300°C to 400°C under an inert atmosphere and obtaining amorphous carbon as product of the first pyrolysis method. Then, ball milling the amorphous carbon to obtain an ultrafine powder and performing a second pyrolysis method on the ultrafine powder at a temperature ranging from 850°C to 950°C. Lastly, obtaining graphene nanosheet as product of the second pyrolysis method.
The embodiment of the present work showed the utility of pyrolysis techniques to develop scalable and green synthesis of naturally doped GNs with Si, Mg and Ca.
Another embodiment of the work showed naturally doped graphene nanosheets (GNs) for Photovoltaic applications.
Additionally, the work showed the applicability of the GNs for energy storage applications.
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 shows a flowchart for the process of manufacturing graphene nanosheet from paper waste;
Figure 2 shows Raman spectrum of the paper waste derived graphene nanosheets;
Figure 3 shows FT-IR spectra synthesized graphene nanosheets;
Figure 4 shows XRD spectrum of the graphene nanosheets;
Figure 5 (a-d) shows FESEM images of graphene nanosheets;
Figure 6 (a-f) shows TEM images of the graphene nanosheets;
Figure 7 shows UV-visible spectroscopy of the paper waste grapheme;
Figure 8 shows Optical band gap of paper waste derived graphene nanosheets;
Figure 9 shows Cyclic voltammetry analysis of WP-G (a) Cell-1- With 1M H3PO4 electrolyte and (b) Cell- 2-With PVA-H3PO4 polymer gel electrolyte;
Figure 10 shows EIS analysis of WP-G (a) Cell-1- With 1M H3PO4 electrolyte and (b) Cell- 2-With PVA-H3PO4 polymer gel electrolyte; and
Figure 11 shows GCD analysis of WP-G (a) Cell-1- With 1M H3PO4 electrolyte and (b) Cell- 2-With PVA-H3PO4 polymer gel electrolyte.
Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale.

DETAILED DESCRIPTION:

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof. Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

Recently, carbon nanomaterials have taken significant interest over the past few decades due to their promising electrical and optical properties for various optoelectronic applications [1]. In the regard, graphene as the 2-D analog among carbon nanomaterials, has shown tremendous interest for the application of photovoltaics due its extraordinary electrical and optical properties [2-5]. Graphene is regarded as one of the versatile and universal wonder material that could be utilized for the improvement in the device parameters of the solar cells [6-10]. Among the generations of the solar cells, third generation solar cells have shown most promising cost effective routes for the fabrication of solar cells. In this regard, remarkable work has been done in the last few years back, where these third generation solar cells has depicted solution processable techniques for the fabrication of large area solar cells. Among third generation, organic solar cells (OPVs) dye sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) showed remarkable interest due to their cost effectiveness and ease of fabrication routes. However these solar cells still lagging behind the traditional silicon based solar cells in terms of stability and power conversion efficiency both [11-14]. In this regard, several new materials have been developed in order to make a significant improvement in PCEs and stability of these solar cells. Graphene is one of such kind of materials, which is widely used in these solar cells to improve the device parameters especially PCEs and stability. It could be used as hole transport layer in OPVs and PSCs, while it is used as band tuner or active electrode material in dye-sensitized solar cells [15-18]. Recently, modular architecture based design was also introduced for graphene based PSCs by Zang et. al. , in which high efficiency and stability were recorded by using graphene nanosheets in two different subcells to get a single subcell. R.Bhakrari et. al. showed the effect graphene content as dopant in P3HT: graphene based solar cells and showed that PCEs of the solar cell depends upon the doping level of the graphene in P3HT [20]. S.Jung et al reported the high performance graphene based organic solar cells for the improvement of interface control in PTB7:PC71BM based organic solar cells and achieved nearly a PCE of 8.38% for inverted structure. This study showed the effect of polar solvent for to cover the charge transporting layers completely by graphene [21]. Further, due to the excellent electrical properties of the graphene, transparent conducting electrodes of graphene were also investigated to enhance the properties of OPVs. H.Park et al investigated role of graphene as candidate of TCEs in OPVs and showed comparable device parameters with that of ITO based OPVs. However, the study shown by this group also showed the doping effect for the best performance of the graphene as transparent electrodes and HTL in OPVs. [22] Generally, PEDOT:PSS based HTLs are employed in the OPVs, however, due to hygroscopic nature of the PEDOT:PSS, it has been observed that active layer of the OPVs gets degraded with time, which reduces the overall the performance of the OPVs with time. In this regard, graphene oxide can be used as modifier to enhance the properties of the PEDOT: PSS. Recently, we also reported the utility of spray dryer processed graphene oxide (SPGO) in PEDOT: PSS to enhance the properties of PTB7:PC71BM based OPVs [23]. Further, it have been reported that graphene could be used as a band tuner and counter electrode material in DSSCs. [24-26]. Recently, graphene based large area DSSCs was introduced by, S.Casaluci et al. This group spray coated the graphene sheets over the transparent conducting electrode to replace the platinum based counter electrode and achieved 3.5% PCE for an active area of 43.2 cm2 [27]. The possibility of adaptation of graphene in perovskite solar cell was also demonstrated in several studies [28]. The role of graphene as electron transport material (ETL) was reported by F.Biccari et al. in perovskite solar cells to achieve high carrier injection, where mesoporous TiO2 layer was doped with graphene. It is found that by adding graphene, the charge collection efficiency was improved by two fold [29]. Thus, these studies on the utility of the graphene in third generation solar cells showed that graphene could become one of the potential materials for the development of third generation solar cells. However, still the production of the cost effective high quality graphene nanosheets is still demanded by researchers for the wide scale of the graphene nanosheets for the photovoltaic applications. Till date, several synthesis routes have been identified in order to make high quality graphene nanosheets, which includes the synthesis of the graphene via chemical method, chemical vapour deposition method, scotch tape method, mechanical exfoliations, physical vapour deposition, microwave assisted exfoliation, electrochemical exfoliation and so on [30-35]. However, none of these methods are shown significant interest for the mass scale production to solve the problem of the cost benefit analysis. Recently, interest have been developed in carbon containing waste materials, which could effectively used as precursor materials for the synthesis of the graphene nanosheets [36-40]. The category of the carbon containing waste materials generally employed the synthesis of graphene nanosheets includes plastic waste, agriculture waste, biomass and paper waste. Recently various researchers showed the synthesis of the graphene nanosheets from plastic waste. In this regard, recently we have reported the bulk production of the graphene nanosheets from plastic waste by using nanoclay as degradation agent [41]. While several other researchers showed the synthesis of carbon spheres, carbon nanotubes, carbon nanofibers, graphene nanosheets and carbon nanosheets by using different kinds of catalytic media for the growth of the graphene nanosheets. However, a very little research has yet now being done from paper waste, which could become an effective source for the mass production of the graphene nanosheets. Therefore, in the present work, we report a very facile and eco-friendly technique for the mass production of the graphene nanosheets from paper waste. The production of the graphene nanosheets was done by using two stage pyrolytic techniques in the temperature range of the 400°-950°C by using ethyl alcohol as aromatic carbon developer. Further, few layer graphene nanosheets thus obtained from paper waste were also exploited in the third generation solar cells including OPVs, DSSCs and PSCs to improve the parameters of the these solar cells. Results showed that incorporation of naturally doped bimetallic (Si and Ca) graphene nanosheets significantly improved the device parameters.
Materials and Method
The methodology for the production of naturally bimetal doped silicon and calcium doped graphene nanosheets includes several steps, which started from the collection of the 10kg of the waste paper (Century, A4 paper sheets) from local market and college offices. The waste paper thus collected then cutted into fine shape (11.2 mm length and 5.75 mm width) by using shredder unit. The shredded flakes of the waste paper then soaked into the distilled water and stirred for 2 min using a vertically aligned stirrer in order to remove dust and other impurities, which were then lifted up manually by using a filtration net with a pore size of 500µm. After that, the soaked and washed paper flakes again soaked for another 30 min in the mixture of methanol (200ml), ethanol (300ml) and distilled water (2.5 litres) and heated gently for 30 min at the temperature of 60°C. Then, the obtained dense slurry of the solvent mixed paper were gently rinsed and has undergone for the slow pyrolysis reactor made up of stainless steel with the capacity of the 0.41 m3 in the inert atmosphere of N2 gas (20 ml/min) at the temperature of 350°C with the heating rate of 5°C per min for 70 min. During the slow pyrolysis, backbone for the generation of aromatic carbon nanosheets was occurred through carbon nucleation, while leaving back all the bio-fuels as by product. Further, slow pyrolysis maintained the uniformity of the final product, as quality control is necessary during the process. Black shining amorphous carbon was collected from the pyrolysis reactor at room temperature, which is then ball milled to make an ultrafine powder. The ultrafine powders thus obtained are then treated at secondary pyrrolysis reactor (with the capacity of 0.06 cm3) at the destination temperature of 900°C with the heating rate of 8°C. However, temperature hold at 600°C was also done during the process and subsequently a little amount of sample was also collected to ensure the formation of graphene nanosheets by the characterization techniques. Several experiments were carried out in order to optimize the temperature for the synthesis process of graphene nanosheets from plastic waste. Finally, black and shining powder of graphene nanosheets were obtained without any further purification or chemical treatment.
Figure 1 shows a flowchart for the process of manufacturing graphene nanosheet from paper waste.
The process 100 of manufacturing graphene nanosheet from paper waste, comprises step 102 stirring a mixture containing distilled water and about 8kg to 12kg of paper waste for about 1 minute to 3 minutes. The process 100 further comprises step 104 filtering the mixture using a filtration net and washing the residue obtained. Then, at step 106 soaking the residue for about 20 minutes to about 40 minutes in a first mixture containing methanol, ethanol and distilled water in a ratio of 2:3:25. Then, at step 108 heating the residue and the first mixture together for about 20 minutes to about 40 minutes at a temperature ranging from 50°C to 70°C and at step 110 obtaining a slurry mixture by removing the residue from the first mixture and rinsing the residue. The process 100 further comprises step 112 performing a first pyrolysis method on the slurry mixture at a temperature ranging from 300°C to 400°C under an inert atmosphere and step 114 obtaining amorphous carbon as product of the first pyrolysis method. Then, at step 116 ball milling the amorphous carbon to obtain an ultrafine powder and step 118 performing a second pyrolysis method on the ultrafine powder at a temperature ranging from 850°C to 950°C. Lastly, at step 120 obtaining graphene nanosheet as product of the second pyrolysis method.
In another embodiment, the graphene nanosheet comprises a dopant selected from a group containing silicon, magnesium, calcium or any combination thereof.
In another embodiment, the paper waste comprises a plurality of strips and wherein each strip of the plurality of strips has a length of less than 11.2 mm and a width of less than 5.75 mm.
In another embodiment, the filtration net has a pore size of about 300µm to about 500µm;
In another embodiment, the first mixture contains about 150 ml to 250 ml of methanol, about 250 ml to 350 ml of ethanol and about 2 to 3 litres of distilled water.
In another embodiment, the reactor chamber used in the first pyrolysis method is made up of stainless steel and having a capacity of 0.41 m3.
In another embodiment, the first pyrolysis method has a heating rate of 5°C per minute.
In another embodiment the inert atmosphere contains N2 gas and wherein N2 gas is introduced at a rate of 20 ml per minute.
In another embodiment, the first pyrolysis method comprises a carbon nucleation process, that generates aromatic carbon nanosheets as product and bio-fuels as by-product.
In another embodiment, the reactor chamber used in the second pyrolysis method has a capacity of the 0.06 m3.

The synthesis of the graphene nanosheets from waste papers was done in two stage pyrolysis process. The final product obtained from the second stage pyrolysis was analyzed by various spectroscopic and imaging techniques and confirmed as few layer graphene nanosheets. The process involves the incorporation of the mixture of lower aliphatic alcohols (C1&C2) to increase the rate of carbon nucleation for the development of graphene nanosheets. When the washed paper sheets soaked in the mixture of methanol and ethanol along with the distilled water and heated at 60°C, the molecules of the methanol and ethanol swell the inner walls of the paper sheets and thereby enhanced the chances of growth of the separated sheets of graphene during the process. Further, during the swelling process of the paper in the solvent mixture, methanol and ethanol creates different kinds of the channelize cavities which helps to enhance the molecular trapping of the charges and channelized charge transportation for the application of energy conversion and storage. Raman spectroscopy is widely used spectroscopic technique to confirm and analyze the quality of graphene nanosheets. The synthesized graphene nanosheets possessed a variety of Raman active modes corresponding to the plane of C-C bond i.e. in plane or out of the plane (Figure 2).
Raman spectrum of thus synthesized graphene nanosheets showed graphitic nature corresponding to the sp2 hybridized carbon atom as shown by the G band at 1582 cm-1 of the Raman spectrum of graphene nanosheets. The G band present in the Raman spectrum of the graphene nanosheets at 1582 cm-1 also showed the Ist order scattering of the sp2 hybridized carbon atoms corresponding to E2g vibrational modes [42-43]. The another well-known peak corresponding to the D band of the graphene nanosheets also observed at 1348 cm-1 due to the presence of sp3 carbon atom in the lattice of sp2 hybridized carbon atoms, which arises surface defects within the graphene nanosheets. Additionally, another 2D band also appears at 2827 cm-1 ,which showed the presence of few layer graphene nanosheets. Further, the intensity of the Raman spectrum of the graphene nanosheets provides useful information such as defects and number of layers in the graphene nanosheets [44-45]. This information’s can be deduced by the calculation of ID/IG and I2D/IG ratios. The low intensity ratios of ID/IG =0.88 and I2D/IG=0.28 showed lesser number of defect concentration with the presence of few layer of graphene nanosheets. However, this D/G ratio depends upon the presence of the oxygenated functional groups present on the upper and lower surface of the graphene nanosheets [46]. The presences of oxygenated functional groups were also found within the synthesized graphene nanosheets as confirmed by using FT-IR spectroscopy. The FT-IR spectra of thus synthesized graphene nanosheets showed different kinds of oxygenated groups at corresponding to their wavenumbers in the FT-IR spectra Figure 3.
A weak and broad peak is obtained at about 534 cm-1 due to out of plane Si-O bending [47], which confirms the presence of silicon within the graphene nanosheets, while some of weak, medium and strong peaks are also observed in FT-IR spectrum of the graphene nanosheets such as weak peak at 710 cm-1 due to =C-H bending vibrations, medium peak at 874 cm-1 due to COC deformation and stretching, strong peak at 1423 cm-1 due to OCH in plane bending vibration, weak peak at 1636 due to C=C stretching vibrations, weak peak at 1799 due to C=O stretching vibrations, weak peak at 2514 due to presence of acidic –OH stretching vibration, weak peak at 2912 due to –C-H stretching vibration and medium peak at 3442 due to –OH stretching vibration.
The XRD spectrum of thus synthesized graphene nanosheets showed three major peaks at 2O= 15.24°, 28.72° and at 40.88°, where the first broad peak at 15.24° showed the characteristic peaks for graphene nanosheets which might be attributed to the presence of the few layer graphene nanosheets due to the presence of various functional groups, while the second peak at 28.72° showed the graphitic nature with the graphene nanosheets with increased interlayer distance due to presence of oxygen containing functional groups, while the another peak at 40.88° showed the characteristic peak for graphene nanosheets (Figure 4).
Further in order to understand the surface morphology of the graphene nanosheets in presence of various functional groups, FESEM images were recorded. The FESEM images of the graphene nanosheets clearly depicted the large area clusters type morphology, while in some places sheets are found with discrete edges, although wrinkles surfaces are also seen at the edge side area. The mean sheets dimension of graphene nanosheets was found to be 30µm×40µm (Figure 5(a-d)).
Additionally, Electron dispersive X-Ray (EDX) spectroscopy was performed in order to analyze the elemental percentage present within the graphene nanosheets (Figure 6). The EDX spectrum showed the presence of carbon (90.38%), oxygen (4.11%), magnesium (1.92%), silicon (2.54%) and calcium (1.05%). The high resolution transmission electron microscopy (TEM) analysis was also performed in order to calculate number of sheets within the stacked of the graphene nanosheets derived from paper waste. TEM images showed that graphene nanosheets exhibits few layer (n<5) stacking of graphene nanosheets with very minute wrinkles and folding which makes good agreement with the XRD analysis. Figure 6 (a-f) demonstrates the sheet structure of the paper waste derived graphene nanosheets in different resolution of the magnification scale. The sheet structure of the graphene nanosheets could be seen from the HRTEM images at low scale magnification (0.5µm) clearly depicted large area sheets of graphene (Figure 6(a)), while almost transparent sheets with interconnected sheets of two or more graphene could be seen at high level magnification (100nm, 50nm and 20nm). The lattice fringes of the graphene nanosheets can be clearly seen in the figure 6 (e) at the magnification of 10nm, which again makes a good agreement with the XRD analysis of the graphene nanosheets. The crystallographic structure of the paper waste derived graphene nanosheets was obtained by SAED method (figure 6 (f)). The SAED graph of the paper waste derived graphene nanosheets showed sharp and clear diffraction pattern as reported in previously published literature [48].
In order to understand the utility of the paper waste derived graphene nanosheets for the application of the energy conversion, UV-visible spectroscopy was performed in order to understand the absorption properties and band gap of the thus synthesized graphene nanosheets. The UV-visible spectrum of thus synthesized graphene nanosheets showed a broad spectrum in the visible region with a peak at 265nm, which gives another evidence for the presence of few layer graphene nanosheets and also makes good agreement with HRTEM analysis (Figure 7).
Further, UV-visible spectroscopy was also used as versatile tool for the calculation of the optical band gap by using Tauc plot for the paper waste derived graphene nanosheets. Therefore, in order to investigate the properties of the paper waste derived graphene nanosheets for energy harvesting applications, optical band gap was evaluated by using Tauc expression, where the absorption coefficient (a) is directly related to the incident photons according to the following relation
(ah?)2 = A(h?-Eg) (1)
where, Eg is known as the optical band gap of the material. So, by using this expression, optical band gap is evaluated from the plot of (ah?) 2 as the function of energy of incident photons. The optical band gap of paper waste derived graphene nanosheets is estimated to be 2.25 eV (Figure 8).
The optical band gap at 2.25 eV showed that it can effectively use for the synthesis of the graphene nanosheets photovoltaic applications. It can be used as effective hole transport materials in the organic solar cell, while the same can be used in DSSCs solar cells as band tuner to make better passage of the charge transportation for the counter electrode. Further, perovskite solar cells with improved device parameters were also reported by the introduction of graphene nanosheets, thus the present graphene nanosheets from paper waste could be used for a variety of photovoltaic applications. Further energy harvesting applications were also investigated in order to get real time application of thus synthesized graphene nanosheets.
Energy Storage Application
The energy storage applications of thus synthesized graphene nanosheets were demonstrated by utilizing them as active layer material for supercapacitors. The charge storage capacity of thus synthesized graphene nanosheets were analyzed in the presence of liquid electrolyte (1 M H3PO4) as well as PVA-H3PO4 gel electrolyte.
Synthesis of gel electrolyte
The polymer electrolyte of PVA-H3PO4 was prepared according to our previous work . In this process, we slowly add the 1 gm of PVA in the hot water (Distilled water) at 90 oC in continuous stirring condition for 1hr. After this, we get the transparent viscous solution of PVA in water. Further, add 1gm of H3PO4 in this viscous solution and stirrer for another 30 min then poured into the petri dish to allow the evaporation of present water at room temperature.
Electrode and device fabrication
In this process, initially we dispersed the 10% of PVDF powder in the acetone and sterrier for 5 hr at room temperature. Then, the desired amount of WP-G was taken and makes a thick paste with above PVDF solution in mortar pastel. After this, the thick paste were coated over the graphite sheets in the area of 1cm x 1cm (~1mg) and kept in the oven for dying overnight. Then, these coated graphite sheets assemble in a two ways as the Table- 1, (i) Cell-1: in this cell structure the milipore filter paper (also act as the separator) placed over the coated graphite sheets and add few drop of electrolyte (1M H3PO4) then the another coated graphite sheets placed over it and make a sandwich like structure. (ii) Cell-2: this cell made with the polymer gel electrolyte (PVA-H3PO4) in which this acts the electrolyte as well as the separator. The PVA-H3PO4 polymer film placed between the two symmetrically coated graphite sheets. Further, these devices investigated for their electrochemical performance.
Table 1. The fabricated cell of WP-G
S.No. Fabricated cells
1. Cell-2: Graphite sheet | WP-G | 1M H3PO4 | WP-G | Graphite sheet
2. Cell-1: Graphite sheet | WP-G | PVA-H3PO4 | WP-G| Graphite sheet

Device Characterization
The electrochemical performance of the fabricated devices investigated under the CHI 600E Instruments, Inc., electrochemical station. During this, we performed the cyclic voltammetry (CV) for the fabricated devices over the potential range of -1 V to 1V at different scan rate from with both the electrolyte systems. After this, the electrochemical impedance spectroscopy(EIS) was performed for the fabricate devices at 10 mHz. Further, galvanostatic charge-discharging (GCD) was performed for the fabricated devices over the potential window of 0 to 1V at different current densities. Then, the specific capacitances were calculated for the fabricated devices with the help of above performed electrochemical measurements.
Result and discussion
Cyclic Voltammetry
The cyclic voltammerty of both devices (Figure 9) show the very good reversibility over the performed voltage range at the scan rate of 10 mV/s, 20 mV/s, 50 mV/s, 100 mV/s and 200 mV/s. The CV curve of Figure 9 (a) shows the nearly rectangular shape due to lower contact resistance and electrical double layer capacitance. On the other hand, some places in the CV curve show the several peaks which indicate the few portion of the capacitance contributed by the faradic redox reaction i.e, the capacitance arise due to the pseudo capacitance. These both kind of characteristic present in the WP-G which enhance the overall specific capacitance of the device. On the other hand, Figure 9 (b) shows the more rectangular shape than the Figure 9 (a). Also, this device not show any sharp peaks in the CV curves which indicated the capacitance arises via purely electrical double layer capacitance. The specific capacitance via CV shows in Table 2 for both devices which estimated by the following formula-
C= i/s
Where i is the current, s is the rate of scan.
From this curve and using above equation show the highest specific capacitance of 45.6 F/g for the cell-1 and 3.168 F/g for the cell-2 at the scan rate of 10 mV/s.
Table: 2 Specific capacitance obtained from the cyclic voltammetry analysis
Cells Specific Capacitance (F/g) at 10mV/s Specific Capacitance (F/g) at 20 mV/s Specific Capacitance (F/g) at 50 mV/s Specific Capacitance (F/g) at 100 mV/s Specific Capacitance (F/g) at 200 mV/s
Cell-1 45.6 28.5 19.44 15.5 12.5
Cell-2 3.168 3.565 3.456 1.2 2.92

Electrochemical Impedance spectroscopy (EIS)
EIS of the fabricated devices (Figure 10) shown by Nyquist plot were performed for the investigation of the resistance and specific capacitance at 10 mHz. In these graph, both devices shows the steeply rising incident toward the lower frequency region which indicate the capacitance behavior shown by the WP-G with the electrolyte. On the other hand, the small semicircle shown by the both devices (more prominent for the Figure 10 (b)) in the higher frequency region which is arises due to the bulk properties of both electrolyte for the respective devices and charge transfer process. Further, including all the parameter, calculated the specific capacitance (Table 3) for the both devices via following equation-
C = 1/(2pf Z'')
Where f is the frequency of applied AC signal and Z'' is the imaginary part of the impedance Z at 10 mHz. Here, the specific capacitance via this technique is 27.9 for cell-1 and 3.09 for Cell-2.
Galvanostatic charge-discharge
Figure 11 show the charging discharging behavior of the both cells at 1A/g and 2A/g of current densities over the potential window of 0 to 1 V. Both devices show the nearly triangular shape of curve over performed current densities which arise due to capacitive behavior of the both cells. Further, these curves used for the estimation of specific capacitance behavior of the both cell by using following equation-
C = (i?t)/(m?V)
Where i is the scan rate, m represent the mass loading over the electrode and ?V/?t is the linear part slop in the discharge curve. Further, evaluate the specific capacitance shown in Table 3 for both cells by using above equation. The highest specific capacitance value shown by the cell-1 and cell-2 is 9.0 F/g and 1.39 F/g, respectively, at the 1A/g of current density. Figure 11 shows GCD analysis of WP-G (a) Cell-1- With 1M H3PO4 electrolyte and (b) Cell- 2-With PVA-H3PO4 polymer gel electrolyte.
Table 3. The specific capacitance value of EIS and GCD for the WP-G with 1M H3PO4 and PVA-H3PO4.
Cells Specific Capacitance using EIS (F/g) Specific Capacitance using Galvanostatic charge/discharge (F/g) at 1A/g Specific Capacitance using Galvanostatic charge/discharge (F/g) at 2A/g
Cell-1 27.9 9.0 3.0
Cell-2 3.09 1.39 0.42
The specific capacitance values evaluate by using above techniques for both cells. In these, cells we observed the cell-1 shows the highest capacitance then the cell-2. This higher capacitance behavior of cell-1 for all uses techniques because the aqueous electrolyte (i.e., 1M H3PO4) always shows higher mobility of electrolyte ions. On the other hand, cell-2 shows lower specific capacitance due the immobilization of electrolyte ions in the PVA matrix. Thus, these electrolyte ions are less accessible results in the lower specific capacitance.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of the invention.

We Claim:

1. A process of manufacturing graphene nanosheet from paper waste, comprising:
i. stirring a mixture containing distilled water and about 8kg to 12kg of paper waste for about 1 minute to 3 minutes;
ii. filtering the mixture using a filtration net and washing the residue obtained;
iii. soaking the residue for about 20 minutes to about 40 minutes in a first mixture containing methanol, ethanol and distilled water in a ratio of 2:3:25;
iv. heating the residue and the first mixture together for about 20 minutes to about 40 minutes at a temperature ranging from 50°C to 70°C;
v. obtaining a slurry mixture by removing the residue from the first mixture and rinsing the residue;
vi. performing a first pyrolysis method on the slurry mixture at a temperature ranging from 300°C to 400°C under an inert atmosphere;
vii. obtaining amorphous carbon as product of the first pyrolysis method;
viii. ball milling the amorphous carbon to obtain an ultrafine powder;
ix. performing a second pyrolysis method on the ultrafine powder at a temperature ranging from 850°C to 950°C; and
x. obtaining graphene nanosheet as product of the second pyrolysis method.

2. The process as claimed in claim 1, wherein the graphene nanosheet comprises a dopant selected from a group containing silicon, magnesium, calcium or any combination thereof.

3. The process as claimed in claim 1, wherein the paper waste comprises a plurality of strips and wherein each strip of the plurality of strips has a length of less than 11.2 mm and a width of less than 5.75 mm.

4. The process as claimed in claim 1, wherein the filtration net has a pore size of about 300µm to about 500µm;

5. The process as claimed in claim 1, wherein the first mixture contains about 150 ml to 250 ml of methanol, about 250 ml to 350 ml of ethanol and about 2 to 3 litres of distilled water
6. The process as claimed in claim 1, wherein the reactor chamber used in the first pyrolysis method is made up of stainless steel and having a capacity of 0.41 m3.

7. The process as claimed in claim 1, wherein the first pyrolysis method has a heating rate of 5°C per minute.

8. The process as claimed in claim 1, wherein the inert atmosphere contains N2 gas and wherein N2 gas is introduced at a rate of 20 ml per minute.

9. The process as claimed in claim 1, wherein the first pyrolysis method comprises a carbon nucleation process, that generates aromatic carbon nanosheets as product and bio-fuels as by-product.

10. The process as claimed in claim 1, wherein the reactor chamber used in the second pyrolysis method has a capacity of the 0.06 m3.