Graphene Oxide Thin Films: Synthesis and Optical Characterization

ChemistrySelect Communications doi.org/10.1002/slct.202002481 z Materials Science inc. Nanomaterials & Polymers Graphene Oxide Thin Films: Synthesis and Optical Characterization J. J. Prías Barragán,[a] K. Gross,[b] José Darío Perea,[c] Niall Killilea,[d] Wolfgang Heiss,[e] Christoph J. Brabec,[f] H. Ariza Calderón,[g] and Pedro Prieto[h] The oxidized derivative of graphene named Graphene oxide (GO) are attractive materials as optoelectronic devices due to their optical response in the mid-infrared wavelength spectral range; however, very large-scaled synthesis methods and optical characterization are required. Here, GO thin films are fabricated on quartz by implementing simple two-step pyrolysis processes by using renewable bamboo as source material. The effect of carbonization temperature (TCA) on the compositional, vibrational, and optoelectronic properties of the system are investigated. It was found that as TCA increases, graphite conversion rises, oxygen coverage reduces from 17 % to 4 %, and the band-gap energy monotonically decreases from 0.30 [a] Dr. J. J. Prías Barragán Interdisciplinary Institute of Sciences, Universidad del Quindío, Carrera 15 Calle 12 Norte, 630001 Armenia, Colombia. Electronic Instrumentation Technology Program, Universidad del Quindío, P. O. Box 661, Armenia, Colombia and Center of Excellence on Novel Materials (CENM) and Department of Physics, Universidad del Valle, P. O. Box 25157, Cali, < Colombia [b] Dr. K. Gross Center of Excellence on Novel Materials and Department of Physics, Universidad del Valle, P. O. Box 25157, Cali, Colombia [c] Dr. J. Darío Perea Department of Chemistry and Department of Computer Science, University of Toronto, Toronto, ON M5S 3H6, Canada and Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander-Universität Erlangen-Nürnberg, Martensstrasse 7, 91058 Erlangen, Germany [d] Dr. N. Killilea Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander-Universität Erlangen-Nürnberg, Energy Campus Nürnberg, Fürther Straße 250, 90429 Nürnberg, Germany [e] Prof. Dr. Wolfgang Heiss Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander-Universität Erlangen-Nürnberg, Energy Campus Nürnberg, Fürther Straße 250, 90429 Nürnberg, Germany [f] Prof. Dr. C. J. Brabec Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander-Universität Erlangen-Nürnberg, Martensstrasse 7, 91058 Erlangen, Germany and Forschungszentrum Jülich GmbH Helmholtz-Institut Erlangen-Nürnberg for Renewable Energy (IEK-11) Immerwahrstraße 2, 91058 Erlangen, Germany [g] Dr. H. A. Calderón Interdisciplinary Institute of Sciences, Universidad del Quindío, Carrera 15 Calle 12 Norte, 630001 Armenia, Colombia [h] Prof. Dr. Pedro Prieto Center of Excellence on Novel Materials (CENM) and Department of Physics, Universidad del Valle, P. O. Box 25157, Cali, Colombia ChemistrySelect 2020, 5, 11737 – 11744 to 0.11 eV. Theoretical predictions of the energy band-gap variations with the oxide coverage obtained via density functional theory (DFT) computational simulations agree well with the experimental results, providing evidence of oxygen-mediated charge-transport scattering. Interestingly, in the optical response, increased TCA results in a blue-shift of the absorption and the absorbance spectrum can be correlated with the large size distribution of the graphitic nano-crystals of the samples. These results suggest that graphene oxide-bamboo pyroligneous acid (GO) thin films exhibit optoelectronic response useful in developing photodetectors and emitter devices in the mid-infrared (MIR) spectral range. 1. Introduction Given its unique charge transport and optical properties, graphene is a promising material for integration into microelectronics and nano-electronics.[1–2] It is known that graphene has a large specific surface area (2630 m2 g 1), good electrical conductivity (1.04 × 102 Sm 1), good thermal conductivity (∼ 5000 Wm 1K 1), high intrinsic mobility (250.000 cm2v 1s 1) optical transmittance (∼ 97.7 %), and high Young’s modulus (∼ 1.0 TPa).[3–9] Thus, graphene and graphene-related materials can be used in numerous technological applications, including optoelectronics, sensor technology, energy storage, spintronic, transparent electrodes, among many others.[10–13] In this regard, several synthesis techniques have been proposed in literature; however, most of these techniques are still costly or need time-consuming multi-step chemical and physical processes or use ultra-high vacuum or employ noneco-friendly chemical oxidation/reduction reactions, making them less attractive for large-scale manufacturing. Currently, reduction from Graphene oxide (GO) is one of the cheapest and fastest methods of graphene production. Reduced GO (rGO) can be described as an reduced oxidized form of graphene, decorated mostly by hydroxyl, carboxyl and epoxy functional groups distributed randomly along the hexagonal sp2 network of carbon atoms.[14–17] The oxygen functional groups of GO create sp3 C O sites; therefore, GO can be visualized as a two-dimensional network of sp2 and sp3 bonded atoms, in contrast to an ideal graphene sheet consisting of 100 % sp2 carbon atoms. Graphene oxide is often described as an electrical insulator due to the presence of sp3 C O bonding; nevertheless, by reducing the C O level, the sp2 hybridization 11737 © 2020 Wiley-VCH GmbH ChemistrySelect Communications doi.org/10.1002/slct.202002481 is restored and electrical conductivity is enhanced. Specifically, by reducing the oxygen content, GO undergoes insulatorsemiconductor-semimetal transitions. One of the most notable differences between GO and graphene is the optoelectronic response arising from the presence of finite band-gap due to the oxygen coverage.[18] Thus, the photoluminescence can be tuned from blue to red to infra-red (IR) emission.[19] The multi-functionality given by oxides, in combination with the exceptional properties of graphene, permit considering GO as a versatile candidate material for next-generation electronics and optoelectronics, as well as in energy conversion, storage technologies, and solar cells.[9–13,20–22] Particularly, one of the possible applications of rGO is as electrodes for photovoltaic devices, as replacement of indium thin oxide (ITO)[21,22] and selective contact in solar cells.[11,24] Graphene oxide and graphene-based materials exhibit attractive significant interest in the field of solar cells due to the excellent GO dispersion in common solvents; furthermore, inexpensive and solution-based processes and excellent stability are other advantages.[25–36] Integration of rGO into technologically viable devices sometimes requires obtaining rGO in the form of thin films; however, most synthesis techniques yield only micron-sized GO flakes. Thus, to produce films of layered GO flakes, the GO flakes are dispersed in adequate solvents and, subsequently, deposited on substrates by implementing some deposition techniques, like dip coating, spin coating, spray coating, and Langmuir-Blodgett method.[28–31] With dip coating and spin coating, it is usually difficult to guarantee uniformity and continuity of the deposition due to aggregation of GO. In view of this, we propose a new, simple, cost-effective pyrolytic method to synthetize graphene oxide multilayers as thin films, which can be deposited over rigid or flexible substrates, by using bamboo pyroligneous acid (BPA) as source material with advantages, such as low time consumption (30 h) and environmental sustainability.[32,33] This work introduces experimental and theoretical approaches to determine the band-gap energies in GO thin films in the range of low oxygen coverage regime, < 17 %. Additionally, to determine the optoelectronic response of GO films/quartz, experimental characterization was conducted via XRD, FTIR, RAMAN, UV-VIS, PL-Vis-NIR and PLMIR measurements; additionally, the conductor-like screening model for real solvents (COSMO-RS) was employed to visualize the surface charge density considering different oxygen coverage.[37–40] Here, we observed that by increasing the oxygen content, the electron acceptor and donor abilities increase in the material, showing electron-hole pair density distributions by multifunctional oxide presence. This work presents a new synthesis method and optical properties of GO /quartz thin films and discusses possible future opportunities and challenges of these materials in the manufacture of organic photovoltaic solar cells. 2. Results and Discussions 2.1. Synthesis, structural, and optical properties of GO thin films Starting with the Bamboo as a precursor material, the GO thin films were synthetized by using a double-thermal decomposition (DTD) method in a pyrolysis system by controlling TCA and nitrogen atmosphere, as shown schematically in Figure 1(a). Specifically, the first thermal decomposition process introduces Bamboo (Guadua angustifolia Kunth, macana biotype) into the pyrolysis chamber to collect the BPA at a carbonization temperature of 973 K. The BPA is collected in the form of a viscous liquid, which is thereafter deposited onto quartz substrates by using roll-coating method. The BPA on quartz substrate undergoes a second thermal decomposition process, where the TCA can be varied from 573 to 973 K. For this study, GO thin films on quartz were fabricated at different carbonization temperatures (TCA = 573, 673, 773, 873, and 973 K). The pictures of our samples for the flexible and rigid GO thin films synthesized by using the DTD method are displayed in Figure 1(b). For verified the structural properties as well as the functional oxygen groups dependent on TCA measures of XRD and FTIR spectroscopy were performed. The XRD patterns of GO/quartz, as presented in Figure 2(a), show a broad (002)-peak around 2Θ = 21°, typical of rGO, which shifts to larger values with increasing TCA, indicating lower inter-planar d spacing for higher TCA. Likewise, as TCA increases, the Bragg reflection at (101) becomes visible, indicating improved structural order for higher TCA. The FTIR spectra displayed in Figure 2(b) shows that at the lowest TCA, several peaks localized at 3426, 2927–2850, 1680, 1590, 1435–1370, 1157, and 1066 cm 1 attributed to Figure 1. (a) Schematics of the two-step process used for synthesis of GO /quartz thin films. (b) Digital images of the GO thin films on flexible and rigid substrates. ChemistrySelect 2020, 5, 11737 – 11744 11738 © 2020 Wiley-VCH GmbH ChemistrySelect Communications doi.org/10.1002/slct.202002481 Figure 2. (a) XRD pattern in GO samples. (b) FTIR and c) Raman spectra of GO samples for different carbonization temperatures, respectively. O H, C H, CO2, C=O, C=C, C H, C O C, and C O bonds, respectively, are present; however, when TCA increases, the organic compounds and oxides gradually evaporate, obtaining mainly the presence of the C–H, C=C, and C O bonds for the highest TCA value. These results agree with the peak values reported by Yan Geng et al.,[34] and Xinlong Wang and coChemistrySelect 2020, 5, 11737 – 11744 workers.[35] These initial results give indications that higher TCA promotes optimization of the graphitic structure of the thin films. Also, the FTIR spectra in GO sample synthesized at TCA = 673 K presents more multifunctional oxides that GO sample obtained at 973 K, indicating that increases the functional groups presence in the samples and increase the band-gap energy as presented in electrical characterization section. Due to the organic compounds and multifunctional oxides presences in the GO samples, the multiplicity of vibrational modes in FTIR spectra’s is great and this probably induced the effect of screening over the electronic energy states and for this reason from the experimental view, FTIR spectra’s in GO samples only offers information about the vibrational behavior related to the functional groups without contributions of the electronic energy states as the band-gap energy. Therefore, the electrical characterization gives directly the information about the electronic energy states in GO samples as presented and discussed in section 2.1. Then, the presences of multifunctional oxides opening of the band-gap energy by increment in the multifunctional oxides presence as expected for a semiconductor material, it might be more relevant for future applications in electronics. Figure 2(c) presents the Raman spectrum of GO sample fabricated at 973 K; according to this spectrum, the characteristic G-band peak around 1560 cm 1 and D-band peak around 1350 cm 1 can be observed. The former indicates the formation of a graphitized structure, while the latter corresponds to the disorder-induced phonon mode. A third peak was identified around 1590 cm 1, associated with the presence of boundary defects. The wide 2D and D + G bands around the 2800 cm 1 value suggest the presence of many GO multilayers with edges, defects, and sp3 regions.[2] Now looking at the measurements of the optical properties. Absorption measurements in the UV-visible range spectra of GO/quartz at room temperature are visualized in Figure 3(a). The measurements evidence a broadband light absorption from 200 nm to 1100 nm for all TCA. Interestingly, increasing TCA results in a blue-shift of the absorption. The blue-shift in absorbance spectrum can be correlated with the large size distribution of the graphitic nano-crystals of the samples, as confirmed via Raman and HR-TEM measurements.[2,3] The GO samples exhibit optical absorption extended all over the visible regime, this behavior can be attributed to the presence of different oxide coverage as presented in Table 1 and a structural configuration of the Graphene oxide multilayers or graphite oxide, as presented in Figure 3(a), here UV-Vis spectra in Graphite also demonstrate this optical characteristic like a spectral reference. In Table 1 we can observe that as the carbonization temperature increases, the oxide coverage decreases. These small differences in this behavior were not explored in this work, because more information about the complementary characterization would be needed. These results will be discussed in future work. However, they were consistent in both experimental measurements of composition using XPS and EDX techniques, as shown in Table 1. The observed presence of oxygen functional groups causes formation of sp3-islands in GO multilayer, which produces disruption of the π-network and, thus, opens up a band-gap in 11739 © 2020 Wiley-VCH GmbH Communications doi.org/10.1002/slct.202002481 ChemistrySelect Figure 3. (a) Absorption spectra of GO /quartz thin film at different TCA. (b) MIR-PL spectra analysis in GO at TCA of 673 K. (c) MIR-PL spectra in GO-BPA for different TCA. (d) MIR-PL spectral analysis of the band-to-band transition region in GO at TCA of 673 K. The red curve corresponds to the fit by using Equation (1). Table 1. Comparison between elemental composition measurements by XPS and EDS techniques in GO samples obtained at different TCA. GO TCA (K) XPS measurements C-1 s O-1 s (%) (%) N-1 s (%) Na-1 s (%) EDS measurements C K O K (%) (%) N K (%) Na K (%) Difference ΔO/O (%) 673 773 873 973 85.71 92.15 87.49 94.00 0.70 0.69 0.61 0.75 0.60 – 2.21 – 85.30 90.74 89.95 91.07 – – – – 1.52 1.42 – 2.77 1.46 9.50 3.71 17.33 12.99 7.16 9.69 5.25 the electronic structure, mainly by epoxy groups present as C O C. Figure 3(b) shows the MIR- photoluminescence (PL) spectra of GO /quartz obtained at TCA = 673 K and its respective fitting lines by using deconvolution of eight Gaussian functions as contributions associated to exciton-phonon coupling, exciton emissions, and band-to-band transition. Also, in Figure 3(b) it is indicated as blue arrow the CO2 absorption, which does not provide any luminescence; however, it provides absorption within the optical path which is used to measure the emission spectra. Additionally, in Figure 3(c) the same analysis for the MIR-PL spectra in GO films/quartz measured at the different TCA is presented. As observed before, three characteristic regions are distinguished: region-(i) at lower energies, in a range of 0.20–0.30 eV, different exciton-phonon (LO, longitudinal optical phonon) emissions (EXA + 1LO, EXD + 1LO, EXn1 + 1LO, and EXn2 + 1LO) were identified; from here, a ChemistrySelect 2020, 5, 11737 – 11744 13.18 7.84 10.05 6.16 excitonic bound energy of 66 meV was obtained, expected for a narrow gap semiconductor.[3] Region-(ii) at an energy range of 0.30–0.34 eV, where excitonic radiative transitions (as acceptor (EXA), donor (EXD), EXn1 and EXn2,) could be identified. Region(iii) at an energy range of 0.34–0.37 eV, where band-to-band radiative transitions are observed. To obtain the band-gap value belonging to the third region, as shown in Figure 3d, we used the expression for band-to-band transition presented in equation (1):[31] Ið�hwÞ ¼ I0 �hw Eg �1 2 exp � �hw Eg kT � where E = h � w is the energy measured by the MIR-PL system used (eV as unit), Eg is the band-gap energy value of the material studied (eV as unit), k is the Boltzmann constant, T is 11740 © 2020 Wiley-VCH GmbH ChemistrySelect Communications doi.org/10.1002/slct.202002481 the absolute temperature, at room temperature the thermal energy is given by kT that is 25 meV, and I0 is an experimental constant attributed to the transfer function of the MIR-PL system. Considering the latter values, a band-gap energy value of 0.34 eV was determined for this sample; this value agrees with previous values of band-gap energy reported by our group.[33] These results of the fundamental energy values of the band-gap coincide with the range of values of 0.11–0.40 eV, as reported by Daeha Joung and Saiful I. Khondaker.[53] Our results correspond to the narrow band-gap semiconductor, as expected.[33,53] Also, as it is presented in Figure 3a, the energy values that vary from 2.5 to 5.0 eV, which correspond to energy transitions in other critical points (i. e. E1 or E1 + ΔE1); however, it is necessary to perform more experiments with other optical characterization techniques, to confirm the nature of these results. In general, GO MIR-PL spectra show slight modifications by varying the TCA; however, these present a good exciton-phonon coupling transitions that could enhance the optical response and quantum efficiency of this material in applications as selective contact or barrier contacts in organic solar cells. Additionally, PL-Vis-NIR measurements were performed; in this regime, the light emission intensity was very low and signals measured were quite noisy (not shown in this work). The latter is a very convenient response for applications as selective contact in organic solar cells. 2.2. Electrical characteristics of single GO nanoplatelets For the electrical characteristics of single GO, the Transmission Electron Microscopy (TEM), presented in Figure 4(a)–(b) was employed. Its measurements revealed high electron transparency and low corrugation effects present in the samples, like graphene oxide multilayers or nanoplatelets. The low corrugation effect observed by TEM in graphene oxide multilayers obtained from BPA offers a technological advantage compared with the traditional GO sheets, given that it is easier to deposit electrical contacts on a flat surface than on a highly corrugated surface.[14,15] Figure 4(c)–(d) presents high-resolution-TEM (HR-TEM) images of GO multilayers at 5 nm scale for 4 % and 17 % oxygen coverage, both insets show electron diffraction pattern of GO samples. It is possible to observe diffuse rings revealing that GO exhibit polycrystalline structure behavior. Figure 4(e)–(f) shows a HR-TEM zoom and the proposed molecular structure obtained via turbo-mole modeling software, respectively. Figure 4(g) presents the GO molecular structural model proposed in this work; here, the blue balls represent carbon atoms, red balls represent oxygen atoms, and white balls represent hydrogen atoms. It is worth noting the good agreement of the simulated structure with the observed structure obtained through HR-TEM imaging. To gain more insight in the energy associated with the optoelectronic response, we obtained the band-gap energy as a function of oxygen content. Figure 5(a) shows the experimental (green circles) and the DFT-B3LYP/6-31G level of theoretical simulation (blue circles) band-gap dependence with oxygen percentage. The room-temperature electrical characterization ChemistrySelect 2020, 5, 11737 – 11744 Figure 4. TEM images in GO multilayers obtained from BPA. a) and b) Flat surfaces with 5 % and 17 % oxide coverage, respectively. White arrows represent the nanoplatelets border. c) and d) HR-TEM image in samples with 5 % and 17 % oxide coverage; respectively, both insets show a characteristic GO electron diffraction patterns and show diffuse rings that can be attributed to disorder by the oxides present. e) and f) Presents an HR-TEM image zoom in the flat surface of the samples with superposition of the GO model proposed. g) The GO molecular model proposed in this work is like a GO Lerf-Klinowski model and considers carboxyl, hydroxyl, and epoxy functional groups identified by using FTIR and reported previously by our group.[41–43] presented in Figure 5(a) was carried out by using the four-point method, as described in the experimental description section and previously reported by our group.[33] It was found that decreasing oxygen coverage increases electrical conductivity in GO multilayers, as expected; this behavior can be attributed to carrier-impurity interactions. To obtain the band-gap energy, we consider the relation for the electrical conductivity:[33] s ¼ s0 exp ð-Eg =2kB TÞÞ (2) here, σ0 = 2x104 S m 1 is considered the electrical conductivity reported for graphite at room temperature and kBT as 25 meV at room temperature. Eg, the band-gap energy, was determined for each oxygen coverage obtained via EDX in our GO 11741 © 2020 Wiley-VCH GmbH ChemistrySelect Communications doi.org/10.1002/slct.202002481 Figure 5. a) Comparison between experimental data and theoretical calculus of the oxygen coverage dependence on the band-gap energy in GO samples. Theoretical results were performed under DFT-6-31G/B3LYP quantum theory level. b) Visualization of surface charge screening density, as predicted by the conductor-like screening model for real solvents (COSMO-RS) for the GOs under study. c) The GO σ profile. multilayers, as shown in Figure 5(a). Band-gap energy values (green circles) show a variation from 0.30 to 0.11 eV by decreasing oxygen content, as expected for a narrow-gap semiconductor behavior and it was determined by using equation (2). The red fit curve is the general quadratic dependence of the bandgap with the scatter center X applied for semiconductors.[41,42] The theoretical predictions of the energy band-gap variations with the oxide coverage obtained via DFT computational simulations agree with the experimental results, providing evidence of oxygen-mediated charge-transport scattering. In Addition, the conductor like screening model for real solvent (COSMO-RS) implicit solvation model was employed to visualize the surface charge screening density throughout the molecule.[37–40] Figure 5(b) shows surface charge screening density for a representation of 12 % oxygen at GO. Figure 5(c) presents the quantity of the electrical surface charge screening density (better known as the σ profile) of GO structures for ChemistrySelect 2020, 5, 11737 – 11744 different oxygen coverages varying from 4 % to 17 % throughout the molecule. The surface charge density, as calculated by the COSMO-RS model, is represented by green, blue, and red zones, representing neutral, negative, and positive charge density values, respectively, or, in other words, the specific polarity on the molecular surface. As such, the negative surface charge density of the molecule is located on the right side of the σ profile graph and has positive σ-values, while the positively charged parts are located on the left side and feature negative σ-values (Figure 5(c)). It was observed that increasing oxide coverage increases the number of electron-hole pairs in the GO molecules, as expected. In general, the central region of the σ profile is associated with nonpolar or weakly polar parts of the molecule, while strongly polar and potentially hydrogen bonding acceptor regions appear on the right-hand side and donor regions on the left-hand side of the σ profiles. The carbon zones consist predominantly of nonpolar regions (green in the surface charge screening density visualizations in 11742 © 2020 Wiley-VCH GmbH ChemistrySelect Communications doi.org/10.1002/slct.202002481 Figure 5(b), which can be linked to exposed surfaces of carbon atoms. The peaks located in the hydrogen bonding acceptor zones correspond to oxygen atoms (red areas in the surface charge density), for the GOs this red region is due to the epoxy groups in Figure 5(b). Conversely, the peaks located in the hydrogen bonding donator region of the σ profile correspond to hydrogen atoms of the alkyl side chain and hydroxyl groups (light blue regions). Furthermore, it was found that increasing oxygen coverage increases electron-hole pairs and electron acceptor-donor abilities. Therefore, DFT simulations show that in GO sheets the electron donor abilities are more abundant than electron acceptor abilities, like p-type narrow gap semiconductor behavior and these results suggests that the main contribution of the band-gap energy can be attributed to epoxy group presence in GO films. Understanding the effect of epoxy groups in electrical and optical properties of molecular GO is of great interest in the basic interpretation of rGO behavior in many applications, like energy storage, catalyst binder, batteries, and micro-lattices among others.[44–52] Also, some challenges of GO thin films in organic photovoltaic solar cells may be, the evaluation of film versatility as interface material for electronics, the device compatibility of solvents and the influence of film homogeneity in the electronic devices. Supporting Information Summary Experimental section including synthesis, sample preparation, and characterization techniques, in addition to the computational methodology are given in the supporting information. Acknowledgments This work was funded in part by Interdisciplinary Institute of Sciences of Universidad del Quindío and the Center of Excellence on Novel Materials at Universidad del Valle under project IC10024. A part of this work was performed at the “Energy Campus Nürnberg” where it was supported by the “Aufbruch Bayern” initiative of the State of Bavaria. Prof. Dr. Christoph J. Brabec (CJB) acknowledge funding by the Deutsche Forschungsgemeinschaft (DFG)- Projektnummer 182849149- SFB 953. As well as, CJB and Prof. Dr. Wolfgang Heiss and Dr. Niall Killilea acknowledge funding through the state of Bavaria for the Energy Campus Nurnberg (EnCN II). Jose Dario Perea acknowledge the University of Toronto and the Ministerio de Ciencias y Tecnologia Colombia-Colciencias. Conflict of Interest The authors declare no conflict of interest. 3. Conclusions In summary, we have reported the first experimental investigation of UV-VIS, FTIR, MIR-photoluminescence (PL), XRD, and Raman in GO films/quartz. These results have shed light on the mechanism involved in light-absorption processes of GO films on quartz substrates and the optical and conductive effects of the hole-electron pairs presents in the samples given mainly by the presence of C O C multifunctional oxide, suggest that GO samples material can be a possible future candidate material in organic photovoltaic solar cells. The experimental and theoretical approach to determine opening band-gap energies in GO multilayers, obtained from bamboo tar as precursor, for low oxide coverage regimen, less than 17 %, were studied and found mainly that C O C bonds can influence this behavior. Graphene oxide multilayered samples exhibit morphological, structural, vibrational, and electrical properties, similar to the same properties exhibited by the rGO obtained through more sophisticated techniques. Experimental and theoretical results of electrical properties suggest that GO multilayers exhibit ptype narrow gap semiconductor behavior. A COSMO-RS molecular model based on ab initio density functional theory quantum chemistry calculations was proposed and agrees with the fine experimental measurements of electrical characterization. Hence, our model provides essential ideas of design criteria and enable identifying suitable processing guidelines for existing and new high-performance blends from the outset. Keywords: graphene oxide · band-gap energy · oxygen coverage · HR-TEM images · Photoluminescence · UV-Vis · DFT computational simulations · COSMO-RS [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] ChemistrySelect 2020, 5, 11737 – 11744 11743 F. Li, X. Jiang, J. Zhao, S. Zhan, Nano Energy 2015, 16, 488–515. X. Wan, G. Long, L. Huang, Y. Chen, Adv. Mater. 2011, 23, 5342–5358. S. Park, R. S. Ruoff, Nat. Nanotechnol. 2009, 4, 217. A. K. Geim, K. S. Novoselov, Nat. Mater. 2007, 6, 183. K. I. Bolotin, K. J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, H. L. Stormer, Solid State Commun. 2008, 146, 351. S. V. Morozov, K. S. Novoselov, M. I. Katsnelson, F. Schedin, D. C. Elias, J. A. Jaszczak, A. K. Geim, Phys. Rev. Lett. 2008, 100, 016602. C. Lee, X. D. Wei, J. W. Kysar, J. Hone, Sci. Rep. 2008, 321, 385. V. Singh, D. Joung, L. Zhai, S. Das, S. I. Khondaker, S. Seal, Prog. Mater. Sci. 2011, 56, 1178. A. A. Balandin, S. Ghosh, W. Z. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C. N. Lau, Nano Lett. 2008, 8, 902. M. Diba, D. W. H. Fam, A. R. Boccaccini, M. S. P. Shaffer, Prog. Mater. Sci. 2016, 82, 83–117. W. Cai, Y. Zhu, X. Li, R. D. Piner, R. S. Ruoff, Appl. Phys. Lett. 2009, 95, 123115. Y. Zhu, S. Murali, W. Cai, X. Li, J. W. Suk, J. R. Potts, R. S. Ruoff, Adv. Mater. 2010, 22, 3906. H. Kim, B. Yang, M. M. Stylianakis, E. Kymakis, S. M. Zakeeruddin, M. Grätzel, A. Hagfeld, Cell Rep. Phys. Sci. 2020, 100053, 1. S. Kim, D. D. Kulkarni, M. Henry, P. Zackowski, S. S. Jang, V. V. Tsukruk, A. G. Fedorov, Appl. Phys. Lett. 2015, 106, 133109. F. Bonaccorso, Z. Sun, T. Hasan, A. C. Ferrari, Nat. Photonics 2010, 4, 611. Y. You, V. Sahajwalla, M. Yoshimura, R. K. Joshi, Nanoscale 2016, 8, 117. A. Ambrosi, C. K. Chua, N. M. Latiff, A. H. Loo, C. H. A. Wong, A. Y. S. Eng, A. Bonanni, M. Pumera, Chem. Soc. Rev. 2016, 45, 2458. M. R. Rezapour, C. W. Myung, J. Yun, A. Ghassami, N. Li, S. U. Yu, A. Hajibabaei, Y. Park, K. S. Kim, ACS Appl. Mater. Interfaces 2017, 9, 24393– 24406. K. P. Loh, Q. Bao, G. Eda, M. Chhowalla, Nat. Chem. 2010, 2, 1015. H. Choi, S. Jung, J. MinSeo, D. Chang, L. Daic, J. Baek, Nano Energy 2012, 1, 534. © 2020 Wiley-VCH GmbH ChemistrySelect Communications doi.org/10.1002/slct.202002481 [21] J. Liu, Y. Xue, M. Zhang, L. Dai, Mater. Res. Soc. Bull. 2012, 37, 1265. [22] J. G. Radich, P. J. McGinn, P. V. Kamat, Electrochem. Soc. Interface 2011, 20, 63. [23] C. Chung, S. Narra, E. Jokar, H. Wu, E. W. Diau, J. Mater. Chem. A. 2017, 5, 13957. [24] J. S. Yeo, J. M. Yun, Y. S. Jung, D. Y. Kim, Y. J. Noh, S. S. Kim, S. I. Na, J. Mater. Chem. A. 2014, 2, 292. [25] J. S. Yeo, R. Kang, S. Lee, Y. J. Jeon, N. Myoung, C. L. Lee, D. Y. Kim, J. M. Yun, Y. H. Seo, S. S. Kim, S. I. Na, Nano Energy 2015, 12, 96. [26] Z. Wu, S. Bai, J. Xiang, Z. Yuan, Y. Yang, W. Cui, X. Gao, Z. Liu, Y. Jin, B. Sun, Nanoscale 2014, 6, 10505. [27] J. K. Kim, S. J. Kim, M. J. Park, S. Bae, S. P. Cho, Q. G. Du, D. H. Wang, J. H. Park, B. H. Hong, Sci. Rep. 2015, 5, 14276. [28] H. B. Sun, J. Yang, Y. Z. Zhou, N. Zhao, D. Li, Adv. Perform. Mater. 2014, 29, 14. [29] H. Anderson, R. Tito, A. Habermehl, C. Müller, S. Beck, C. R. Nieto, G. Hernández Sosa, M. E. Quintana-Caceda, Appl. Opt. 2017, 56, 7774. [30] S. H. Fei, W. Can, S. Z. Pei, Z. Y. Liang, J. K. Juan, Y. G. Zhen, Sci ChinaPhys Mech. Astron. 2015, 58, 014202. [31] X. Luo, K. Ma, T. Jiao, R. Xing, L. Zhang, J. Zhou, B. Li, Nanoscale Res. Lett. 2017, 12, 1. [32] J. J. Prías-Barragán, K. Gross, H. Ariza-Calderón, P. Prieto, Phys. Status Solidi A. 2016, 213, 85. [33] K. Gross, J. J. Prías-Barragán, S. Sangiao, J. M. De Teresa, L. Lajaunie, R. Arenal, H. Ariza-Calderón, P. Prieto, Nanotechnology 2016, 27, 365708. [34] Y. Geng, S. Jun Wang, J. Kim, J. Colloid Interface Sci. 2009, 336, 592. [35] X. Wang, W. Dou, Thermochim. Acta. 2012, 529, 25. [36] L. Pavessi, M. Guzzi, J. Appl. Phys. 1994, 75, 4779. [37] A. Klamt, J. Phys. Chem. 1995, 99, 7, 2224–223. [38] J. R. Reynolds, B. C. Thompson, T. A. Skotheim, Conjugated Polymers: Properties, Processing, and Applications, Chapter 15, CRC Press – Taylor & Francis Group, Boca Raton, 2019, pp. 1–30. ChemistrySelect 2020, 5, 11737 – 11744 [39] Z. Wang, U. Wille, E. Juaristi, Encyclopedia of Physical Organic Chemistry Chapter 16, John Wiley & Sons, Hoboker, New Jersey, 2017, pp. 697–730. [40] K. Paduszyński, Phys. Chem. Chem. Phys. 2017, 6, 11835–11850. [41] J. A. Van-Vechten, T. K. Bergstresser, Phys. Rev. B. 1970, 1, 3351. [42] I. Vurgaftman, J. R. Meyer, L. R. Ram-Mohan, Appl. Phys. 2001, 89, 5815. [43] A. V. Talyzin, G. Mercier, A. Klechikov, M. Hedenström, D. Johnels, D. Wei, D. Cotton, A. Opitz, E. Moons, Carbon 2017, 115, 430. [44] S. Park, R. S. Ruoff, Nat. Nanotechnol. 2009, 4, 217. [45] L. Tang, X. Li, R. Ji, K. S. Teng, G. Tai, J. Ye, C. Wei, S. P. Lau, J. Mater. Chem. 2012, 22, 5676. [46] W. M. Qiao, Y. Song, M. Huda, X. Zhang, S. H. Yoon, I. Mochida, O. Katou, H. Hayashi, K. Kawamoto, Carbon 2005, 43, 3002. [47] A. Ejigu, K. Fujisawa, B. F. Spencer, B. Wang, M. Terrones, I. A. Kinloch, R. A. W. Dryfe, Adv. Funct. Mater. 2018, 1804357, 1. [48] B. Koo, S. Byun, S. W. Nam, S. Y. Moon, S. Kim, J. Y. Park, B. T. Ahn, B. Shin, Adv. Funct. Mater. 2018, 1705136, 1. [49] E. Istif, J. Hernández-Ferrer, E. P. Urriolabeitia, A. Stergiou, N. Tagmatarchis, G. Fratta, M. J. Large, A. B. Dalton, A. M. Benito, W. K. Maser, Adv. Funct. Mater. 2018, 1707548, 1. [50] Y. Gao, Y. Wan, B. Wei, Z. Xia, Adv. Funct. Mater. 2018, 1706721, 1. [51] S. Wang, F. Gong, S. Yang, J. Liao, M. Wu, Z. Xu, C. Chen, X. Yang, F. Zhao, B. Wang, Y. Wang, X. Sun, Adv. Funct. Mater. 2018, 1801806, 1. [52] Y. Jiang, Z. Xu, T. Huang, Y. Liu, F. Guo, J. Xi, W. Gao, C. Gao, Adv. Funct. Mater. 2018, 1707024, 1. [53] D. Joung, S. I. Khondaker, Phys. Rev. B. 2012, 86, 235423. Submitted: June 22, 2020 Accepted: September 25, 2020 11744 © 2020 Wiley-VCH GmbH