Impact of Rolled Graphene Oxide Grown on Polyaniline for Photodetection: Future Challenging Opto-Device

Abstract

Rolled graphene oxide (roll-GO) with anew morphological properties than normal graphene is synthesized using modified Hummer. Then, the roll-GO/PANI composite is prepared through the adsorption of roll-GO on the surface of the PANI film, that performed through the oxidative polymerization method. The developed composite displays a small bandgap of 1.9 eV and shows a high optical property extends through a wide optical region from UV to IR regions. The chemical structure and function groups are confirmed using the XRD and FTIR. The roll-GO/PANI composite was investigated as a photodetector. The effects of different irradiation light conditions and the monochromatic wavelengths were tested through the measurements of the produced current density, J_ph. The optical photon response exhibited excellent light sensitivity of the photodetector. The J_ph enhanced highly under light (0.34 mA·cm⁻²) compared to dark conditions (0.007 mA·cm⁻²). J_ph reached 0.24, 0.23, 0.14, and 0.09 mA·cm⁻² under 340, 440, 540, and 730 nm, respectively. The photodetector detectivity (D) and photoresponsivity (R) are found to equal 0.45 × 10⁹ Jones and 2.25 mA·W⁻¹, respectively.

1. Introduction

Recently, research in photodetector development has gained intense interest. These devices’ relevant properties extend their application in several domains [1,2,3]. Photodetector effectiveness relies enormously on the current density (J_ph) essentially associated with its working principle. Therein, each activated photon reaching the surface will liberate a hot electron capable of polarizing the surface resulting in a J_ph. This explains the high dependency of J_ph on the light intensity and consequently the assigned resonance motion. On the other hand, photodetector characterization i.e., photoresponsivity (R) and detectivity (D) of the light flux, show high dependency to the J_ph, specifying such a device’s effectiveness [4,5,6].

In this regard, inorganic materials i.e., metal oxide, sulfide, nitrides, or carbon materials, become major material candidates for use in photodetectors’ preparation. Such materials are challenging, since they demonstrate their photo-response by controlling two main factors: increasing active sites and modifying their surface area. The first factor is associated with the detection principle, relying on the accepted photon via materials/active sites, wherein the increase of these sites will consequently improve the photo-response. The second factor is related to the reshaping of the material into different forms i.e., nanosheets or nanorods [7,8,9,10,11,12].

Several studies on inorganic materials such as CuO, ZnO-CuO, CdS, ZnO, and carbon derivatives demonstrate the improvement of the materials at issue [11,12,13,14,15]. However, this material efficiency was limited and did not exceed 1% [10]. This encourages the association of oxides, sulfides, and nitrides materials with other components, like polymers [16,17]. Such a mixture exhibits a cost-effective, facile synthesis, good stability, sensitivity, and composite contacts as photodetectors [18,19]. Indeed, polymers demonstrate a promising photo-answer. Particularly, polyaniline materials are used as photodetector-based material [15]. Nevertheless, the obtained J_ph about 0.01 mA [16]. Other studies reveal the improvement of the optical properties while using aniline derivatives, such as benzodithiophene/fluorine [17]. Nevertheless, a remaining obstacle still facing polymers’ applications as photodetectors involves getting better J_ph and covering more than one optical set, i.e., UV, Vis, and IR, with good reproducibility.

Herein, rolled graphene oxide grown on PANI composite was prepared for photodetector application. The in-situ polymerization technique was used to deposit PANI on glass substrates, and then roll-GO was adsorbed on PANI. The roll-GO/PANI composites were studied using various characterization techniques. The CHI608E PowerStation was used to get the electrochemical measurements. It is looked at how the reproducibility current and light with wavelengths ranging from 340 to 730 nm affected the results. It has been established that light sensing has a reasonable mechanism. This promising photodetector displays a high ability of light detection in the different spectral domains. With great repeatability, the optoelectronic gadget responded to light well under on/off light.

2. Experimental Part

2.1. Materials

Pb(NO₃)₂, HCl, ammonium persulfate (((NH₄)₂S₂O₈), and aniline were obtained from Winlab, Watford, UK. H₂SO₄, Graphite powder, Na₂S, KMnO₄, H₃PO₄, and H₂O₂ from El-Naser Co, Cairo, Egypt.

2.2. Preparation of PANI

The preparation of PANI is demonstrated through polymerization method on the glass surface, in which HCl is applied as electrolyte and acid medium, and then the oxidant ((NH₄)₂S₂O₈) was dissolved. The polymerization process occurs under the direct addition of oxidant over the aniline monomer, and the appearance of the green color principate. Therefore, the polymer film is washed well and dried at 60 °C for 6 h.

2.3. Preparation of Roll-GO/PANI

The GO/PANI was prepared through physical adsorption of GO on the PANI surface. PANI film is then dipped in GO solution (50 mL, 11 mg/mL, and pH 6). This process remains for 3 h, though this time, the GO material is well adsorbed on the PANI surface.

The modified Hummer method is applied; 1.0 g of graphite is dissolved well in H₂SO₄ (99.9%) and H₃PO₄ (99.9%). Thence, KMnO₄ (6.0 g) is added to the mixture. This reaction causes the oxidation of these sheets and the formation of GO. The pH of this suspended solution increases to 6 through the decapitation washing process.

The rolling of graphene oxide has been synthesized via the agglomeration of GO sheets. This behavior appears clearly after letting the suspended solution stand for more than one week. The first sheet is rolled, then the other sheets are collected, resulting in the rolled graphene oxide materials (roll-GO).

2.4. Characterization Process

XRD analysis (PANalytical Pro, Almelo, Netherlands) and FTIR measurements verified the prepared composite chemical structure through the functional groups (FTIR, 340 Jasco spectrophotometers, Tsukuba, Japan). An absorbance spectrophotometer (Birkin Elmer, OH, USA) was utilized to examine the optical properties. On the other hand, the sample morphology was inspected through SEM (TEM) devices ZEISS, Oberkochen, Gemany (JEOL JEM-2100).

2.5. The Electrical Testing

The electrical testing of the roll-GO/PANI was performed with an electrical workstation (CHI608E) using 100 mV·s⁻¹ (Figure 1). We utilized a metal halide lamp (400 W, China) as a photon emitting system. For increasing the conductivity, a silver paste is performed on each side of the roll-GO/PANI film for anode and cathode connection. The experimental study is performed under different light conditions through exposure the photodetector to various monochromatic wavelengths.

3. Results and Discussion

3.1. Analyses

The SEM measurements demonstrate a highly porous network for PANI with high surface uniformity (see, Figure 2a). The porosity properties associated with the small particle sizes favor the use of this material for new composite formation [18,19]. The particle size average is about 110 nm. Once the composite has formed with roll-GO, the morphology changes to a high degree for powder- and thin-film-roll-GO/PANI composites, respectively (see Figure 2b,c). Roll-GO is to cover the surface of the PANI material; this roll-GO displays a high surface area having average dimensions of 250 nm in width and 2 m in length. The roll-GO is opened from its internal side, which ensures an increase of the surface area to higher degree. The new composite material, roll-GO/PANI is expected to have promising optical properties derived from the excellent light absorbance properties known for both PANI and roll-GO materials.

The theoretical face and cross-section of the roll-GO/PANI composite are calculated using the Gwydion program (see, Figure 2d). The formation of roll-GO over the polymer surface has been clearly distinguished. Such a rolled behavior of the GO materials will substantially increase the surface area.

The morphologies of the roll-GO is also confirmed (dark section) inside the 2D GO sheets through TEM measurements (see, Figure 3a). The rolled behavior of GO appears well through the dark rolled graphene oxide. Furthermore, an additional unrolled 2D sheets has also been located.

After the composite formation with PANI, the rolled behavior has again been demonstrated, wherein PANI materials appear as dark colors inside the formed rolled sheets. Moreover, the 2D behavior of GO is still present and PANI covers these sheets. This large surface area of roll-GO and PANI qualifies the prepared composite for optical applications. Indeed, the prepared photodetector is expected to have a good detection for broad optical regions, including UV, Vis, and near IR domains related to both GO and PANI material.

Figure 4a represents the optical properties of PANI and roll-GO/PANI. The roll-GO/PANI composite demonstrates a good optical property rather than the PANI material alone due to its improved composition gathering both PANI and roll-GO materials’ properties. The absorbance covers the UV, Vis, and IR regions, with an optimum absorbance peak at 310 and 650 nm assigned to electron transition under the photon incidence [20,21,22]. The broad absorbance peaks extending across almost the entire optical region reflect the great optical behavior for this nanocomposite. Particularly, the reaching of the absorbance peaks near IR regions is attributed to the electron vibration under the effect of IR radiation. Such magnificent optical properties evidence the high ability of roll-GO/PANI for light detection across broad optical regions.

The band gap of the prepared PNAI and roll-GO/PANI composite has also been tried (see, Figure 4b). The calculation depends on the Tauc equation (Equations (1) and (2)) [23], where h, $\mathrm{A},\mathsf{\alpha },\mathrm{and}\mathsf{\nu }$ represent the Planck constant, absorbance, absorption coefficient and the frequency, respectively. Using this equation and Figure 4b, the PANI and roll-GO/PANI bandgap values have been found equal to 2.5 and 1.9 eV, respectively. These results demonstrate the improvement in optical characteristics following the composite formation using roll-GO.

$$\mathsf{\alpha }\mathrm{h}\mathsf{\nu }=\mathrm{A}{\left(\mathrm{h}\mathsf{\nu }-{\mathrm{E}}_{\mathrm{g}}\right)}^{1/2}$$

(1)

$$\mathsf{\alpha }=\left(\frac{2.303}{\mathrm{d}}\right)\mathrm{A}$$

(2)

Using the FTIR (see, Figure 4c). The function’s groups are: C-N, N-H, and C-H bands, located at 1103, 3400, and 2917 cm⁻¹, while the C=C benzenoid and C=C quinoid appear at 1302 and 1468 cm⁻¹, respectively. After the roll-GO is adsorbed, additional functional groups of Epoxide groups of O-H and C-O were observed at 3400 and 1155 cm⁻¹, respectively. Moreover, extra small shifts of the PANI group were under this nanocomposite formation [24].

The chemical structure PANI and roll-GO/PANI has been investigated using XRD measurements (see, Figure 4d). PANI material has a semi-sharp peak signature from the semi-crystalline behavior of this material. In the nanocomposite, the XRD curve exhibited a sharp peak at 11° for the growth direction (001). This peak establishes the high crystalline nature of roll-GO materials [25]. Moreover, after the roll-GO composite, the crystalline nature of all composites i.e., roll-GO/PANI increases.

Figure 4. (a) Optical, (b) bandgap, (c) FTIR, and (d) XRD of PANI and roll-GO/PANI materials.

Figure 4. (a) Optical, (b) bandgap, (c) FTIR, and (d) XRD of PANI and roll-GO/PANI materials.

3.2. Electrical Study

The electrical testing of the prepared roll-GO/PANI for light sensing, i.e., as photodetector, was examined under a metal halide lamp (400 W). This study was measured using the electrochemical workstation (CHI698E. The light sensitivity was confirmed through the studies of on/off light conditions, and the applied monochromatic wavelengths on the prepared photodetector.

The effect of light and dark conditions on the roll-GO/PANI photodetector is reported in Figure 5a. The response and sensitivity of the roll-GO/PANI to the photons appear through the J_ph values decrease from 0.34 to 0.07 mA·cm⁻² (at 2.0 V), respectively. The J_ph value is produced through the hot generated electrons clouds on roll-GO materials, in which the incidence photons splits the associated energy levels. Finally, the electrons form a cloud on the conduction band of the roll-GO materials, identifying the J_ph values. The greater the J_ph value, the higher is the sensitivity of the roll-GO/PANI to the incident photons [26,27].

Moreover, Figure 5a illustrates the stability of the prepared roll-GO/PANI photoelectrode that repeats the current-potential relation under the light (repeating three times). Through this study, the produced J_ph shows almost the same values. Therefore, the prepared photoelectrode has a high sensitivity, as well as a high reproducibility of photon detections. The negligible effect of the external atmosphere appears on the photoelectrode through the small difference in J_ph values. This is could be assigned to the effect of the oxidizing and the active gases (i.e., O₂, NO₂, and CO₂) from the ambient atmosphere [28].

On the other hand, Figure 5b similarly confirms the stability and reproducibility of the roll-GO/PANI as to the incident photons, which under off/on chopping light, affect the J_ph values are 0.01 and 0.11 µA·cm⁻², respectively. These phenomena vary periodically under off/on chopped light, while J_ph values changes could be neglected. Indeed, the high absorbance of the prepared roll-GO/PANI materials in various optical regions reflectes well the highly the sensitivity to incidence photons. Thus, the prepared photodetector demonstrate a potential ability of light detection in broad optical regions extending from UV to near IR regions [29].

The sensitivity of the prepared roll-GO/PANI photodetector to the incidence light is illustrated through the monochromatic wavelengths’ effect on this electrode. This study is applied using various monochromatic wavelength filters: 340, 440, 540, and 730 nm during the light passage within the photodetector. Herein, different J_ph values, 0.24, 0.23, 0.14, and 0.09 mA·cm⁻² under 340, 440, 540, and 730 nm, respectively, have been obtained (see Figure 6a). On the other hand, Figure 6b illustrates J_ph values at 2.0 V, where wide regions extending from the UV to IR for the photodetector have been located, confirming the amazing sensitivity of the photodetector. The photodetector answer in the UV region originated by the light of high frequency assigned to the electrons transition, while its response near the IR region is produced under the electron vibration under the light effect. Indeed, this demonstrates the high ability of the repaired photodetector in generating a great number of photoelectrons under photon illumination [30,31] which make it promising for industry.

The observed behavior and efficiency of the prepared roll-GO/PANI photodetector to the incidence photons in the broad optical regions extending from UV to near IR are calculated by measuring the photoresponsivity (R) and detectivity (D).

Equation (3) [32] represents the relation of R, in which this relation depends on the (J_ph) and dark (J_o) conductions with the consideration of light density (P).

$$\mathrm{R}=\frac{{\mathrm{J}}_{\mathrm{ph}}-{\mathrm{J}}_{\mathrm{o}}}{\mathrm{P}}$$

(3)

$$\mathrm{D}=\mathrm{R}\sqrt{A /2{\mathrm{e}\mathrm{J}}_{\mathrm{o}} }$$

(4)

Figure 7a represents the R-value for the roll-GO/PANI photodetector from UV to near-IR region. The photodetector demonstrates an R-value of 2.25 mA·W⁻¹ in the UV region (340 nm) that decreases with the increasing of the wavelengths to reach 1.15 mA·W⁻¹ in the IR region (730 nm). The good R-value in the UV and Vis regions reflect the high response of the photodetector to the incident photons, one which causes activation of the energy levels and the electron transition to the conducting bands of roll-GO/PANI materials. This effect increases the J_ph value and then the R values. The high R-value in all the optical regions from 340 to 730 nm confirms the great application of this prepared photodetector to light detection in these wide optical regions with high efficiency.

On the other hand, the D values for the prepared photodetector have the same manner; this value is calculated using Equation (4) [33]. The D values depend on the R, A, and e, in which A is active surface are under the electron heneration (e) process. The photodetector has great D value at 340 nm (0.49 × 10⁹ Jones). The D value decreases with increasing wavelengths, in which this value reaches 0.3 × 10⁹ Jones in the IR region (730 nm). The elevated D values in all the optical regions from 340 to 730 nm, confirm the high photosensitivity for this promising nanocomposite photoreactor.

The photodetector has a great sensitivity for light detection in a wide optical spectra. This also has been illustrated through a comparative study of prepared roll-GO/PANI to earlier ones, as mentioned in

Table 1. The performance of the photodetector in comparison with published literature.

Photodetector	Wavelength (nm)	Bais (V)	R (mAW−1)
Graphene/P3HT [34]	325	1	NA
GO/Cu2O [35]	300	2	0.5 × 10−3
diazole polymer [17]	734	0	NA
polymer/CsPbBr3 [22]	500	2	NA
Graphene/GaN [36]	365	7	3 × 10−3
ZnO-CuO [37]	405	1	3 × 10−3
GO/Cu2O [35]	300	2	0.5 × 10−3
ZnO/Cu2O [38]	350	2	4 × 10−3
CuO nanowires [39]	390	5	-
TiN/TiO2 [10]	550	5	-
CuO/Si Nanowire [40]	405	0.2	3.8 × 10−3
TiO2-PANI [41]	320	0	3 × 10−3
Se/TiO2 [42]	450	1	5 × 10−3
ZnO/RGO [43]	350	5	1.3 × 10−3
TiO2/NiO [44]	350	0	0.4 × 10−3
Roll-GO/PANI (this work)	440	2	2.25

.

3.3. Mechnaism of Rolling up the GO Material

Figure 8 demonstrates the general mechanism for obtaining the rolling of graphene oxide. In general, the rolling process for most materials is obtained through few steps [45]. Indeed, after the preparation of 2D GO via the modified Hummer method (Figure 8a), the obtained sheets are naturally folded while being long time in the solution (Figure 8b). Such a folding process represents the actual steps finally transforming the two dimensional (2D) graphene sheets into a three dimensional (3D) rolled graphene sheets (Figure 8c). This obtained roll-GO is similar to the carbon nanotubes.

4. Conclusions

Roll-GO/PANI are demonstrated and applied as a photodetector in a wide optical region covering UV to IR. Highly rolled graphene oxide sheets have been prepared through GO sheets agglomeration (one week after preparation). The composite is formed by rinsing the PANI film inside the roll-GO suspended solution. XRD and FTIR confirm the functional groups in the prepared composite. The composite bandgap was found to be 1.9 eV; this small bandgap is related to the great optical absorbance that extends from the UV to the IR regions. The constructed photodetector has a high sensitivity to light photons, and in dark and light circumstances, respectively, the J_ph value increases from 0.007 to 0.34. Also, this photodetector displays a strong photo-response to the monochromatic wavelengths; the J_ph values are 0.24, 0.23, 0.14, and 0.09 mA·cm⁻² under 340, 440, 540, and 730 nm, respectively. Moreover, the efficiencies are 2.25 mA·W⁻¹ and 0.45 × 10⁹ Jones for R and D values, correspondingly. These properties confirmed the future potential application of this photodetector the commercial industrial field.