Introduction

The doping of inorganic nanoparticles into conductive polymer matrix can provide high performance and efficient novel materials that find applications in dye-sensitized solar cells, short-wavelength organic light emitting diodes, transparent conductors, gas sensors and piezo-electric materials, etc. [1]. In recent years much research efforts have been directed towards the investigation on conductive polymers. As a consequence, conductive polymers have grown to be very important in various applications such as fuel cells, electrochemical cells, display devices, memories and sensors [2]. It is reported that the incorporation of inorganic nanoparticles into polymers matrix enhances the optical, structural as well as electrical properties. Reduction of the gas permeability and humidity of the conductive polymer matrix is also observed [3]. The development of nanostructured materials for its uses in nanoscale devices has been extensively expanding [4]. Because of the quantum confinement and increment of surface to volume ratio, it can show the properties of nanomaterials that are drastically different from the bulk counterparts [5]. The presence of inorganic nanoscaled additives in polymer matrix has been proved to enhance the optical and electrical properties [6].

Polyvinyl alcohol (PVA) is a polymer with exceptional properties such as high dielectric strength (> 1000 kV/mm), water solubility, biodegradability, biocompatibility, non-toxicity, good charge storage capacity, dopant-dependent electrical property and non-carcinogenity that possesses the capability to form hydrogels by different methods [7,8,9,10]. The outstanding chemical resistance, physical properties, and complete biodegradability of PVA pave the path for its broad practical applications [11]. As a consequence, PVA has grown to be important in various applications, such as electrochemical cells, fuel cells, display devices, memories and sensors [12,13,14]. PVA film can be easily prepared by solution casting method due to its water solubility property [15].

On the other hand, Zinc oxide (ZnO) is basically a II–VI group semiconducting material with wide band gap energy 3.2–3.4 eV [16, 17] at room temperature. ZnO has been the subject of enormous studies in the last few decades because of its exciting properties, such as resistivity control, direct band gap, transparency in the visible wavelength region, high electrochemical stability, absence of toxicity and abundantly available in nature [18]. In this context, zinc oxide (ZnO) nanostructured materials have gained much of interest as it shows good electrical and optical properties which have led to its wide use in a variety of industrial and technological applications in chemical sensors, piezo-electric films, surface acoustic wave devices, catalytic action and photovoltaic applications [19, 20].

Polyvinyl alcohol (PVA), a degradable polymer, is easily dissolved in solvents [21] like distilled water and ethanol. Also the synergistic combination of ZnO nanoparticles and PVA results in improved structural, electrical, and optical properties. This is probably due to its effective functional group and the backbone structure of PVA–ZnO composite [22]. ZnO-based PVA nanocomposites prepared by various physical and chemical methods such as solvent or solution casting, in situ method, chemical vapor deposition, vapor–liquid–solid growth process, melt processing methods have been extensively employed to design, fabricate and obtain the desired matrix of PVA–ZnO nanocomposites [23, 24].

Thus, using polymeric PVA–ZnO nanocomposites, one can successfully fabricate novel hybrid materials with low band gap, high dielectric permittivity, high breakdown voltages and energy storage density for applications in sensors, OLEDs and capacitors as electric energy storage devices. Investigation on the incorporation of inorganic particle into polymer matrix has been developed by many researchers. Hemalatha et al. reported the structural and optical properties of PVA–ZnO nanocomposites [25]. They also discussed about the luminescence properties of films with different excitation wavelengths. Further B. Karthikeyan et al. studied the time resolved photoluminescence of PVA–ZnO nanocomposite films [26]. Concentration-dependent structure, optical and electrical properties of PVA–ZnO nanocomposite films prepared via in situ techniques have not been investigated in detail. The present study reports the synthesis, characterization and concentration-dependent performance evaluation of the structural, optical and electrical properties of PVA–ZnO nanocomposite films as electron transport material, synthesized in the laboratory.

Experimental

Materials

Poly vinyl acetate (Molecular weight ~ 124,800) (Merck) with high purity, sodium sulfate (Na2SO4) (molecular mass = 142.05 g/mol) (Merck), sulfuric acid (H2SO4) (Merck) (molecular mass = 98.08 g/mol), zinc nitrate hexahydrate (molecular mass = 297.47 g/mol) (Merck) and sodium hydroxide (molecular mass = 39.99 g/mol) (Merck) were procured for synthesis purpose. Deionised water and methanol (Merck) were used as solvents during chemical processing.

Synthesis of PVA

PVA powder was prepared via co-precipitation technique. In this method, polyvinyl acetate was coagulated from its emulsion using a solution of sodium sulfate in the presence of methanol as solvent and distilled water. 100 mg of polyvinyl acetate emulsion (60% by weight solid content) was stirred with 25 ml methanol, and it was dissolved in the aqueous solution of sodium sulfate salt (100 mg Na2SO4 and 100 ml distilled water) and 1 ml sulfuric acid in a conical flask. The mixture was stirred for 2 h at temperature in the range 30–50 °C. The reaction mixture was allowed to settle for about 1 h at room temperature. The polyvinyl acetate was coagulated and three layers were formed: the top layer was emulsifiers, the intermediate (middle) layer was liquid phase (water, dissolved salt, and methanol), and the bottom layer was the precipitated polymer. The collected precipitate was then washed three times with distilled water and filtered. The resulting polymer consisted of 75–80% polymer and 20–25% water. The polymer mixture was dried in an oven at 50 °C for 24 h to obtain the PVA powder.

Synthesis of PVA–ZnO nanocomposites

In situ method was used for the fabrication of nanocomposite films. Firstly, 5 mg PVA stock solution was prepared by dissolving PVA powder into 15 ml distilled water under constant heating up to 75 °C for 2.5 h. The ZnO:PVA nanocomposites were prepared in varying concentrations of zinc nitrate hexahydrate (1,2 and 3 mg) by dispersing it into 5 mL of double distilled water separately and then NaOH or KOH (0.5 M) was added to the solution. The solution was mixed under continuous stirring for 5 h. Afterwards, 5 g PVA stock solution was added to it and stirred vigorously using magnetic stirrer until transparent PVA–ZnO multicomponent dispersion was obtained. Each concentration of PVA–ZnO composite was poured in a petri dish and was dried in a dust-free chamber at room temperature for about 72 h to obtain the nanocomposite films. The schematic representation of as-synthesized PVA and PVA–ZnO nanocomposite has been shown in Fig. 1.

Fig. 1
figure 1

Schematic diagram of the as-prepared PVA and PVA–ZnO nanocomposites

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Characterization

The as-synthesized PVA and PVA–ZnO nanocomposites were characterized by X-ray diffractometry (XRD-GBCMMA, Cu-Kα radiation, λ = 1.5406 Å). The XRD patterns were recorded in the 2θ angular range 10°–70°. The FTIR spectroscopic (Perkin Elmer-RX1) analysis of PVA and PVA–ZnO composites was carried out in the frequency range 4000–400 cm−1 using KBr pellet techniques. Field emission scanning electron microscopy (ZEISS, SUPRA-55) was used to investigate the surface morphology of these films. Optical absorbance and band gap of these films were examined by UV–Vis spectroscopic technique (CARY-5000) in the wavelength range 200–800 nm. The thickness of these films was measured by US Mprobe VIS spectroscopic reflectometer (Mprobe-20 series). The photoluminescence spectra were recorded using fluorescence spectrophotometer (Hitachi F-2500 Fluorescence Spectrophotometer) at the excitation wavelength of 250 nm. The Film roughness and surface morphology of pure PVA and PVA–ZnO composites of varying concentrations were examined by atomic force microscopy (Bruker) using tapping mode. The J–V characteristics of the said films were studied by source meter (KEITHLEY 2400).

Results and discussion

XRD analysis

To examine the structure of the polymer composite films, X-ray diffraction spectroscopic technique was employed. Figure 2 shows the XRD spectra for pristine PVA and PVA–ZnO nanocomposite films of varying concentrations. The XRD spectra for pristine PVA shown in Fig. 2a revealed the relatively strong broad diffraction peak located at 2θ = 20.04°. This corresponded to (101) reflection plane of PVA and a greater peak at 41.9° indicated the semi-crystalline nature of PVA [27,28,29,30]. There was a strong intermolecular interaction between PVA chains through hydrogen bond which confirmed the semi-crystalline nature of PVA [31].

Fig. 2
figure 2

XRD pattern for a pristine PVA, b JCPDS card no. (36-1451), c–e PVA–ZnO nanocomposites of varying concentrations

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The X-ray diffraction pattern of PVA–ZnO nanocomposites has been shown in the Fig. 2c–e. The corresponding diffraction peaks matched with the diffraction peak of PVA and standard PDF database (JCPDS 36-1451) of ZnO wurtzite hexagonal crystal structure [32]. These diffraction peaks confirmed the formation of PVA–ZnO nanocomposite with the increase in crystallinity of PVA matrix with the embodiment of ZnO nanofiller. There were some additional peaks instead of PVA and ZnO peaks. This structural deformation was due to the variation in inter-planar spacing, lattice parameters, concentration of defects, development of micro-strain and crystallite size in crystal structure due to the host PVA matrix [33]. Lattice parameter and unit cell volume of PVA–ZnO nanocomposites were calculated and shown in Table 1.

Table 1 Data of lattice parameter and unit volume for PVA–ZnO nanocomposites of varying concentrations
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Relation of d-spacing and crystallite size as function of concentration ratio

The crystallite size of the synthesized nanocomposites was calculated using Scherer’s formula [34] as shown by the relation:

$$ D = \frac{K\lambda }{{B\,{\text{Cos}}\theta }} $$
(1)

where D is the average crystallite size, λ is the wave length of X-ray (1.5416 Å), B is the full-width of half-maximum of a diffraction peak in radian, θ is the diffraction angle, and K is the Scherrer’s constant of the order of unity for usual crystal (0.9). The d spacing (d) of the lattice was calculated by the Bragg’s law as shown by the following relation [35]:

$$ \lambda = 2d\,{\text{Sin}}\theta $$
(2)

The concentration-dependent study of d-spacing and crystallite size of PVA–ZnO nanocomposites has been shown in Fig. 3a. A meager shifting of peak was observed towards lower scattering angle for all the concentrations. The highest optimized crystallographic lattice (~ 2.37 Å) was found for the PVA:ZnO (5:2) ratio due to fair dispersion of the ZnO nanofillers in the polymeric surface, which led to an increase in interfacial adhesion between the filler and polymeric matrix [36]. The crystallite size of nanocomposites was increased due to decrease in the peak width or FWHM (full-width half-maxima) value. The highest optimized crystallite size was observed for the PVA:ZnO (5:2) ratio due to the relative increase in ZnO nanofillers population during crystallization process.

Fig. 3
figure 3

a Crystallography lattice and crystallite size as a function for PVA:ZnO nanocomposites of varying concentrations, b FWHM and crystalline index as a function of PVA and PVA:ZnO nanocomposites of varying concentrations

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Relation of FWHM (full-width half-maxima) and crystallinity (%) with PVA and PVA:ZnO nanocomposites

The crystallinity (%) of polymeric nanocomposite was calculated by the following relation [37]:

$$ {\text{Crystallinity}}\left( \% \right) = \frac{{{\text{Total}}\;{\text{integrated}}\;{\text{area}}\;{\text{of}}\;{\text{crystalline}}\;{\text{peaks}}}}{{{\text{Total}}\;{\text{integrated}}\;{\text{area}}\;{\text{of}}\;{\text{all}}\;{\text{peaks}}}} \times 100\% $$
(3)

Figure 3b presents the correlation of FWHM (full-width half-maxima) and crystallinity index with respect to pure PVA and PVA:ZnO nanocomposites of varying concentrations. The pristine PVA showed the broad diffraction. With the incorporation of ZnO fillers in PVA polymeric matrix, a relatively lower value of FWHM was examined due to the reduction of point defect in pristine PVA [38]. The optimized lowest value of FWHM (~ 0.9411°) was observed for PVA:ZnO (5:2) ratio due to the proper alignment of ZnO on the PVA surface. There was small change in crystallinity index observed with the incorporation of ZnO nanofillers and optimized higher crystallinity (%) (~ 61.94) was observed for PVA:ZnO (5:2) ratio, due to the well distribution of ZnO nanofillers on PVA surface.

FTIR analysis

The FTIR spectrum for pure poly vinyl alcohol and PVA–ZnO nanocomposites has been depicted in Fig. 4. The FTIR transmission spectra confirmed the interaction between polymer and metal oxide over the wave number range 500–4000 cm−1 in KBr medium. The peaks appeared in the higher wavenumber side were ascribed to the vibration of organic compounds of PVA matrix. Absorption peaks in the wave number around 500 cm−1 in the PVA–ZnO nanocomposites occurred due to Zn–O stretching which was not observed in the pure PVA film. This confirmed the presence of ZnO in PVA matrix. The absorption peaks recorded at 1444, 1108 and 840 cm−1 were assigned to the vibrations of CH2, C–C and C–H modes, respectively. The peak recorded around 1570 and 1660 cm−1 could be assigned due to the C=C bond and C=O stretching vibration, respectively. Whereas absorption peak at 1440 cm−1 was related to C–H deformation mode. Peaks around 2935, 920 cm−1 are suggested to the characteristic –CH2 stretching and bending vibration bands of PVA, respectively. The peak around 1255 cm−1 was just because of C–C stretching or from wagging vibration of CH. The peaks having wavenumber 1065 cm−1 are due to (C–O) stretching vibration of the ether group. The peaks which were observed between 2918 and 2659 cm−1 were symmetric and asymmetric C–H2 bond’s osculation. A peak at 1023 cm−1 corresponded to C–O–C stretching of acetyl group present on PVA backbone. On comparing the absorption spectra of pure PVA and PVA–ZnO composites, the broad peak of pure PVA at 3432 cm−1 was shifted towards the higher wave number of about 3575–3587 cm−1. In the FTIR spectra of PVA:ZnO composite, the shift was due to the formation of intermolecular hydrogen bonds between O–H group of PVA with the surface of ZnO. This confirmed the light surface coating of PVA on ZnO nanoparticles.

Fig. 4
figure 4

FTIR spectra for PVA and PVA–ZnO nanocomposites of varying concentrations

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FESEM analysis

The surface morphology for pure PVA and PVA–ZnO nanocomposites has been shown in Fig. 5. The PVA–ZnO nanocomposites revealed the inclusion of ZnO nanowires on the surface of PVA. The FESEM image of PVA–ZnO nanocomposites confirmed that with the increase in the concentration of ZnO, crystallites were initiated and grown in the immediate vicinity of the surface. It also showed uniform dispersion of ZnO nanowires, whereas with the increase in the ZnO concentration, more compactness and aggregation existed. This showed the higher crystalline nature of the sample and the surface of the sample was more rough as compared to pure PVA supporting the observation of XRD and AFM analysis. The EDX (energy dispersive X-ray spectroscopy) spectrum of PVA–ZnO composite confirmed the successful incorporation of ZnO nanowires into polymer matrix.

Fig. 5
figure 5

FESEM images for PVA and PVA–ZnO nanocomposites of varying concentrations and EDX spectrum of pure and nanocomposite sample

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Optical properties

UV–Vis spectroscopy analysis

UV–Vis absorption spectroscopic technique was employed to examine the optical properties of nano-sized particles and nanocomposite films. The absorption spectra of pure PVA and PVA–ZnO composites were recorded using double beam UV–Vis spectrometer and these have been shown in Fig. 6a.

Fig. 6
figure 6figure 6

a UV–Vis spectra for PVA and PVA–ZnO nanocomposites of varying concentrations. b The plot between (αhυ)2 versus hυ for PVA and PVA–ZnO nanocomposites of varying concentrations. c The plot between (αhυ)1/2 versus hυ for PVA and PVA–ZnO nanocomposites of varying concentrations. d Optical dielectric loss versus photon energy (hυ) for PVA and PVA–ZnO nanocomposites of varying concentrations

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The absorption peak of pure PVA was recorded with broad absorption band at 210 nm. This band arose due to semi-crystalline nature of PVA. Another reason was the presence of un-hydrolyzed acetate group and carbonyl containing structure which was connected to the PVA polymer matrix [25, 39]. These bands corresponded to the electronic transitions n–π* and π–π*, respectively [40]. The optical absorption spectra of PVA–ZnO composites film showed two bands appeared at 280 nm and further at 370 nm with less intensity which corresponded to the presence of ZnO in the film [41]. These bands were referred to the absorption of PVA and excitons of ZnO nanoparticles. The absorption edge of ZnO nanoparticle was 10 nm blue shift in comparison to the characteristic ZnO at room temperature. Such blue shift occurred due to the reduction in the crystallite size [42, 43]. As indicated in the UV absorption spectra, the higher the concentration of ZnO into PVA matrix, the better the absorbance of PVA host in the UV–Vis region. Thus, the absorption edge shifted towards the lower energy or higher wavelength associated with the blue–green region of the visible spectral range with increasing concentration of the nano-sized ZnO particle.

Determination of optical band gap

Optical band gap is the appropriate way to define the optical transition in nanocomposites film using Tauc’s plot [44]. The frequency-dependent absorption Coefficient has been shown by the relation:

$$ \left( {\alpha h\upsilon } \right)^{1/n} = B(h\upsilon - E_{\text{g}} ) $$
(4)

where α is the absorption coefficient, hυ is the energy of incident photon, B is the constant that depends on the inter band transition probability, E g is the optical band gap and n is the index characterizing the nature of the electronic transition which causes the optical absorption. We can take n as the value \( \frac{1}{2} \), \( \frac{3}{2} \), 2, 3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden electronic transitions, respectively. The absorption coefficient α is calculated using Beer–Lambert’s relation [45] as shown by the relation.

$$ \alpha = \frac{2.303A}{d} $$
(5)

where A is the absorbance and d is the thickness of the sample. The average thickness ‘d’ of nanocomposite films was calculated and shown in Table 2. Figure 6b, c shows the direct and indirect band gap value using the plots between (αhυ)2 versus hυ and (αhυ)1/2 versus hυ for pure PVA and PVA–ZnO nanocomposites, respectively. By extrapolating the line segment of the spectra to x axis, one can determine the optical band gap. The acquired values of band gap (E g) for both the electronic transition have been tabulated in Table 3. In the case of organic–inorganic mixture, nature of electronic transition was rather difficult to predict. The optical dielectric loss was another precise method to examine the exact value of optical band gap which confirmed direct or indirect nature of band gap [46] due to the direct response to incident photon to electronic transition [47]. The optical dielectric loss was calculated using imaginary part of dielectric constant (ɛ i ) using the following relation [48]:

Table 2 Average thickness data for PVA and PVA–ZnO nanocomposites of varying concentrations
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Table 3 Direct band gap, indirect band gap and band gap calculated from optical dielectric loss for PVA and PVA–ZnO nanocomposites of varying concentrations
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$$ \varepsilon_{i} = 2nK $$
(6)

where K is the extinction coefficient (\( \frac{\alpha \lambda }{4\pi } \)), α is the absorption coefficient, λ is the wavelength and n is the refractive index \( \left( { R = \frac{{\left( {n - 1} \right)^{2 } + K^{2} }}{{(n + 1)^{2} + K^{2} }}} \right) \), where R is the reflectance. Figure 6d shows the intersection of linear segment of optical dielectric loss on photon energy and it was almost matched with the direct band gap values. As a result, the direct allowed electronic transition \( \left( {n = \frac{1}{2}} \right) \) is possible for PVA and PVA–ZnO nanocomposites films.

It was confirmed from Fig. 6b that with the addition of ZnO nanoparticle in PVA matrix, direct optical energy gap decreased due to the p-type conductivity of nanocomposite film and the optimized band gap of sample 5:2 was about 2.985 eV. This occurred due to the formation of reinnovative new level in the band gap, and began to promote the electron move through valance band to local level to the conduction band. As a result, the band gap decreased and conductivity increased [49]. Another reason was the formation of donor level in the bottom of the conduction band which resulted in the tensile strain developed in the nanocomposite films [50].

Photoluminescence analysis

The photoluminescence emission spectra for pure PVA and PVA–ZnO nanocomposites under 250 nm excitation using xenon arc lamp as excitation source have been shown in Fig. 7. These exhibited luminescence emission in the blue region. There were two identifiable emission peaks appearing at near about 390 and 470 nm due to the radiative and non-radiative recombination of electron–hole pair in the nanocomposite film [51]. The emission peak observed at 390 was attributed to the band edge exciton radiative recombination of ZnO [52]. The emission peak near about 470 nm occurred due to the phonon-assisted transition [53]. Intense blue spectrum was ejected from the ZnO nanoparticle. From the photoluminescence spectra, the optimum luminescence intensity was found for 5:2 ratio of PVA–ZnO nanocomposites due to the increase in the electron–hole recombination rate. Although for 5:1 and 5:3 PVA:ZnO ratio, the emission intensity was lower. This occurred due to the self absorption of light and it was quite relevant to the data of UV–Vis absorption spectroscopy. Thus, the photoluminescence properties of nanocomposite films specified that it could be possibly used in organic light emitting diode as an organic electron transport layer.

Fig. 7
figure 7

PL spectra for PVA–ZnO nanocomposites of varying concentrations

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AFM analysis

The AFM technique reveals 3D profile of the surface on a nanoscale, by measuring forces between a sharp probe (< 10 nm) and surface at very short distance (0.2–10 nm probe-sample separation). It was basically used to evaluate the surface roughness, grain size of nanocomposite thin film and nanoscale topology [54].

Figure 8 shows the height sensing atomic force microscopy image of PVA and PVA–ZnO nanocomposites. The height of the tor was observed in micrometer range. It indicated the micro-domain structure of the surface. From Fig. 8, a clear heterogeneous structure was observed in the nanocomposite films due to the presence of crystalline materials in the semi-crystalline composite phase.

Fig. 8
figure 8

AFM images for PVA and PVA–ZnO nanocomposites of varying concentrations

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The height parameters calculated from the AFM image have been shown in the Table 4. From the above data, it was observed that with the increase in the concentration of ZnO nanoparticles, the average and RMS (root mean square) roughness increased and at the same time average length of the peak also increased. This occurred due to the strong interaction between the ZnO nanoparticle and PVA polymer macromolecule that eventually grasped the surface polymer chain to produce a renovated compact structure [55].

Table 4 AFM data for roughness parameter of PVA and PVA–ZnO nanocomposites
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Electrical properties

J–V measurement

The conductivity behavior of PVA and PVA–ZnO nanocomposite film of varying concentrations was measured at room temperature in the potential range − 10.0 to + 10.0 V as represented in Fig. 9. Figure 9 shows that the current increased linearly with increase in the applied voltage. This occurred due to the electron mobility which was completely based on electron–hole recombination process. There was an increase in minority charge carrier (hole) as compared to the majority charge carrier (electron) with the embodiment of ZnO into the PVA matrix. Based on this explanation, the conduction mechanism for these conducting polymer nanocomposites was quite different from that of intrinsic semiconductors [56]. The sample ratio of PVA:ZnO (5:2) exhibited the optimized higher current density of 12.1 µA/cm2. This occurred due to the increased neck particle size in PVA:ZnO (5:2) sample which formed wider neck between adjacent particles; hence, resistivity was decreased and recombination rate was increased. It is quite favorable for good electron transport due to the transfer of electrons from one particle to another through larger path width [57]. The enhancement of current density for optimized PVA:ZnO (5:2) ratio sample was observed 237.83% compared to pure PVA. These electrical properties specified that the said PVA–ZnO nanocomposite film could be used as an electron transport layer in OLED application.

Fig. 9
figure 9

J–V characteristics for PVA and PVA–ZnO nanocomposites of varying concentrations

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Conclusion

Polyvinyl alcohol (PVA) and PVA–ZnO nanocomposites of varying concentrations were successfully synthesized in the laboratory by co-precipitation and in situ methods, respectively. The XRD analysis showed confinement of ZnO in polymer matrix. The peak narrowing and peak shift associated with the XRD study exhibited crystallite size variation due to the structure deformation and growth of micro-strain. The FTIR studies confirmed the successful formation of PVA–ZnO nanocomposites. The FESEM images showed the appropriate size distribution of ZnO nanowires into the PVA polymeric surface, and smaller sizes of ZnO nanowires in lower concentration nanocomposites.

The UV–Vis measurements showed two bands at 280 and 370 nm which were attributed to the absorption of PVA and excitons of ZnO nanoparticles. The optical direct band gap decreased with the addition of ZnO nanoparticle and the optimum band gap was found 2.985 eV as inferred from the optical dielectric loss curve. The study showed that the light emitting property of ZnO was completely controlled by PVA through surface passivation. The film showed the optimum increases in PL (photoluminescence) intensity for (5:2) of PVA:ZnO ratio and exhibited ultraviolet luminescence and enhanced the optical property for OLED devices. The AFM analysis confirmed the heterogeneous structure in nanocomposites. It also showed that RMS roughness increased with the increase in concentration of ZnO. The electrical properties showed enhancement in current density (237.83%) as compared to pristine PVA and the optimized current density was found to be sample of PVA:ZnO (5:2) ratio due to the highest electron hole recombination rate which led to its application for OLED device fabrication as an electron transport layer.