New photodiodes based graphene-organic semiconductor hybrid materials

doi:10.1016/j.synthmet.2015.12.026

Synthetic Metals

Volume 213, March 2016, Pages 47-56

https://doi.org/10.1016/j.synthmet.2015.12.026 Get rights and content

Highlights

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Nanocomposites of graphene oxide doped with the coumarin diodes were fabricated.
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The transient photocurrent measurement indicates that the photoresponsivity is tunable by adusting GO:coumarin fraction.
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Al/GO:coumarin/p-Si/Au diode has a good potential as a photosensor.

Abstract

New photodiodes based graphene-organic semiconductor hybrid materials were fabricated for the first time using sol–gel spin coating technique. The current–voltage characteristics of the Au/GO:coumarin/p-Si/Al diodes were investigated under dark and various illumination intensities. The various junction parameters of the diodes were determined using I–V, C–V and transient characteristics. The transient photocurrent measurements indicate that Au/GO:coumarin/p-Si/Al diodes are very sensitive to illumination and the precise responsivity of the diodes is tunable by adjusting GO:coumarin fraction. The capacitance–voltage–frequency (C–V–f) measurements indicate that the capacitance of the diodes depends on voltage and frequency. The capacitance decreases with increasing frequency due to a continuous distribution of the interface states. The ability to tune the photosensitivity in the photoconductive mode through graphene oxide:coumarin weight ratio has been shown to lead to a near-constant sensitivity to illumination for a weight ratio of 0.03GO. The obtained results suggest that Au/GO:coumarin/p-Si/Al diodes can be used as a photosensor in optic communications.

Graphical abstract

Introduction

There is much research interest in graphene at present due to its unique electrical and optical properties. Graphene films are among the most favorable candidates for next generation transparent conductive electrodes [1], [2], [3]. Such electrodes have been studied widely over the past decade because of their potential applications in flat panel displays, metal/semiconductor diodes and many other electronic devices. In the present work, we have utilized semiconducting nanocomposites of coumarin–graphene oxide to fabricate the photodiodes. Coumarin and its derivatives have attracted considerable wide research interest in pharmaceuticals for their exciting UV–vis photoresponse properties and industry in the form of dye lasers and high-efficiency dye-sensitized solar cells. The molecules exhibit fluorescence in visible light range, large Stokes shifts, high quantum yields and good solubility [4]. Recent studies have focused on the structure vs. optical property of coumarin to better grasp the electronic operational mechanisms that could lead to better rational designs of more efficient coumarin derivatives for optical device applications [5], [6]. There have been a number of scaffolding organic compounds that have been used for a variety of reasons, such as low sheet resistance, high optical transparency. The later can be accounted for by fact that the hybrid electrode can overcome the low work-function and high sheet resistance [7], [8]. The coumarin molecule consists of a benzene ring fused together with a lactone ring whose double bond extends the conjugated π-system across the molecule. Conjugated coumarins with many of their derivatives, such as anthracene have been shown to possess the planarity required for rigid structure. This makes them suitable for development on flexible substrate. Their wide energy gaps and high fluorescent quantum efficiency makes them potential candidates for use in UV–vis photo-applications [9], [10]. The coumarin interlayer is thought to influence the space-charge region of the Schottky junction thereby increasing the barrier height. The electronic properties of coumarin have also been studied and it was found that increased reaction time leads to a lower sheet resistance on the film [11]. The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the coumarin–GO/p-Si junctions having various compositions of GO were studied under dark and illumination conditions. It was observed that the photocurrent of the device increases with increase of GO concentration in the composite. The non-illuminated ideality factors of the diodes having 0.005, 0.01, 0.03 and 0.1% of GO in the coumarin–GO composites were obtained to be 3.803, 4.095, 6.838, and 4.893 respectively. The diode having 0.03GO content consistently exhibited the highest photoresponse performance. The obtained results indicate that coumarin–GO composites have high potential in photosensor applications.

Section snippets

Experimental details

The graphene oxide (GO) was synthesized by modified Hummers method as described in the literature [12], [13]. The coumarin was dissolved in dicholoro benzene. The synthesized GO was dispersed in deionized water (1.5 mg/ml) using stirring for 10 min. and then, it was ultrasonicated for 2 h. The nanocomposites of coumarin and GO were prepared using coumarin and GO solutions having different weight ratios of GO:coumarin (0.005, 0.01, 0.03 and 0.1). The films of GO:coumarin were coated onto surface of

Results and discussion

Fig. 1(a–d) shows SEM images of the GO:coumarin films. As seen in Fig. 1(a–d), the surface morphology of the films is changed with GO contents. As seen in Fig. 1a, the composite is formed from the graphene oxide layer and coumarin capped GO layers. The graphene oxide was capped by coumarin organic layer.

Fig. 2(a–d) shows I–V characteristics of the Au/GO:coumarin/p-Si/Al diode under dark and various illumination intensities and GO concentration. The ability to tune the photosensitivity in the

Conclusions

Organic on inorganic p-Si Schottky diodes with the structure Au/GO:coumarin/p-Si/Al have been fabricated for the first time. The device parameters were evaluated using current-voltage, capacitance–voltage and phototransient methods with respect to the fraction of graphene-oxide to coumarin ratio. These measurements indicate that the Schottky diode is sensitive to light and there exists the possibility to optimize its performance based on the content of GO. The tunability of the device

Acknowledgment

Three of the authors (AM, KH & FY) would like to thank The Deanship of Scientific Research at KFUPM for supporting this work under project #IN141009.

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New photodiodes based graphene-organic semiconductor hybrid materials

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental details

Results and discussion

Conclusions

Acknowledgment

Sol. Energy Mater. Sol. Cells

Prog. Polym. Sci.

Sol. Energy

Synth. Met.

Curr. Appl. Phys.

Sens. Actuators B

Synth. Met.

Sol. Energy

Mater. Chem. Phys.

Sol. Energy Mater. Sol. Cells

Phys. B

Sol. Energy

Synth. Met.

Thin Solid Films

Phys. E

Sol. Energy Mater. Sol. Cells

Superlattices Microstruct.