Electrospun photonics topography for organic photovoltaics

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Electrospun photonics topography for organic photovoltaics Khadija Kanwal Khanum1, and Praveen C. Ramamurthy1,2* 1

Department of Materials Engineering, Indian Institute of Science, Bangalore, India

2

Center for Nanoscience and Engineering, Indian Institute of Science, Bangalore, India

*[email protected]

ABSTRACT A Photonics device requires uniform periodic structural arrangement. Various techniques have been used to fabricate these types of structures, which employs several steps of fabrication. This work proposes single step hierarchical array of equal submicron size porous structure fabricated through tuning electrospinning processing parameters. The dictating parameters were high voltage, tip to collector distance and solvent used on the evolving structure. Morphological and optical investigations suggested the uniform periodic topography and enhancement in light absorption, which is assumed due to internal reflection of light. This structure was evaluated for better light harvesting as active layer in organic photovoltaic devices using poly (3 hexyl thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend, and further studying enhancement in photoelectrical characteristics.

INTRODUCTION Photonic structure benefits in harvesting of light by internal reflection. Main criteria for a photonic structure are getting a uniform periodic pattern. Several fabrication methods have been reported like template synthesis, self assembly. Here fabrication of single step hierarchical structure using electrospinning techniques is evaluated. Electrospinning is attractive technique to generate fibers in sub micron range [1]. In this process polymer solution is drawn through the nozzle by applying high voltage between nozzle tip and collector. It has gain popularity due to the possibility of having wide control over fiber diameter and morphology, by studying and finetuning various process parameters like applied voltage, flow rate, tip to collector distance, deposition time, viscosity [2] and solvent utilized [3]. Here in this study poly (3 hexyl thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) [4], was electrospun at wide range of voltage and distance to obtain photonic structures. Devices were fabricated of these structures as active layers to study its photoelectrical responses.

EXPERIMENTAL DETAILS

Regioregular P3HT was purchased from Rieke metals, Inc. PCBM from Nano-C, chloroform, analytical grade from S D fine chem. Ltd. Solution containing P3HT:PCBM in ratio of 1:0.8 was stirred for overnight. Electrospinning set-up consisting of high voltage source (Gamma RR50) and syringe pump (Holmarc SPL-2D) was used to perform the optimization and fabrication. Applied voltage was varied from 5-8kV, flow rate and tip to collector distance were kept constant at 7cm and 50 µl/min respectively. Spincoating for comparison device was done at 1000 rpm for 60sec. Morphological studies were performed using FESEM (Field emission scanning electron microscope Ultra 55) and AFM (Atomic force microscope B

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