Studies of Charge Transport Properties in P3HT/ZnO Composites Using Photoinduced Charge Extraction by Linearly Increasin
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Studies of Charge Transport Properties in P3HT/ZnO Composites Using Photoinduced Charge Extraction by Linearly Increasing Voltage Technique Vijila Chellappan1, Furong Zhu1, Minghui Liu2, and Kian Ping Loh2 1 Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research, 3 Research Link, Singapore, 117602, Singapore 2 Department of Chemistry, National University of Singapore, Singapore, 119077, Singapore ABSTRACT The charge transport properties in a mixture of regio-regular (poly 3-hexylthiophene) (RR-P3HT) and Zinc Oxide nano particle (ZnO) have been studied using the photoinduced charge extraction by linearly increasing voltage (PhotoCELIV) technique. We have studied the effect of ZnO nanoparticle size (12 nm and 50 nm) on the charge transport properties by fixing the composition ratio of P3HT/ZnO hybrid. The PhotoCELIV mobility in P3HT/50nm-ZnO at room temperature is found to be 7.8×10-5cm2/Vs at an applied electric field of 2.5 ×104 V/cm, which increases to 1.7×10-4cm2/Vs for P3HT/12nm-ZnO composite. The temperature and electric field dependence of charge mobility in these composites have been studied and analysed using Gaussian disorder formalism. The obtained results suggest that the charge transport properties in P3HT/ZnO composite, at low ZnO concentrations, can be tuned by varying the size of the nanoparticle. INTRODUCTION Conjugated polymers, inorganic nanoparticles, and their composites have attracted significant research interest for the development of optoelectronic devices, such as light emitting diodes, photovoltaics, detectors and optical information memories [1-4]. In particular, the combination of p-type conjugated polymer and n-type nanoparticle is advantageous due to the solution processability of polymers and the high electron mobility of inorganic semiconductors. In recent years, various combinations of p-type conjugated polymers, such as MDMO-PPV (poly[2-methoxy-5-(3 ,7 -dimethyloctyloxy)-1,4-phenylene vinylene]), and regio-regular poly 3hexylthiophene (P3HT), and n-type nanoparticles, such as PbSe, PbS CdS, CdSe, and ZnO have been utilised for the fabrication of bulk hetero junction photovoltaic devices [5-8]. In particular, Zinc Oxide nano crystal particles (nc-ZnO) are attractive because of their less toxicity and inexpensive fabrication process. It has been reported that the solar cells with nc-ZnO/ MDMOPPV composites show the efficiency of 1.6% [9]. It is well known that the performance of the photovoltaic (PV) devices depends on the efficiency of photo charge generation and their charge transport towards the electrodes. Therefore, the PV device performance can be improved through the understanding of charge transport in the composite films. Although significant research effort is focussed on optimising the performance of PV devices, there are only few reports on the charge transport studies in conjugated polymer/nanocrystal composites. Recently, Koster etal [9] have studied the charge transport properties in PPV/ZnO composites using spa
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