Preparation and characteristics of hybrid ZnO-polymer solar cells
L. W. Ji•W. S. Shih•T. H. Fang•C. Z. Wu•S. M. Peng •T. H. Meen
Received: 15 October 2009 / Accepted: 18 February 2010 / Published online: 3 March 2010 Ó Springer Science+Business Media, LLC 2010
Abstract We demonstrate a hybrid solar cell which was made by blending nanocrystalline ZnO (nc-ZnO) and conjugated polymer regioregular poly(3-hexylthiophene) (P3HT) as the active layer of the solar cell. It can be seen that the efficiency of this new type of solar cells obviously varied as the size and morphology of ZnO nanostructures. The short-circuit photocurrent, fill factor, and power con-version efficiency were enhanced while the smaller nc-ZnO was utilized in such a device.
Introduction
Organic photovoltaic devices have attracted much interest these days due to their potential for the production of flexible and large-area solar cells at low cost [1]. Polymer or organic solar cells often utilize a nanostructured interpen-etrating network of electron-donor and electron-acceptor materials [2–6]. In other word, so-called hybrid polymer solar cells use a blend of conjugated polymer and inorganic material to convert sunlight into charges [5]. Moreover, it can be expected that such a devices will integrate the advantages of two materials—high electron mobility of inorganic semiconductors and photosensitivity, and high
hole mobility of conjugated polymers [7]. However, cur-rently the power conversion efficiency (PCE, g) of the hybrid polymer photovoltaic devices is still very low due to the poor interfacial junction between the organic and inor-ganic materials. Hence, many investigations on improving the heterojunction between the two materials has been reported [7–10].
Since a conjugated polymer can provide exciton (bound electron–hole pair) rather than free charges by photoexci-tation, it is very critical that the use of two materials with complementary p and n type electronic properties in the operation of a hybrid polymer solar cell. The exciton may be dissociated efficiently at the interface of organic– inorganic materials via a hole or electron transfer to generate the photocurrent. In addition, the exciton in con-jugated polymers has a short lifetime (*sub-nanosecond) and a correspondingly small diffusion range (\10 nm), hence many organic solar cells are designed to have a large area interface at short distances (nanometer) from any-where within two materials by either using a bulk hetero-junction, or via a nanoporous structure in which the two materials are mixed on a nanometer scale. On the other hand, both the p and n type materials should offer continuous interpenetration pathways to transport the photocurrent to the electrodes for an efficient photovoltaic device [11–14]. In this work, we blended nanocrystalline ZnO (nc-ZnO) and regioregular poly(3-hexylthiophene) (P3HT) as an active layer of the hybrid bulk heterojunction solar cells, where two different morphology of nc-ZnO were employed in solution processes. No additional surfactants or ligands were needed to disperse the nc-ZnO in P3HT solvent [5]. Here, inorganic semiconductor ZnO was used as the n-type material in combination with the p-type conjugated poly-mer P3HT. Size effects of the nc-ZnO can be observed by measuring current density–voltage (J–V) under AM 1.5 L. W. Ji W. S. Shih T. H. Fang (&)
C. Z. Wu S. M. Peng T. H. Meen
Graduate Institute of Electro-Optical and Materials Science, National Formosa University, Yunlin 632, Taiwan
e-mail: fang.tehua@msa.hinet.net T. H. Fang
Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan
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J Mater Sci (2010) 45:3266–3269 DOI 10.1007/s10853-010-4336-4
Acknowledgements This work was supported by National Science Council of Taiwan under contract number NSC 95 2221E150077MY3. The authors would like to thank Prof. Y. K. Su and S. J. Chang at the Advanced Optoelectronic Technology Center, National Cheng Kung University, Taiwan, for support through equipment and cooperation.
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