Self-Assembled, Aligned ZnO Nanorod Buffer Layers for High-Current-Density, Inverted Organic Photovoltaics

Rao, Arun D and Karalatti, Suresh and Thomas, Tiju and Ramamurthy, Praveen C (2014) Self-Assembled, Aligned ZnO Nanorod Buffer Layers for High-Current-Density, Inverted Organic Photovoltaics. In: ACS APPLIED MATERIALS & INTERFACES, 6 (19). pp. 16792-16799.

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Abstract

Two different soft-chemical, self-assembly-based solution approaches are employed to grow zinc oxide (ZnO) nanorods with controlled texture. The methods used involve seeding and growth on a substrate. Nanorods with various aspect ratios (1-5) and diameters (15-65 nm) are grown. Obtaining highly oriented rods is determined by the way the substrate is mounted within the chemical bath. Furthermore, a preheat and centrifugation step is essential for the optimization of the growth solution. In the best samples, we obtain ZnO nanorods that are almost entirely oriented in the (002) direction; this is desirable since electron mobility of ZnO is highest along this crystallographic axis. When used as the buffer layer of inverted organic photovoltaics (I-OPVs), these one-dimensional (1D) nanostructures offer: (a) direct paths for charge transport and (b) high interfacial area for electron collection. The morphological, structural, and optical properties of ZnO nanorods are studied using scanning electron microscopy, X-ray diffraction, and ultraviolet-visible light (UV-vis) absorption spectroscopy. Furthermore, the surface chemical features of ZnO films are studied using X-ray photoelectron spectroscopy and contact angle measurements. Using as-grown ZnO, inverted OPVs are fabricated and characterized. For improving device performance, the ZnO nanorods are subjected to UV-ozone irradiation. UV-ozone treated ZnO nanorods show: (i) improvement in optical transmission, (ii) increased wetting of active organic components, and (iii) increased concentration of Zn-O surface bonds. These observations correlate well with improved device performance. The devices fabricated using these optimized buffer layers have an efficiency of similar to 3.2% and a fill factor of 0.50; this is comparable to the best I-OPVs reported that use a P3HT-PCBM active layer.

Item Type:	Journal Article
Publication:	ACS APPLIED MATERIALS & INTERFACES
Publisher:	AMER CHEMICAL SOC
Additional Information:	Copy right for this article belongs to the AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Keywords:	inverted organic photovoltaics; self-assembly; zinc oxide nanorods; electron collectors
Department/Centre:	Division of Chemical Sciences > Materials Research Centre Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	20 Nov 2014 04:52
Last Modified:	20 Nov 2014 04:52
URI:	http://eprints.iisc.ac.in/id/eprint/50310

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