Oligo- and Polythiophene/ZnO Hybrid Nanowire Solar Cells

Abstract

We demonstrate the basic operation of an organic/inorganic hybrid single nanowire solar cell. End-functionalized oligo-and poly-thiophenes were grafted onto ZnO nanowires to produce p-n heterojunction nanowires. The hybrid nanostructures were characterized via absorption and electron microscopy to determine the optoelectronic properties and to probe the morphology at the organic/inorganic interface. Individual nanowire solar cell devices exhibited well-resolved characteristics with efficiencies as high as 0.036%, Jsc= 0.32 mA/cm 2 , Voc= 0.4 V, and a FF= 0.28 under AM 1.5 illumination with 100 mW/cm 2 light intensity. These individual test structures will enable detailed analysis to be carried out in areas that have been difficult to study in bulk heterojunction devices. are an area of immense study as they are alternatives to organic bilayer 3 and bulk heterojunction device structures. 4,5 The organic/inorganic hybrid system [6][7][8][9] has opened new opportunities for the development of future generation solar cells, new device technologies, and a platform to study three-dimensional morphology. 10A multitude of concepts have been demonstrated by combining p-type donor polymers with n-type acceptor inorganic nanostructures such as CdSe, 6,7,11 TiO 2 , [8][9][10][12][13][14][15] and ZnO. [8][9][10]14 One-dimensional (1-D) inorganic semiconductor nanostructures are among some of the most attractive nanomaterials for solar cell devices because they provide a direct path for charge transport. 2Other advantages include high carrier mobilities, solution processability, thermal and ambient stability, and a high electron affinity necessary for charge injection from the complementary organic donor material. ZnO nanowires are an example of this class of materials that have been used for hybrid solar cells. [8][9][10]14,16 Poly(3-hexylthiophene) (P3HT)/ZnO nanowire composite solar cells are benchmark systems that have attained power conversion efficiencies ranging from 0.02 to 2%. 9,16,17 In spite of the vast efforts in this area of research, solar cells based on hybrid composites have yielded efficiencies only close to those of organic bilayer devices and significantly less than organic bulk heterojunction solar cells. Knowledge regarding interfacial charge separation and/or transport in hybrid nanowire devices is only partly understood. 10,17 If this class of materials is to play a part in the future of next generation solar cells, then there must be an improved fundamental understanding of the organic/inorganic interface in order to improve power conversion efficiencies. While nanowire array and bulk inorganic/organic blend devices are technologically relevant, their electrical properties 2 depend on nanostructure size, uniformity, crystallinity, phase segregation, interfacial interactions, mobility, trap density and many other factors. For macroscopic devices, these parameters can vary significantly over the active area, making it difficult to attribute any change in performance to a particular phenomenon. Si...

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…Thus, longer ZnO nanowires allowed the fabrication of thicker active polymer layers, and resulted in higher efficiency [485]. The polymers could be functionalized to give chemical bonds with the ZnO nanowire surface [486]. The band diagram of this hybrid structure is illustrated in Fig.…”

First principles investigations on the electronic structure of anchor groups on ZnO nanowires and surfaces

“…25 However, earlier investigations reported non-uniform coverages or even physisorbed layers of these functional groups. 24 Several chemisorbed [27][28][29][30][31] and physisorbed molecules [32][33][34][35][36][37] on ZnO have been theoretically investigated. The chemical stability of carboxyl (-COOH) groups on ZnO has been confirmed by theoretical tight-binding 27 and first-principles calculations.…”

Semiconductor nanowires for photovoltaic and photoelectrochemical energy conversion

“…For example, in polymer-inorganic hybrid PVs, an improved understanding of the interfacial properties is crucial to increase device efficiencies [26], but can be difficult to analyze in large-scale devices due to localized variations in material properties and interface quality. To address this issue, we fabricated individual NW inorganic-organic hybrid PV devices consisting of a single-crystalline ZnO NW core and an organic shell of end-functionalized oligoand polythiophenes, which were grafted onto the NW surface using solution processing techniques to form a radial p-n junction [27]. Individual NWs were characterized by TEM, showing a core-shell structure, allowing for a visualization of the morphology of the inorganicorganic interface.…”