Titania-German Nanocomposites for Quantum Dot Solar Cells
- PDF / 3,136,987 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 33 Downloads / 195 Views
0974-CC05-06
Titania-German Nanocomposites for Quantum Dot Solar Cells Amita Goyal1, Sukti Hazra2, and S. Ismat Shah3,4 1 Physics and Astronomy, University of Delaware, Sharp Lab, Newark, DE, 19716 2 Center for Composite Materials, University of Delaware, Newark, DE, 19716 3 Materials Sceince and Engineering, University of Delaware, 201 Dupont Hall, Newark, DE, 19716 4 Physics and Astronomy, University of Delaware, 214 Sharp Lab, Newark, DE, 19716
ABSTRACT Several new photovoltaic semiconductor materials and technologies have been developed due to the increasing need for renewable energy sources. Quantum dot (QD) based solar cell is potentially one of the best contenders. We have developed a thermodynamically stable nanocomposite (stable up to 900°C) titania-germanium (TiO2-Ge) which shows promise as the active layer for QD solar cells. In TiO2-Ge nanocomposites Ge nanodots are distributed in a TiO2 matrix. Due to the 3-D quantum confinement effect, tailoring of the optoelectronic properties is relatively easily done by simply varying the Ge nanodots size. Ge is particularly advantageous since its Bohr radius is relatively large, 25 nm. In this paper results of the variation of the optoelectronic properties of TiO2-Ge nanocomposites as a function of the nanostructure parameters are presented. TiO2-Ge nanocomposite thin films were synthesized using RF magnetron sputtering. The structural studies (by XRD, HRTEM) established the fact that the Ge concentration in the composite target governs the size of the Ge nanodots whereas RF sputtering power controls the density of Ge nanodots in the nanocomposite films. The optical spectroscopic studies showed that the variation of the size of Ge nanodots in the TiO2-Ge films shifts the absorption edge from ~ 0.66 eV (infrared) to ~ 2.3 eV (blue-green). Similarly, dark conductivity also varies in a wide range of 10-7- 10-2 Scm-1 by altering the concentration as well as the structural phase (amorphous or crystalline) of Ge. INTRODUCTION Over the years, research has offered solar cells ranging from silicon solar cells [1] (based on p-n junction), thin film cells like CdSe, CdTe, CdS, GaAs, InP [2], and organic solar cells like dye sensitized solar cells (DSCs) [3] to tandem cells [4]. However, the problems of high cost, and low efficiencies have restricted the popularity of this form of energy conversion. By far the highest achievable efficiency is 39% obtained by tandem cells [4]. On the other hand Graetzel cells, based on the principal of dye sensitization of TiO2 nanoparticles with an organic dye, offer a low cost solar device based on nanostructured TiO2. TiO2 is a promising semiconductor for photovoltaic applications due to its stability, inertness, cost, etc. Optical band gap of TiO2 is 3.2 eV that lies in the ultraviolet region. The peak of solar spectrum, however, is in the visible region. Therefore, to increase the quantum efficiency of the photovoltaic devices based on TiO2 nanoparticles, these nanoparticles are generally sensitized by various methods. So far dye sensiti
