Benefit of textured CIGS cells for low reflecting nanogrid application
- PDF / 725,968 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 71 Downloads / 157 Views
Benefit of textured CIGS cells for low reflecting nanogrid application Joop van Deelen1, Y. Tezsevin, A. Omar1, M. Xu2, M. Barink3 1 Solliance/TNO, High Tech Campus, 21, 5656 AE, Eindhoven, The Netherlands. 2 TNO, Stieltjesweg 1, Delft, The Netherlands. 3 Holst Centre/TNO, High Tech Campus 31, 5656 AE, Eindhoven, The Netherlands ABSTRACT We show the results of nanotextured device designs combined with carefully placed nanogrids in order to minimize optical losses. Finite element method (FEM) based optical modeling indicates that the reflection of both the layer stack and the metal is diminished by the proposed configuration in which the metallic nanowires at the front of a device are placed into the relatively shallow crevices, whereby the metal is not covered by other materials of the cell stack. The electric field distribution and energy dissipation (i.e. absorption) diagrams of the texture show how the light is distributed and where it is absorbed. It shows that light is ‘concentrated’ in the tips of the texture (depending on the size and wavelength of the light). Simultaneously, for wavelengths above 750 nm there appears to be a reduction of the E-field in the lower part of the texture and, therefore, putting a metallic nanowire in this position has hardly any negative optical effect. Furthermore, the impact of the texture height up to 1000 nm and the nanowire width up to 150nm was systematically investigated for a texture and wire period of 500 nm. The spectra reveal dimension dependent and wavelength specific optical features. This is the case even if the flat nanowire remains fully exposed to the front glass medium (i.e. not embedded underneath absorbers). At a texture height of 900 nm, the reflection related current loss is reduced by an order of magnitude compared to flat layer stacks, virtually regardless of the width of the metal nanowire. This opens up exciting new ways of creating nano-metal containing devices without the usual optical losses. INTRODUCTION Transparent conductors are vital for many optoelectronic devices and thin film solar cells in particular. Recently, the combination of metallic grids and transparent conductive oxides (TCOs) was shown to be a good candidate to give front contacts a low resistance without compromising the high transmittance too much [1-5] and its potential benefit for Cu(In,Ga)Se2 (CIGS) cells was calculated [6]. Downsizing metallic grids to the nano domain might reduce the optical loss [7,8]. However, the transparency of these metal nanostructures is often below 80%, depending on the metallic feature size [9,10]. Moreover, cloaking of metals in metamaterials has been reported [11-13]. Narasimhan et al. demonstrated the application of this concept by making a hybrid metal-silicon nanostructure: a 16 nm thick gold mesh pattern with 65% surface coverage was deposited on a Si wafer, which was followed by a gold catalyzed etching step and the gold nanomesh ended up at the bottom of the etched silicon crevice [14]. With this procedure a decrease of the initial reflection fr
Data Loading...
