| AVS 58th Annual International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Thursday Sessions |
| Session EN-ThP |
| Session: | Energy Frontiers Poster Session |
| Presenter: | José A. Diniz, State University of Campinas, Brazil |
| Authors: | A.R. Silva, State University of Campinas, Brazil J. Miyoshi, State University of Campinas, Brazil F.A. Cavarsan, State University of Campinas, Brazil L.P.B. Lima, State University of Campinas, Brazil J.A. Diniz, State University of Campinas, Brazil |
| Correspondent: | Click to Email |
The solar cell efficiency is hardly connected with device fabrication processes, such as texturing silicon surface, which increases the surface absorption area of incident radiation on the cell and, consequently, reduces the substrate reflectance. Nowadays, solar cells based on silicon substrate are fabricated with texturing surfaces to increase the device efficiency. These surfaces are obtained by anisotropic wet etching in KOH and NaOH alkaline solutions [1]. The disadvantage of these solutions are K+ and Na+ ions from KOH and NaOH, which are mobile charges in Metal-Oxide-Silicon structures. Thus, these solutions are not compatible for CMOS technology, which is used for integration circuits and devices on silicon surface. As an advantage, using these alkaline solutions, the <111> planes of silicon substrate with (100) crystallographic orientation are exposed, resulting in groups of pyramid on silicon surface. The pyramids induce many reflections and scatterings of the incident radiation, which increase the light absorption on the surface. This effect is defined as light trapping [1]. In this work, the silicon substrate texturing is carried out by an anisotropic wet etching, with an alkaline solution based on NH4OH,because this solution can form pyramids on the surface, does not release alkaline products/reagents on the silicon surface and is fully compatible with the CMOS technology. With this solution (concentration of 9%wt of NH4OH and four magnetic stirring velocities) the <111> planes of silicon substrate with (100) crystallographic orientation are exposed and theses planes can form some pyramids on surface. Scanning Electron Microscopy analysis presents that these pyramids are observed all long on the surface, indicating that the wet etching was uniform on the substrate. Furthermore, the pyramid height values are between 3.5 and 7.2 µm, and the silicon etching wet rate was about of 0.7 µm/minute. The reflectance measurements show that the surfaces with and without texturing present reflectance values of about 16% and 38%, respectively. The reflectance values of about 16% with texturing are similar to the results from references [1], which have used KOH solution. This result indicated that our texturing process based on NH4OH, which is fully compatible with the CMOS technology, can be used to fabricate Si-based solar cells [2].
REFERENCES
[1]L.A. Dobrzański, A.Drygała, Surface texturing of multicrystalline silicon solar cells, JAMME,Volume 31 ISSUE1,November 2008.
[2J J.Lu, W.Liu, C.H.M. van der Werf,A.Y.Kovalgin,Y. Sun, R. E. I. Schropp and J.Schmitz, Above-CMOS a-Si and CIGS Solar Cells for Powering Autonomous Microsystems, IEDM, December 2010