Solar Energy Materials & Solar Cells 91 (2007) 1943–1947 Optimization of sodium carbonate texturization on large-area crystalline silicon solar cells N. Marrero a , B. Gonza´lez-Dı´az a , R. Guerrero-Lemus a,Ã , D. Borchert b , C. Herna´ndez-Rodrı´guez a a Departamento de Fı´sica Ba´sica, Universidad de La Laguna, Avda, Astrofı´sico Francisco Sa´nchez, 38204 La Laguna, S/C de Tenerife, Spain b Auf der Reihe 2, Institut fu ¨r Solare Energiesysteme, Fraunhofer Institut, 45884 Gelsenkirchen, Germany Received 19 April 2007; accepted 6 August 2007 Available online 18 September 2007 Abstract This work describes a texturization method for monocrystalline silicon solar cells based on a mixture of sodium carbonate and sodium hydrogen carbonate solutions. A specific solution has been found that results in an optimal etching rate, the lowest surface reflectance and a homogeneous density of pyramidal structures on the silicon surface. The subsequent phosphorus diffusion with rapid thermal processes has been modified in order to drastically reduce the process time and, simultaneously, to obtain a high homogeneity of the sheet resistance values and improved photocarriers lifetimes. 100 Â 100 mm solar cells with an efficiency of 15.8% have been obtained compared to an efficiency of 14.7% for the reference cell. r 2007 Elsevier B.V. All rights reserved. Keywords: Alkaline texturization; Texturisation; Rapid thermal processing; c-Si 1. Introduction To obtain high efficiency in a silicon-based solar cell, the substrates must be submitted to multiple and costly steps [1]. One of these steps is a saw damage etching of the substrate [2], and it is carried out by immersion of the substrate in a chemical solution. Also, an antireflection coating is normally formed in the front side of the substrate to avoid optical losses and to improve the photoconversion effect, usually by means of a silicon nitride (SiN x ) deposition [1]. The texturization method can produce simultaneously the saw damage etching by removing the outermost silicon layers of the samples where a high density of defects is situated, and can promote antireflec- tion properties by forming pyramidal structures on the silicon surface [3]. Commonly, the etching solutions are a mixture of potassium hydroxide (KOH) or sodium hydroxide (NaOH) with a high concentration of isopropyl alcohol (IPA) [3–6]. As IPA is an expensive chemical product, other solvents are studied to reduce the cost of the process [7]. Alternative solvents are sodium carbonate (Na 2 CO 3 ) [8,9], potassium carbonate (K 2 CO 3 ) [10] and sodium phosphate (Na 3 PO 4 ) [11,12]. Particularly, Na 2 CO 3 is a compound that (i) has provided satisfactory reflection values when it is used in the texturization of small-area silicon wafers [12], (ii) is commonly used in the glass industry [13], (iii) has a lower cost than the other referred compounds [14], and (iv) is not as unhealthy to manipulate as the other compounds referred [15]. Thus, Na 2 CO 3 seems to be the best etchant to be transferred to a large-scale production of crystalline silicon solar cells [8]. After obtaining substrates with low reflectance, nor- mally, the next step in the production of silicon solar cells is the formation of phosphorus emitters. Rapid thermal processing (RTP) is an interesting option for the formation of the emitter in the photovoltaic industry [16]. The advantages of RTP compared to the conventional furnace processing (CFP) are well known: (i) RTP drastically ARTICLE IN PRESS www.elsevier.com/locate/solmat 0927-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2007.08.001 Ã Corresponding author. Tel.: +34 922 318306; fax: +34 922 318228. E-mail address: rglemus@ull.es (R. Guerrero-Lemus).