Method for raw etching silicon solar cells

Abstract

The present invention relates to a novel process for producing textured surfaces on multicrystalline, tricrystalline and monocrystalline silicon surfaces of solar cells or on silicon substrates which are used for photovoltaic purposes. It relates in particular to an etching process and an etching agent for producing a textured surface on a silicon substrate.

1 . Etching mixture for producing a textured surface on multicrystalline, tricrystalline and monocrystalline silicon surfaces of solar cells or on silicon substrates, for photovoltaic purposes, comprising hydrofluoric acid and mineral acids selected from the group consisting of nitric acid, sulphuric acid and phosphoric acid.  
     
     
         2 . Etching mixture according to  claim 1 , comprising hydrofluoric acid, nitric acid and sulphuric acid and/or phosphoric acid.  
     
     
         3 . Etching mixture according to claims  1 - 2 , characterized by an additional oxidizing agent which suppresses the formation of nitrogen oxides and, if appropriate, a surface-active substance selected from the group consisting of the polyfluorinated amines and the sulphonic acids.  
     
     
         4 . Etching mixture according to claims  1 - 3 , characterized by an additional oxidizing agent selected from the group consisting of hydrogen peroxide, ammonium peroxydisulphate and perchloric acid.  
     
     
         5 . Etching mixture according to claims  1 - 4 , comprising 1-30% HF, 5-30% nitric acid, 50 to 94% concentrated sulphuric acid or concentrated phosphoric acid or 50 to 94% of a mixture of concentrated sulphuric acid and concentrated phosphoric acid.  
     
     
         6 . Process for producing textured surfaces on multicrystalline, tricrystalline and monocrystalline silicon surfaces of solar cells or on silicon substrates for photovoltaic purposes, in which 
 a) an etching mixture according to  claims 1  to  5  is brought into contact with the entire surface at a suitable temperature by spraying, dipping, capillary coating or meniscus coating, resulting in incipient isotropic etching, and    b) the etching mixture is rinsed off after a sufficient duration of action.    
     
     
         7 . Process according to  claim 6 , characterized in that in addition to the texture etching damage etching takes place, in which an etching mixture which comprises 10-16% HF, 20-30% HNO 3 , 15-25% H 2 SO 4 , 14-20% H 3 PO 4  and 20-30% water is used.  
     
     
         8 . Process according to  claims 6  to  7 , characterized in that the etching operation is carried out at a temperature of between 15 and 30° C., in particular at room temperature.  
     
     
         9 . Process according to  claims 6  to  8 , characterized in that a duration of action of between 2 and 30 minutes is selected.  
     
     
         10 . Process according to  claim 6 , characterized in that an etching mixture which comprises 3-7% HF, 3-7% HNO 3 , 75-85% H 2 SO 4  and 5-15% water is used for the rough-etching and is rinsed off after a duration of action of 1-5 minutes.