TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The phosphorus-silicate glass layer and the underlying silicon layer are etched in single process step. The contact windows are etched in the back surface multi-layer (passivation layer and silicon nitride) of the wafer using an acidic etching paste, which has selectivity to silicon layers. The method further comprises (a) texturing (1) the surface, (ii) phosphorus doping (65 Omega /sq diffusion of phosphorus oxychloride (2)), (iii) etching the back surface by means of the alkaline etching paste so that the surface is polished and simultaneously the p-n-junction is separated, where the etching paste is printed with stencil printing on the back surface for activating the paste in the belt furnace at 150 degrees C for 5 minutes and rinsing wafer with deionized water, (iv) coating the back surface with silicon dioxide or alumina passivation layer with thickness of 15-30 nm and coating the back and front surface with silicon nitride (70-100 nm) using plasma enhanced chemical vapor deposition (PECVD- silicon nitride), (v) printing the etching paste with screen printing, heating in belt furnace and rinsing with deionized water, and (vi) screen printing for metallization of the surface (front side) and the back surface by sintering (co-firing). Preferred Components: The potassium hydroxide containing etching paste comprises a solvent comprising glycerol, ethylene glycol, polyethylene glycol, octanol, 1,3-propanediol, 1,4-butanediol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dimethylsulfoxide and/or gamma -butyrolactone, 0.1-35 wt.% non-particulate thickener comprising polyvinylpyrrolidone, polyacrylate, carboxymethylcellulose and/or hydroxypropylcellulose, and 0.1-35 wt.% particulate thickener comprising carbon black, fumed silica, magnesium aluminum silicates or low melting wax particles in pure form or in a mixture. EXAMPLE - 70 g Potassium hydroxide, 50g sodium hydroxide and 0.5 g polyvinylpyrrolidone were added to a solvent mixture comprised of 240 g glycerol and 64 g water with vigorous stirring. The clear homogeneous mixture was mixed with 22 g carbon black and stirred for 2 hours to obtain a paste. The paste was printed with a steel template.