NOVELTY - Preparing silicon dioxide-dispersion containing phosphoric acid, comprises adding phosphoric acid to a starting dispersion (I) containing water and silicon dioxide-particle under stirring to obtain a starting dispersion (II), and subsequently adding at least a silicon compound to (II) and hydrolyzing the silicon compound, where the starting dispersion (II) contains water, silicon dioxide and phosphoric acid.    USE - The silicon dioxide-dispersion is useful for coating a substrate, preferably silicon-wafer, which is useful for the manufacture of solar cells (all claimed).    ADVANTAGE - The process provides safe installations to avoid the damage of the coated wafers.    DETAILED DESCRIPTION - Preparing silicon dioxide-dispersion containing phosphoric acid, comprises adding phosphoric acid to a starting dispersion (I) containing water (80-95 wt.%) and silicon dioxide-particle under stirring to obtain a starting dispersion (II), and subsequently adding at least a silicon compound to (II) and hydrolyzing the silicon compound, where: the starting dispersion (I) contains water and silicon dioxide (5-20 wt.%); the sum of water and silicon dioxide is at least 98 wt.%; (II) contains water (60-90 wt.%), silicon dioxide (5-20 wt.%) and phosphoric acid (5-25 wt.%), which is orthophosphoric acid, diphosphoric acid and/or polyphosphoric acid; the sum of water, silicon dioxide and phosphoric acid is at least 98 wt.%; the silicon dioxide particle of the starting dispersion (I) and (II) exhibits a Brunauer, Emmett and Teller (BET) surface of 80-350 m2/g and an average aggregate diameter of less than 200 nm, and the silicon compound is of formula ((R1O)xSi(OR2)4-x); and the ratio of silicon dioxide from hydrolysis (calculated)/silicon dioxide from the starting dispersion (II) is 0.2-1.2.    R1, R2 = methyl, ethyl, n-propyl, iso-propyl or n-butyl; and    x = 0-4.    Where R1 is not equal to R2. INDEPENDENT CLAIMS are included for:    (1) a silicon dioxide-dispersion containing phosphoric acid, obtained by the above process; and    (2) coating a substrate, comprising applying the silicon dioxide-dispersion containing phosphoric acid on a substrate, subsequently drying the coated substrate and sintering.