The present invention provides a process for preparing a solution of electrically uncharged [(OH)x(NH3)yZn]z where x, y and z are each independently 0.01 to 10, comprising at least the steps of (A) contacting ZnO and/or Zn(OH)2 with ammonia in at least one solvent in order to obtain a solution of electrically uncharged [(OH)x(NH3)yZn]z where x, y and z each independently 0.01 to 10 with a concentration c1, (B) removing some solvent from the solution from step (A) in order to obtain a suspension comprising Zn(OH)2, (C) removing solid Zn(OH)2 from the suspension from step (B), and (D) contacting the Zn(OH)2 from step (C) with ammonia in at least one solvent in order to obtain a solution of electrically uncharged [(OH)x(NH3)yZn]z where x, y and z are each independently 0.01 to 10 with the concentration c2, and to highly concentrated solutions of electrically uncharged [(OH)x(NH3)yZn]z where x, y and z are each independently 0.01 to 10, to a process for producing a layer comprising at least zinc oxide on a substrate, comprising at least the steps of (E) preparing a solution of electrically uncharged [(OH)x(NH3)yZn]z where x, y and z are each independently 0.01 to 10 by the former process according to the invention, (F) applying the solution from step (E) to the substrate and (G) thermally treating the substrate from step (F) at a temperature of 20 to 450° C. in order to convert electrically uncharged [(OH)x(NH3)yZn]z where x, y and z are each independently 0.01 to 10 to zinc oxide.