I think I have located the source of your photo, which is an old postcard (postmarked June 17, 1924 in Charlottenburg, and published by Art Studio Schroter, Potsdam). If this is correct, the letters on the radiator are TP, or possibly TIP.
I can't seem to connect this to any known production vehicle, but I have a theory which I can neither prove or disprove, so I will put it in the form of a question, in the hope that it might trigger some ideas which might direct you to something in your research material which I am sure is far greater than mine, especially as it is in your home country. My thought is: Might this vehicle be the result of an academic research project at a local school/university? Somehow the overall appearance of the vehicle (the line, finish, etc.) reminds me of an advanced technical school project, and the date is correct for the period when there was lots of development for this type of light car. I was theorizing something like the Technical Institute Potsdam, or something similar. I don't know if such a place exists, or ever existed, but perhaps you know, or know how to find out.