Style Question: Use of "we" vs. "I" vs. passive voice in a dissertation

You should probably consult a faculty member, or look at papers in your own field, in order to decide anything definitively. These kinds of conventions can vary within fields and subfields, so you should see what your peers do.

In my field, using I in a paper is something to be avoided whenever possible, by using the passive voice, the pronoun one, or by restructuring the sentence so that the author doesn't need to be referenced. We is more common than I, although it is normally restricted to papers with more than one author.

You are right that German generally favors passive voice much more than in English. However, the main place where I have found that passive voice is more accepted in English is in formal academic writing.