In many countries, the normal route to a ph.D. involves writing a thesis separately from papers you publish. https://www.hochschulkompass.de/en/doctoral-studie

In many countries, the normal route to a ph.D. involves writing a thesis separately from papers you publish. https://www.hochschulkompass.de/en/doctoral-studies/doctoral-phase/dissertation-research-phase.html https://www.hochschulkompass.de/en/doctoral-studies/doctoral...: The dissertation is the core of your doctoral degree and the most important piece of work you will produce for this degree. It is usually written as a monograph which is a comprehensive, self-contained treatment of a research topic. […] Alongside the monographic dissertation, more and more faculties are offering the possibility of submitting a publication-based dissertation, known as a cumulative dissertation. This consists of several shorter pieces of work which are thematically linked. The totality of the written doctoral works must satisfy the requirements of a monographic dissertation. Faculties which allow cumulative dissertations may have very different requirements, for example in relation to: • The type of publication (book, journals, manuscript) • The current status of the publications (published, submitted, in preparation) • The scope of the publications and the results they contain, etc. If you wish to write a cumulative dissertation, you should find out at an early stage whether this option is available at your faculty and if so, what requirements apply. Even if his university allows such a bundling of papers chances are he still would have to write the texts that describe how they’re linked thematically, and possibly a layman’s description of the work, etc.