The PhD thesis can have two different formats: it can be written either as a monograph, or as a collection of at least three papers which have been published (or accepted for publication) as journal articles or book chapters, preceded by an (unpublished) introductory chapter. In the case of a monograph, it is still required that you have at least one article or book chapter published (or accepted for publication). Publications must belong to categories 1.1, 1.2, or 3.1 in the ETIS document “Publication classification”. Until you have the required kind and number of publications, you will not be able to submit your manuscript for defence.
For questions, please contact the PhD Program Manager Francesco Orsi (orsi [ät] ut.ee).