Before you write your introduction, you must know what a research is first. It makes every stage of writing easier. Research is defined as a premeditated investigation using scientific methodology (quantitative, qualitative, experimental, observation and so on) to solve a serious problem (not ordinary problem), thus creating additional (new) knowledge. Research is also regarded as an inquiry of reality about something by testing a hypothesis, answering questions, generating new queries, finding solutions, and creating new knowledge. (Heikkinen, et al, 2016).
The new knowledge must be applicable/defensible and challengeable by other researchers, besides lending itself to generalization. For a piece of exploration to qualify as a research, it must pass through a set of rigorous examinations such as validity (logical procedure to answer a question), reliability (quality of measurement), and unbiased conclusion (adequate measures are taken to make sure that it is free from individual interest). As such, a PhD thesis must meet the above conditions of a scientific research procedure. (Mincu & Monica 2015).