This study identified and analyzed the innovation value stages of research fronts and follow-up studies using ESI Research Fronts' core papers, citing papers and core authors' follow-up research papers, including the steps of the indexing of innovation value stage, the proposal of indexes of innovation value stage, the judgment of innovation value stage, the analysis of innovation value stage, the analysis of the stage of innovation value of the research groups, and the identification of the themes of innovation value stages.

The innovation value stage indexing theme and words are determined by literature research and expert consultation. The innovation value stage is indexed from the three structural fields of title, abstract and keyword. The indexing method adopts automatic word-indexing. The innovation value stage indexes are proposed, which the scores are scored according to the position of the indexing words (keyword 4 points, title 2 points, summary 1 point), and the scores of each value stage of each paper are calculated separately, finally, the value stage which has the maximum value is taken as the value stage of the paper. The themes of innovation value stages are identificated by following steps: extracting sentences where the indexed words are located in the abstract, natural language processing, phrase cleaning, expert interpretation.

And the corresponding empirical research is carried out with the research front of "CH3NH3PbI3 perovskite solar cells and inorganic hole transport materials".Finally, the effectiveness of the research method system and the reliability of the empirical results were verified by expert consultation.