Identifying technological sub-trajectories in patent data: the case of photovoltaics

This paper proposes a patent search strategy for photovoltaics which allows distinguishing patents of the photovoltaic system into sub-trajectories. Identifying and analyzing sub-trajectories is of particular importance for understanding micro patterns of technological change. The proposed search strategy is modular and replicable. It performs similar to benchmark search strategies and allows us to distinguish three cell sub-trajectories and two system components. The identified sub-trajectories allow a more detailed economic analysis previously not possible. Descriptive analyses reveal that inventive activity differs between sub-trajectories and countries. The market dominating silicon wafer cell sub-trajectory shows hardly any patented inventive activity even though it dominates the market. Furthermore, there are shifts in relative patenting activity between sub-trajectories, previously unnoticed at the trajectory level. Country comparison reveals that Asian countries focus on the emerging cell sub-trajectory, fostering their competitive advantage. The USA focuses on the established thin-film sub-trajectory, and inventive activity in Germany focuses on module components. The results have several implications for policy, for example, questioning the effectiveness of demand pull policies for inventive activity, and economic theory. The empirical assessment of sub-trajectories can increase understanding of technological change and uncover dynamics not observable at the trajectory level.