Correlation between R&D expenditures and conversion efficiency improvement in R&D on solar cells

The objective of this paper is to show the main motive force of technological progress on solar cells by analyzing correlation between R&D expenditures and conversion efficiency improvement. In the analysis, instead of R&D expenditures, expected conversion efficiency improvement, which is defined as product of cost efficiency from the viewpoint of conversion efficiency improvement and actual R&D expenditures, is used. Based on results of the analysis, expected and actual conversion efficiency improvement show good correlation. This means R&D expenditures are the main motive force of technological progress on solar cells and they are appropriate variables for modeling technological progress of solar cells.