A Linear Relation behind Outstanding Crystalline Silicon Solar Cells

In a long history of photovoltaic innovations, various architectures of crystalline silicon solar cells have been evolved to result in the highest conversion efficiency (η) of those days as described in Best Research Cell Efficiency by NREL. The cells are characterized by three parameters of the power max (Pmax), the saturation current (Jsc) and open-circuit voltage (Voc), but the fill-factor (FF) can be deduced from those three parameters. The 36 outstanding cells of those days are picked up from the published papers to be plotted on the η-FF and η-Jsc·Voc planes, in which all kinds of the architectures of the cells are included, for instance, PERC, PERL, PERT, HIT, IBC, TopCon, POLO, POLO-IBC, and Hetero-IBC(HJ-IBC). The plots of the η of those outstanding solar cells against their FF or Jsc·Voc clearly reveal a linear relation among them, even they have been independently evolved. The linear relation seems to have some effective meanings. The linear relation being assumable as a straight line, a 87% of FF on the line, which was predicted as the limit of FF by M. Reusch, can meet well with 29% to 30% in efficiency, which have been expected as the efficiency limit of crystalline silicon solar cells by W. Schockley and J. Queisser, and R. Swanson.