Figure 7: Calculated singlet yield for F8-PFB devices measured as a function of temperature. The two dashed red vertical lines give the upper and lower limits on our best determinations of the ISC yield of this polymer. Clearly, it is seen that the singlet yield depend strongly on temperature. At room temperature, the yield is ca. 0.33, still appreciably above the 0.25 limit of spin-independent recombination.