Effect of Crystallinity of Fullerene Derivatives on Doping Density in the Organic Bulk Heterojunction Layer in Polymer Solar Cells

Polymer solar cells（PSCs） based on poly（3-hexylthiophene）(P3HT) and[6,6]-phenyl-C61-hutyric acid methyl ester（PCBM） are fabricated by using 1,8-diiodooctane（DIO） as a solvent additive to control the doping density of the PSCs.It is shown that the processing of DIO does not change the doping density of the P3 HT phase,while it causes a dramatic reduction of the doping density of the PCBM phase,which decreases the doping density of the whole blend layer from 3.7×10;cm;to 1.2 × 10;cm;.The reduction of the doping density in the PCBM phase originates from the increasing crystalhnity of PCBM with DIO addition,and it leads to a decreasing doping density in the blend film and improves the short circuit current of the PSCs.