Highly Efficient Inverted Polymer Solar Cells Based on an Alcohol Soluble Fullerene Derivative Interfacial Modification Material

A phosphate group-containing bisadducts fullerene derivative bis-[6,6]-phenyl-C-60-pentyl phosphoric diethyl ester (B-PCPO) has been developed as an indium tin oxide (ITO) interlayer material in inverted polymer solar cells. The B-PCPO possessed good alcohol solubility, n-type nature, good electron transporting ability, and ITO modification function simultaneously, and it was utilized as an ITO interlayer in solution-processed multilayer inverted bulk-heterojunction polymer solar cells to improve the electron transporting and collection. It was found that the B-PCPO interlayer could effectively decrease the work function of ITO and thereby enhance the electron collection of ITO electrode. The device studies showed that the resulting solar cells' efficiencies were significantly increased from 4.83% to 6.20% by using a B-PCPO interlayer, benefiting from the dramatic enhancement in open circuit voltage and moderate increase in fill factor. Our results provide a promising approach to improve the performance of inverted polymer solar cells.