Indolinone-substituted methanofullerene—A new acceptor for organic solar cells

Indolinone-substituted methanofullerene, 1-(3,5-di-tret-butyl-4-hydroxybenzyl)-3-(3-cyclopropane[1,9](C60-Ih)[5,6]fullerene-3-yl)-indolin-2-one (HBIM), has been studied as an electron acceptor for polymer–fullerene solar cells. HBIM is easier to synthesize and purify than the standard fullerene derivative for polymer solar cells, PCBM. Optical absorption, solubility, and electrochemical properties of HBIM are reported. Solar cells with the device configuration ITO/PEDOT:PSS/P3HT:HBIM/CaAl have been investigated with the reference cells based on the P3HT:PCBM blend. We study the effect of thermal annealing on the device performance and the surface morphology of the active layer. The power conversion efficiency of P3HT:HBIM devices with a weight ratio of 1:1 is about 2% under illumination by AM1.5G (100 mW/cm2) radiation. The P3HT:HBIM devices show the same open-circuit voltage as the P3HT:PCBM ones, but the short-circuit current and the fill factor are considerably less.