Functionalization of fullerene by polyethylene glycol toward promoted electron transport in inverted polymer solar cells

Abstract

Abstract A novel polyethylene glycol-functionalized fullerene derivative (C60-PEGA) was synthesized by a facile one-step nucleophilic addition reaction. C60-PEGA possessed good solubility in methanol and was estimated as C60-(C8H18N)13H13O with average PEG moiety of 13 by 1H NMR, FT-IR and X-ray photoelectron spectroscopy (XPS). C60-PEGA was applied as an ETL to construct inverted bulk heterojunction polymer solar cells (inverted BHJ-PSCs) based on photoactive layers of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3, 4-b]thiophene-2-carboxylate]: [6,6]-phenyl-C71-butyric acid methyl ester (PTB7-Th: PC71BM), which achieve the best PCE of 9.25%, surpassing that of reference device based on the ZnO ETL (8.61%). The higher ETL performance of C60-PEGA ETL in BHJ-iPSC device relative to that of the ZnO ETL was attributed to the increase of electron mobility and effective electron transport from the active layer to the ITO cathode because that the reduced work function (WF) of ITO via the modification of C60-PEGA leads to the increase of short-circuit current density (Jsc) and consequent PCE.