Water/Alcohol Soluble Neutral Fullerene Derivative to Reengineer the Surface of the Electron Extraction Layer for High Efficiency Inverted Polymer Solar Cells

Dipole induced vacuum level shift has been demonstrated to be responsible for the enhanced efficiency in polymer solar cells (PSCs), as the modified energy level alignment could reduce the energy barrier and facilitate charge transport, hence result in enhanced efficiency of PSCs. Herein, we report a new mechanism towards enhanced efficiency by using a water/alcohol-soluble neutral fullerene derivative to reengineer the surface of zinc oxide (ZnO) electron extraction layer (EEL) in PSCs with an inverted device structure. Due to neutral property of fullerene derivatives, a negligible change in open circuit voltage is observed from the inverted PSCs with neutral fullerene derivative layer. The neutral fullerene derivative layer greatly increased the surface electrical conductivity of ZnO EEL, suppressed the surface charge recombination, and increased the short circuit current and fill factor, resulting in more than 30% enhanced efficiency from the inverted PSCs. These results demonstrated that the surface electrical conductivity of EEL plays an important role in high performance inverted PSCs