Substituent effect on orbital energy of fulleropyrrolidine derivatives

Abstract

Extensive studies on fullerene derivatives have been made for the application in material science. Recently, we found that one of the series of N-methoxyethoxyethyl-2-(substituted phenyl)fulleropyrrolidine derivatives worked as a good acceptor partner in a P3HT-based thin film solar cell giveing the a high power conversion efficiency. However, the guiding principle for such high efficiency is still unclear. Density functional calculations have been performed for a series of fulleropyrolidine derivatives 1 with various substituents. A considerable positive correlation is found between the orbital energy of LUMO of 1 and the open circuit voltage (VOC) of the polythiophene-based solar cells in which the derivatives 1 are utilized as an acceptor material. This fact suggests that the VOC of the solar cells is subjected to the LUMO level of the derivatives 1. Moreover, the LUMO energy is lowered with increasing the Hammett constant of the substituent on the benzene ring in the derivatives 1. Therefore, we can predict the relative value of the VOC in the polythiophene-based solar cells.