Effect of side chain length on photovoltaic performance of fused-ring electron acceptors

Abstract

A series of ITIC analogues with varying alkyl groups on the phenyl side chains were synthesized, and effects of the alkyl length on photovoltaic performance of the ITIC series were studied. Increasing alkyl length from pentyl to decyl slightly down-shifts highest occupied molecular orbital energy level and up-shifts lowest unoccupied molecular orbital energy level. In the solution, the absorption spectra of these six molecules are almost same, but those in the films slightly blue-shift with increasing the alkyl length. Electron mobility of the ITIC series gradually decreases with increasing the alkyl length. Organic solar cells based on J71: ITIC series blends were fabricated. With increasing the alkyl length of the ITIC series, open-circuit voltage slightly increases, short-circuit current density gradually decreases, fill factors are 65.4% ~ 68.4%, power conversion efficiencies are 9.79% ~ 10.2%, and the ITIC derivatives with C6, C7 and C8 side chains yield higher values of 10.1% ~ 10.2%.