Electronic states and molecular orientation of ITIC film

TL;DR

This study investigates the electronic states and molecular orientation of ITIC films, revealing key energy levels and orientation preferences that underpin their high performance in organic solar cells.

Contribution

It provides detailed measurements of energy levels and molecular orientation of ITIC films, enhancing understanding for photovoltaic material design.

Findings

Negative charge transfer level at 4.00 eV below vacuum

Ionization potential of 5.75 eV

Predominantly face-on molecular orientation on smooth substrates

Abstract

ITIC is the milestone of non-fullerene small molecule acceptors used in organic solar cells. We have studied the electronic states and molecular orientation of ITIC film using photoelectron spectroscopy and X-ray absorption spectroscopy. The negative integer charge transfer energy level is determined to be 4.00 plus or minus 0.05 eV below the vacuum level, and the ionization potential is 5.75 plus or minus 0.10 eV. The molecules predominantly adopt the face-on orientation on inert substrates as long as the surfaces of the substrates are not too rough. These results provide physical understanding of the high performance of ITIC-based solar cells, also afford implications to design more advanced photovoltaic small molecules.