Symmetry-Breaking Charge Separation in the Solid State: Tetra(phenoxy)perylenediimide Polycrystalline Films

Area of Science:

• Materials Science
• Photovoltaics
• Organic Electronics

Background:

• Electron-hole pair generation via symmetry-breaking charge separation (SB-CS) is key for boosting organic photovoltaic (OPV) open-circuit voltage.
• Previous studies primarily focused on molecular dimers in solution, limiting applicability to solid-state devices.

Purpose of the Study:

• Investigate SB-CS in polycrystalline thin films of 1,6,7,12-tetra(phenoxy)perylene-3,4:9,10-bis(dicarboximide) (tpPDI).
• Compare SB-CS efficiency between films with n-octyl groups (octyl-tpPDI) and hydrogen atoms (H-tpPDI) on imide nitrogen atoms.

Main Methods:

• Thin film fabrication of octyl-tpPDI and H-tpPDI.
• X-ray diffraction and scattering for structural analysis.
• Transient absorption spectroscopy to probe excited-state dynamics.

Main Results:

• Both octyl-tpPDI and H-tpPDI films exhibit π-π stacking.
• H-tpPDI displays more slip-stacked arrangements and intermolecular hydrogen bonds compared to octyl-tpPDI.
• Octyl-tpPDI shows mixed singlet excited and charge transfer states (excimer-like).
• H-tpPDI demonstrates nearly quantitative SB-CS.

Conclusions:

• Molecular packing and intermolecular interactions significantly influence SB-CS efficiency in tpPDI films.
• H-tpPDI's structure facilitates efficient SB-CS, making it a promising material for advanced organic photovoltaic applications.