Amorphous Ternary Charge-Cascade Molecules for Bulk Heterojunction Photovoltaics

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Ternary bulk heterojunctions are key for organic solar cell efficiency.
• Controlling self-assembly in solution-processed ternary blends is challenging.
• Spiro linkers can control molecular semiconductor crystallinity.

Purpose of the Study:

• To demonstrate a strategy for controlling self-assembly in ternary blends.
• To synthesize spirobifluorene (SF) derivatives for organic solar cells.
• To investigate the effect of SF derivatives on organic solar cell performance.

Main Methods:

• Synthesis of SF-(DPP)4 and SF-(PDI)4 derivatives.
• Fabrication of ternary blend organic solar cells with P3HT:PCBM host.
• Characterization using differential scanning calorimetry, X-ray/electron diffraction, quantum efficiency, and impedance spectroscopy.

Main Results:

• Low loadings (1 wt%) of SF derivatives improved PCE by 36% (2.5% to 3.5%).
• Improvements attributed to increased fill factor and open-circuit voltage.
• Higher loadings decreased PCE due to reduced short-circuit current density.

Conclusions:

• SF derivatives are excluded to the donor:acceptor interface by host blend crystallization.
• This interfacial localization enhances charge carrier lifetime and device performance.
• The strategy offers a pathway to optimized charge-cascade morphology in organic solar cells.