Unmixed Planar Heterojunction Interfaces Enabling Exceptional Air Stability in Organic Photodetectors

Area of Science:

• Organic electronics
• Materials science
• Device physics

Background:

• Bulk heterojunction (BHJ) and pseudo-planar heterojunction (PHJ) organic photodetectors (OPDs) face challenges with nanomorphology instability, impacting air stability.
• Partially mixed interfaces in conventional PHJ OPDs degrade performance and longevity.
• Developing air-stable OPDs is crucial for their practical implementation.

Purpose of the Study:

• To address the air stability issues in organic photodetectors (OPDs).
• To develop a novel strategy for creating stable immiscible planar heterojunction (PHJ) interfaces.
• To demonstrate high performance and exceptional air stability in the fabricated OPDs.

Main Methods:

• Utilized a random polythiophene (RP-T50) with thermocleavable side chains (TCSs) as the electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor.
• Applied thermal annealing to cleave TCSs, rendering RP-T50 insoluble and forming stable, unmixed PHJ interfaces.
• Employed all-green-solvent processing for device fabrication.

Main Results:

• Achieved high performance metrics: responsivity ≈138 mA W⁻¹, specific detectivity ≈1.68 × 10¹² Jones, and a linear dynamic range ≈100 dB (unbiased).
• Demonstrated exceptional air stability, with devices maintaining performance for ≈250 days in ambient conditions without encapsulation.
• Successfully prevented the formation of performance-degrading pseudo-PHJ interfaces.

Conclusions:

• A simple and scalable strategy using thermocleavable side chains effectively enhances OPD air stability.
• The developed insoluble donor material enables robust PHJ interfaces, overcoming nanomorphology instability.
• This approach holds significant potential for the commercialization of organic photodetectors.