Pseudo-Solid-State Polymer Materials for QD-Sensitized NIR-I and NIR-II Upconversion Beyond the Silicon Bandgap

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Quantum-dot (QD) sensitized triplet-triplet annihilation upconversion (TTA-UC) is promising for harvesting sub-bandgap photons in silicon photovoltaics and infrared photodetectors.
• Translating solution-based TTA-UC to solid-state systems faces significant efficiency losses.
• Maintaining liquid-like dynamics in a solid form is crucial for efficient upconversion.

Purpose of the Study:

• To develop a robust solid-state TTA-UC system using QD sensitizers.
• To overcome efficiency losses associated with solid-state upconversion methods.
• To enable efficient harvesting of near-infrared (NIR) photons for optoelectronic applications.

Main Methods:

• Encapsulation of QD-sensitized upconversion mixtures into mesoscale droplets within a rigid acrylate matrix.
• Utilizing a PbS sensitizer, carboxytetracene mediator, and TES-ADT annihilator system.
• Employing transient absorption spectroscopy to confirm QD surface chemistry and dynamics.

Main Results:

• Achieved record-high normalized UC emission efficiency (η_UC) of 0.72% and upconverted singlet state generation efficiency (η_UCs) of 18% in the NIR-I regime (785 nm excitation) for solid-state QD-sensitized systems.
• Demonstrated the first quantifiable solid-state TTA-UC in the NIR-II regime (1064 nm excitation) with η_UC of 0.022% (η_UCs of 0.55%).
• Developed a chemically compatible polymer system enabling spontaneous QD phase separation into nanodroplets, preserving QD surface chemistry and preventing significant efficiency drops.

Conclusions:

• The hybrid approach successfully preserves liquid-like dynamics in a pseudo-solid form, enabling high-efficiency solid-state TTA-UC.
• This method overcomes major challenges in solid-state upconversion, paving the way for practical applications.
• The findings represent a significant advancement towards integrating QD-sensitized TTA-UC into silicon-based optoelectronics.