van der Waals solid solution crystals for highly efficient in-air photon upconversion under subsolar irradiance.

Area of Science:

• Materials Science
• Photochemistry
• Solid-State Physics

Background:

• Photon upconversion (UC) offers broad applications but is limited by poor exciton transport in solid materials due to low crystallinity and sensitizer aggregation.
• Developing high-performance solid-state UC materials requires overcoming challenges related to molecular organization and energy transfer.

Purpose of the Study:

• To demonstrate the effectiveness of the van der Waals solid solution concept for creating superior molecular crystals for photon upconversion.
• To address the limitations of sensitizer aggregation and poor exciton transport in solid UC materials.

Main Methods:

• Incorporating a porphyrin sensitizer at 0.001% into ANNP (a blue-fluorescent hydrocarbon annihilator with bulky side groups) via recrystallization.
• Utilizing the van der Waals solid solution approach to form millimeter-sized, uniformly colored, transparent molecular crystals.
• Annealing the resulting crystals to enhance their upconversion performance.

Main Results:

• Formation of millimeter-sized, transparent, and uniformly colored solid solution crystals, effectively preventing sensitizer aggregation.
• Achieved unprecedented UC performance, including a UC quantum yield of 16% (50% theoretical max), a low excitation intensity threshold of 0.175 sun, and high photostability (>150,000 s) in air.
• Demonstrated the significant advantages of the van der Waals solid solution concept for superior UC material development.

Conclusions:

• The van der Waals solid solution concept is highly effective for fabricating high-performance solid-state photon upconversion materials.
• This strategy successfully resolves the issue of sensitizer aggregation, paving the way for advanced UC applications.
• The developed molecular crystals exhibit extraordinary UC efficiency and stability, marking a significant advancement in the field.