Beyond 1000 nm low-energy sunlight-driven photocatalysis

As one of the most abundant renewable energy sources, sunlight has emerged as a promising substitute for conventional resources, powering applications from photovoltaics to photocatalysis. Yet a substantial portion of its potential remains untapped. Significant progress has been made in visible-light-driven photocatalysis, with recent efforts extending the spectral response to 800 nm. However, unlocking its full potential necessitates innovative paradigms to capture and utilize untapped spectral regions, especially the near-infrared-II (NIR-II, >1000 nm) region, which covers over 20% of solar energy. Moreover, NIR-II light penetrates deeply through solutions due to minimal absorption by substrates, making NIR-II-driven photochemical reactions a promising route for scaling up reaction volumes toward industrial applications. Unfortunately, conventional materials have weak absorption in the NIR-II region, and in addition, the low energy of NIR-II photons limits the formation of high-energy excited states in photocatalysis, making direct use of these photons a challenge.

Recently, Prof. Dai-Wen Pang, together with Prof. Ling Huang and their collaborators, developed an exceptional NIR-II-to-visible upconversion system with a record efficiency of 3.9%, enabling unprecedented large-volume photocatalysis driven by low-energy sunlight with wavelengths beyond 1000 nm. Their findings were published in National Science Review in a paper titled “Beyond 1000 nm low-energy sunlight-driven photocatalysis enabled by quantum dot-based photon upconversion”.

CdS shells with tunable thickness were precisely constructed on the PbS QDs, followed by ligand exchange to anchor the Th-DPP ligands, creating hybrid QDs/Th-DPP NIR-II photosensitizers. Systematic characterization demonstrated that as the CdS shell thickness increased, the triplet lifetime of Th-DPP was substantially prolonged from 0.47 μs to 7.8 μs, while the triplet exciton transfer efficiency decreased from 73.7% to 16.8%. Consequently, an optimal balance was achieved between the triplet lifetime of the ligand and the triplet exciton transfer efficiency, thereby enhancing the overall sensitization performance of this hybrid photosensitizer.

Coupled with rubrene as the annihilator, a record upconversion efficiency of 3.9% was achieved under 1064 nm excitation, which was a 10-fold improvement over previous benchmarks. The efficient quantum dot-based photon upconversion enabled unprecedented large-volume photocatalysis driven only by sunlight with wavelengths beyond 1000 nm for both free radical polymerization and atom transfer radical polymerization, overcoming the spectral limitations of visible-light technologies. The work not only establishes a new paradigm for precise exciton management in quantum dot-based materials but also provides transformative solutions for solar energy harvesting and conversion.

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