Editing solar energy to surpass the Shockley-Queisser limit by aggregation induced emission (AIE)-sensitized lanthanides energy conversion

Collaborative Research Program for 2022-2024

We propose developing new generation, highly efficient up/down-converting materials, using new sensitization pathways to harvest NIR/UV light over a broad spectral range and subsequent efficient conversion luminescence by AIE photo-sensitizer. This research program will optimize the energy transfer process from singlet or triplet states of a broadband light-harvesting AIE LPs to Ln ion through the long-lived triplet state of the LPs and Ln loaded metal-organic framework (MOF) in the AIE host. These optical energy transformers hold great promise to surpass the Shockley-Queisser limit in solar cells. The proposed research will also establish the design principles, robust synthetic, and assembly approach to develop future high-priority technologies. In this research program, scientific issues and our proposed innovative strategies are:
1. Low and narrow absorption due to the nature of f-f transition and the low up/down-conversion efficiency. We will design and synthesize AIE LPs with broad absorption in UV (or short wavelength visible) and NIR to overcome it. They will have two functional groups to make coordination bonds with Ln ions. With AIEsensitization, we can solve the absorption issues and thus improve the energy conversion performance, ultimately.
2. Limited sensitization area only nearby the surface of NPs, which limits the sensitization efficiency. To address this issue, we will introduce an Ln-AIE MOF system, where Ln ions are incorporated into the AIE matrix by coordination bonds to realize collective up/down-conversion with minimizing loss in the energy transfer. Bifunctional AIE LPs will be a ligand in the MOF to form the framework with Ln ions and sensitize all the ions in the vicinal position.
3. The short lifetime of the singlet state, preventing an efficient energy transfer from the molecular donor to an Ln ion. To overcome this, we will introduce thermally assisted delayed fluorescence (TADF) and room temperature phosphorescence (RTP) concept, which involves a long-lived triplet state in their excitation state. Some OTP materials and AIE-TADF materials can hold a promising property with higher photostability and without a concentration quenching issue.
4. The low photostability of conventional organic dyes under continuous illumination of light. The low photostability mainly originates from oxidation by the triplet excited state of the dye promoting reactive oxygen species generation. Thus, to address this issue, we should consider the trade-off between photostability and utilization of triplet excitation state. J-aggregation of dye for some AIE LPs potentially reduces the formation quantum yield of the triplet state of the dye, which can suppress the photodegradation of dyes [J. Phys. Chem. B 2008, 112, 836-844]. So far, for AIE-TADF materials, there has been no report about the photostability issue, which is attributable to a buffering effect of condensed material.
We shall use multi-scale modeling to calculate the relevant energy transfer parameters for further guiding the developments of energy-converting materials.