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Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light

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Two to One: Entropic Considerations in Upconversion.

Tomi K Baikie^1,2, Oliver Nix^2,3, Marc A Baldo²

¹Cavendish Laboratory, University of Cambridge, Cambridge, U.K. CB3 0US.

The Journal of Physical Chemistry Letters

|July 10, 2025

Summary

This summary is machine-generated.

Photon upconversion requires energy expenditure, necessitating an emission wavelength downshift for efficiency. Maximum upconversion efficiency depends on photon flux, a key thermodynamic consideration for designing molecular systems.

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Area of Science:

Nonlinear Optics
Thermodynamics
Materials Science

Background:

Photon upconversion converts low-energy photons to higher energies, with applications in bioimaging, optogenetics, 3D printing, and photoconversion.
A thermodynamic requirement for energy expenditure exists when decreasing photon number during upconversion.

Purpose of the Study:

To investigate the thermodynamic constraints on photon upconversion efficiency.
To identify a previously overlooked design parameter for efficient molecular upconversion systems.

Main Methods:

Thermodynamic analysis of the photon upconversion process.
Comparison of theoretical predictions with experimental upconversion data.

Main Results:

The second law of thermodynamics mandates an approximate 80 nm emission wavelength downshift (Stokes shift) for practical upconversion under reasonable photon flux.
Maximum upconversion efficiency is inherently dependent on photon flux.
This flux dependence aligns with existing experimental observations.

Conclusions:

Thermodynamic demands dictate that efficient upconversion systems require a specific wavelength downshift at a given input flux.
This wavelength downshift is a crucial, previously overlooked design parameter for molecular upconversion.