Harvesting triplet excitons and enhancing emission for photon upconversion using optical cavities Robert Gordon, Ravi Kumar Venkatraman, Robert Oliver, Peter Claronino, Jenny Clark University of Sheffield, UK More than 20% of the solar irradiance at Earth lies in the infrared region and cannot be harvested by high- bandgap (>1.1 eV) solar cells. This is because infrared photons have energies which are lower than the bandgap of these solar cells and pass straight through the device. One way to capture this lost energy is to up-convert pairs of infrared photons into higher energy visible photons. This photon-up conversion process can be achieved practically using organic semiconductors which undergo triplet-triplet annihilation (TTA). Unfortunately, the upconversion efficiency is low in the solid state and must be improved to be applicable to devices. Here we propose a method for enhancing the extraction of upconverted photons in the solid state by placing rubrene, an organic semiconductor previously used for upconversion, 1 into an optical cavity. We find the newly formed “bright” polariton state exhibits a tunable emission wavelength which has a greater intensity compared to the bare film. The cavities also show an enhanced delayed emission usually associated with TTA, making them a promising tool for harvesting upconverted photons. 2 To understand this phenomenon we implemented ultra-fast time-resolved spectroscopy which shows the triplet exciton population is longer lived inside the cavity, suggesting the enhanced emission originates from annihilation of triplet excitons. These results lay the foundations of a tunable photon upconversion system that can be used in tandem with solar harvesting devices. References 1. D. G. Bossanyi, Y. Sasaki, S. Wang, D. Chekulaev, N. Kimizuka, N. Yanai and J. Clark, J.Mater.Chem.C., 2022, 10 , 4684–4696. 2. D. Polak, R. Jayaprakash, T. P. Lyons, L. Á. Martínez-Martínez, A. Leventis, K. J. Fallon, H. Coulthard, D. G. Bossanyi, K. Georgiou, A. J. Petty, II, J. Anthony, H. Bronstein, J. Yuen-Zhou, A. I. Tartakovskii, J. Clark and A. J. Musser, Chem. Sci., 2020, 11 , 343–354.
PC03
© The Author(s), 2023
Made with FlippingBook Learn more on our blog