Issue 3, 2024

Enthalpy-uphill exciton dissociation in organic/2D heterostructures promotes free carrier generation

Abstract

Despite the large binding energy of charge transfer (CT) excitons in type-II organic/2D heterostructures, it has been demonstrated that free carriers can be generated from CT excitons with a long lifetime. Using a model fluorinated zine phthalocyanine (F8ZnPc)/monolayer-WS2 interface, we find that CT excitons can dissociate spontaneously into free carriers despite it being an enthalpy-uphill process. Specifically, it is observed that CT excitons can gain an energy of 250 meV in 50 ps and dissociate into free carriers without any applied electric field. This observation is surprising because excited electrons typically lose energy to the environment and relax to lower energy states. We hypothesize that this abnormal enthalpy-uphill CT exciton dissociation process is driven by entropy gain. Kinetically, the entropic driving force can also reduce the rate for the reverse process – the conversion of free electron–hole pairs back to CT excitons. Hence, this mechanism can potentially explain the very long carrier lifetime observed in organic/2D heterostructures.

Graphical abstract: Enthalpy-uphill exciton dissociation in organic/2D heterostructures promotes free carrier generation

  • This article is part of the themed collection: #MyFirstMH

Supplementary files

Article information

Article type
Communication
Submitted
22 sep. 2023
Accepted
20 nov. 2023
First published
20 nov. 2023

Mater. Horiz., 2024,11, 813-821

Enthalpy-uphill exciton dissociation in organic/2D heterostructures promotes free carrier generation

F. Rudayni, K. Rijal, N. Fuller and W. Chan, Mater. Horiz., 2024, 11, 813 DOI: 10.1039/D3MH01522J

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