Charge Carrier Formation following Energy Gap Law in Photo-Activated Organic Materials for Efficient Solar Cells

Aniket Rana (), Nikita Vashistha, Amit Kumar, Mahesh Kumar () and Rajiv K. Singh ()
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Aniket Rana: Department of Chemistry, Imperial College London, London W12 0BZ, UK
Nikita Vashistha: Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, New Delhi 110012, India
Amit Kumar: Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, New Delhi 110012, India
Mahesh Kumar: Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, New Delhi 110012, India
Rajiv K. Singh: Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, New Delhi 110012, India

Energies, 2024, vol. 17, issue 9, 1-19

Abstract: The charge carrier formation and transport in the pristine polymers as well as in the polymer–fullerene blend is still a hot topic of discussion for the scientific community. In the present work, the carrier generation in some prominent organic molecules has been studied through ultrafast transient absorption spectroscopy. The identification of the exciton and polaron lifetimes of these polymers has led to device performance-related understanding. In the Energy Gap Law, the slope of the linear fit gradient (γ) of lifetimes vs. bandgap are subjected to the geometrical rearrangements experienced by the polymers during the non-radiative decay from the excited state to the ground state. The value of gradient (γ) for excitons and polarons is found to be −1.1 eV −1 and 1.14 eV −1 , respectively. It suggests that the exciton decay to the ground state is likely to involve a high distortion in polymer equilibrium geometry. This observation supports the basis of Stokes shift found in the conjugated polymers due to the high disorder. It provides the possible reasons for the substantial variation in the exciton lifetime. As the bandgap becomes larger, exciton decay rate tends to reduce due to the weak attraction between the holes in the HUMO and electron in the LUMO. The precise inverse action is observed for the polymer–fullerene blend, as the decay of polaron tends to increase as the bandgap of polymer increases.

Keywords: organic solar cell; carrier dynamics; energy gap law (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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