(In)validating the KPFM Method for Estimating the Trap Density of States in Organic Semiconductors
Date
2025-03-05
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Abstract
Due to the complex structure of organic semiconductors, accurately estimating the trap density of states (DOS) within these materials is a challenge. In the past few decades, multiple techniques have been developed that estimate traps in organic materials. However, each technique has some limitations. This thesis focuses on improving our understanding of one less commonly used technique that employs Kelvin Probe Force Microscopy to measure the surface potential of a thin semiconducting film. We used OghmaNano to simulate this measurement of trap DOS within P3HT, a p-type material. OghmaNano computationally solves the drift-diffusion equation and incorporates non-equilibrium Shockley-Read-Hall formulism, which describes the physics of carrier traps in these materials. Our analysis employs analytical equations derived by previous groups that relate the density of states to the surface potential of a thin film as a gate voltage is changed. While this technique has been employed experimentally, the trap DOS was not known in those materials. In our simulations, we define the trap DOS, run the simulation to calculate the potential, and then apply the analysis used by others. We are unable to extract the correct trap DOS. We investigate the reason for this, examining the role of temperature and whether our use of SRH trap dynamics is sufficient to explain the difference. We were not able to conclusively determine the cause at this time.
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Ogranic Semicondcutors, Density of States, Traps, Kelvin Probe Force Microscopy, OghmaNano simulation