Novel Computational Method Used in the Development of Models Describing Charge Carrier Mobility Within Organic Semiconductors
Open Access
- Author:
- Donaher, Shane
- Area of Honors:
- Materials Science and Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Scott Thomas Milner, Thesis Supervisor
Amy Carol Robinson, Thesis Honors Advisor - Keywords:
- Organic Semiconductors
Semiconducting Polymers
Charge Carrier Mobility
Hopping Matrix Element
Electronic Coupling
Transfer Integral
Poly(3-hexylthiophene)
P3HT - Abstract:
- Organic semiconductors offer a plethora of benefits that could allow for drastic improvements to electronic devices within society. They notably show potential for applications within light-emitting diodes, photovoltaic cells, and metal-oxide-semiconductor field-effect transistors. However, the abnormally low charge carrier mobility found within these materials has long been a barrier limiting their prominence. The theory describing charge carrier mobility within organic semiconductors is different than that for inorganic materials. Specifically, the lack of bonding between nearby molecules requires particular quantum conditions to be met for an electron to “hop” from one molecule to the next to move throughout the material. One parameter that plays a significant role in determining the rate at which charge carriers move between molecules is known as the hopping matrix element. The hopping matrix element t quantifies the quantum-mechanical coupling between frontier orbitals on a pair of nearby molecules. Convenient and generally applicable methods to determine t from DFT calculations are lacking; t can be obtained from coupling-induced energy splittings only if the interacting molecules are identical and symmetrically placed. We present a simple approach to determine t from DFT results that relies on measuring hybridization, projecting hybridized pair orbitals onto constituent frontier orbitals of the interacting molecules, using spatially discretized wavefunctions (“cube files”) rather than analytical representations. We demonstrate the method by exploring how t depends on the identity and relative placement of typical moieties found in semiconducting polymers.