Charge transport (CT) in soft condensed matter is at the heart of many exciting and potentially revolutionising technologies ranging from organic photovoltaic cells to nanobioelectronic transistors. Yet, our fundamental understanding of CT in organic and biological semiconductors (OBS) that could rationalise experimental observations and guide further advances in the field is still very limited. These materials are characterised by strong, anharmonic thermal fluctuations and small energy barriers for CT, which renders standard theories such as band theory or activated electron hopping in many cases entirely inadequate. In this project I propose the development of a disruptive computational method‚ based on non-adiabatic molecular dynamics (NAMD), that will open the door for ground-breaking new insight into this problem.
This problem is important for society because organic semiconductors (OS) are an exciting class of materials that have the potential to enable disruptive technologies in the renewable energy sector and in the plastic electronics industry. Leight-weight, flexible and relatively easy to produce from renewable resources, OS combine many desirable materials properties for thin film electronic devices. They have already found first applications in organic photovoltaic devices (OPV), organic light-emitting diodes and flexible displays, and they are envisioned in many other applications as well, such as e-paper and radio-frequency identification tags. Their potential future importance is reflected by the global market for OS forecasted to rise from 20 bn US$ in 2012 to 330 bn US$ in 2027 with OPV devices identified as one of the main areas for growth.
The objectives of the project are
(1) the development of a fast non-adiabatic molecular dynamics (NAMD) method enabling
(2) new fundamental insight into the nature of charge transport in ultrapure single crystalline OS.
The novel simulation methodology will then be used to
(3) establish structure-charge mobility relationships in OS from the bottom-up to understand how disorder, defects and interfaces between crystalline and amorphous domains impact on the quantum mechanical propagation of the excess charge.
The knowledge obtained in (2) and (3) will be used to
(4) guide the development of high dielectric-high mobility hybrid inorganic/organic materials.
Finally, I aim at expanding the methodology to biological systems, specifically to
(5) CT in bacterial nanowire proteins, to identify common principles and differences between man-made and native semiconducting structures.
In conclusion, I consider the fragment orbital-based surface hopping (FOB-SH) non-adiabatic molecular dynamics methodology developed a breakthrough in the computer simulation of non-adiabatic processes in molecular materials. The methodology pushed the state-of-the-art of non-adiabatic molecular dynamics simulation from the molecular to the true nanoscale. Applications of FOB-SH have led to a new understanding of the nature and dynamics of charge carriers in organic molecular materials, which we termed ``transient delocalization mechanism”. The methodology also proofed very useful for establishing design rules for new high-mobility organic semiconductors and for molecular-scale understanding of the impact of microstructure on carrier mobility. The development of the FOB-SH method was planned but it’s efficiency, success and practical usefulness exceeded my expectations.
