Is a Single Molecule Sufficient to Determine the Internal Charge Trapping Energy in Crystalline Organic Semiconductors?

In silico diagnoses of charge-transfer efficiencies in organic semiconductors require the accurate computations of transport parameters. We show here that ignoring the molecular packing effects when computing the internal charge trapping energy may cause a severe deviation to the result deduced from the periodic crystal structure. This deviation can reach up to 100 meV in common organic materials. According to the semiclassical Marcus theory, this energy difference can lead to orders of magnitude change in the charge transfer rate. Studying from a total of 45 organic crystals, we find that single-molecule approximation though is adequate for rigid planar molecules yet it fails to describe the trapping energy for molecules that have inter-ring single bond(s) or are subjected to planarity changes during the transition from the isolated state to the embedded state. These results and conclusions may shed light on the removal of theory-experiment discrepancies on charge mobilities and lay the basis for the future fast and precise screening of high-performance organic semiconductors.