Recovering nanoscale morphological parameters of organic semiconductors using carrier transport measurement methods

Charge carrier transport measurements are commonly used to study electronic materials. For organic electronic devices including LEDs, photovoltaic cells and photodetectors, such measurements are used to probe charge carrier mobilities in the organic semiconductor
involved. The extracted mobilities bear important relevance to device performance. In OLEDs, knowledge of mobility allows the estimation of the light-emitting recombination zone, and in OPV cells to determine whether both electron and hole mobilities are balanced or not. Charge transport data, however, carry rich information about the material under investigation beyond mobility values. As carriers migrate inside a material, they sample not only the energetic landscape but also the nanoscale environment and connectivity of conducting domains. Thus, the mobility must be influenced also by the nano-scale chemical structure and morphology. Here, we propose that by conducting a table-top temperature dependent transport measurements on organic semiconductors and analyzing the data with desired transport model, one will be able to acquire not only the standard mobility data, but also two additional metrics which are related to (i) the packing distance information between adjacent molecules, and (ii) the positional / geometric randomness of the molecules or polymers in the organic semiconducting films. The theoretical machinery that enables us to do such delineation originates from the well-known Gaussian Disorder Model (GDM). Several model systems involving small molecules will be tested to demonstrate the data extraction process. The results will be cross-validated against structural characterization using X-Ray techniques for (i), and highly sensitive EQE characterization technique for (ii). Additional validation will be provided by X-ray techniques and computationally by molecular dynamic simulations via our collaborators. Applications of transport measurements to some semiconducting polymers and high-performance non-fullerene acceptors will be discussed. The outcome of this proposal will provide a table-top alternative to characterize organic semiconductors and simply material characterization process.