On the Effective Temperature Concept in Disordered Materials

While semiconductors are a cornerstone of modern technology, a few highly ordered materials dominate. Although more disordered systems, such as conjugated organic molecules or quantum dot solids, promise more flexibility and reduced cost, their performance is often still limited, and many aspects of carrier conduction are not fully understood. This thesis focuses on the effects of high electric fields on charge transport. Simulations suggest that, when exposed to high fields, the carrier distribution in disordered materials shifts analogous to an elevated ‘effective’ temperature. Experimental evidence of this is, however, scarce and only, indirectly, probes the resulting change in carrier mobility. The main goal of this thesis is to provide direct experimental evidence for an effective temperature carrier distribution by measuring the Seebeck voltage generated between high- and low-field regions in relevant disordered materials. To validate this new method, it was rigorously tested for interfering side effects and applied to organic and inorganic materials. By comparing to and combining with established methods, the physical reality of an effective temperature distribution was confirmed. This knowledge is not only important for academic understanding and improving existing devices, but might also open a pathway to new field driven thermoelectric applications.