Charge transport and open-circuit voltage in semicrystalline polymer solar cells
- Semiconducting polymers have the potential to be used in electronic devices ranging from solar cells to biosensors. These materials offer advantages over traditional inorganic devices that include decreased materials cost, cheaper and low-temperature processing, and the enabling of fully flexible devices on plastic or for incorporation into textiles. However, the performance of organic photovoltaics in particular has not yet reached comparable levels to that of silicon, due to the disordered nature of the polymers and complex interfacial processes within the active layer. In this thesis, I will discuss several sources of inefficient performance in a polymer-fullerene heterojunction film. First, after the absorption of light creates an electron-hole pair, the charges form a charge transfer state at the interface between the polymer and fullerene which fundamentally limits the possible open-circuit voltage (Voc). I experimentally probe the Voc losses in these solar cells and show that populating higher energy interfacial states is not the cause of increases in Voc, but rather that local aggregation or delocalization effects shift the low-energy interfacial state. Extraction of charges via the polymer phase is also the source of significant losses in current as well as in voltage. In particular, the mobility of the polymer phase is often the limiting carrier mobility of the device, and optimizing this mobility holds many applications in organic electronics beyond solar cells. In the latter part of the thesis I focus therefore on understanding the source of traps in pristine semicrystalline polymer films. I develop a model that relates the physical properties and parameters of the semicrystalline material to the charge transport and analyze the effects on transport pathways. Finally, this model is applied to understanding a number of experimentally observed features of charge transport, including the effects of molecular weight and applied electric field.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Mollinger, Sonya Avi
|Stanford University, Department of Applied Physics.
|Spakowitz, Andrew James
|Spakowitz, Andrew James
|Statement of responsibility
|Sonya Avi Mollinger.
|Submitted to the Department of Applied Physics.
|Thesis (Ph.D.)--Stanford University, 2016.
- © 2016 by Sonya Avi Mollinger
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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