Redox Doping of Polymer Blend Solar Cells to Improve TEM Imaging of Nanoscale Morphology
Polymer blend solar cells (PSC) have an advantage over traditional organic solar cells in that they do not contain a fullerene-derived acceptor material. By removing this material, PSCs can be manufactured at a lower cost and may exhibit better temporal stability. At this time, the efficiency of PSCs is not as high as devices containing a fullerene derivative. One approach to improving the efficiency of PSCs is to understand and actively control the nanoscale morphology of the polymer blend. Transmission Electron Microscopy (TEM) is used to great effect in the imaging of traditional organic solar cells because domains of the fullerene derivative have a greater electron density than the surrounding polymer and thus good phase contrast is achieved. Unfortunately, in PSCs, the two materials are of similar electron density which makes it difficult to achieve the necessary level of phase contrast. This project will employ redox doping, either in solution or electrochemically, to enhance the phase contrast of TEM images of polymer blend films. Similar to the doping of block copolymer films with OsO4, this approach will selectively p- (or n-) dope the donor (or acceptor) domains of polymer blend thin films to improve electron density/conductivity which will provide improved phase contrast in TEM images. The level of doping, p- vs. n- doping, and polymer blend composition will all be studied and correlated with photovoltaic properties. This work may lead to an improvement in the efficiency of PSCs and bring their performance closer to that of other photovoltaic technologies.
Final product of lasting value:
Advisor: Samson Jenekhe, Chemical Engineering