PhD candidate Department of Materials Science and
Engineering Technion, Israel Institute of Technology, Haifa, 32000 ISRAEL
The heart of every organic solar cell is the donor/acceptor bulk heterojunction (BHJ). The complex morphology of the BHJ, composed of both ordered and disordered domains, dictates device performance and efficiency. In addition to challenges in controlling the morphology, its characterization is also complicated, mainly because the disordered domains are silent to most analytical tools. To overcome this challenge, we have developed a new analytical tool to probe the complex blend morphology based on exposing the thin organic films to sequences of ZnO atomic layer deposition (ALD).
Applying ALD onto organic films, unlike conventional inorganic substrates, may lead to precursor infiltration into the sample and sub-surface deposition. By varying the deposition conditions and altering the crystallinity of the nonreactive organic film, we have investigated the mechanism of sub surface deposition. Subsequently, we harness the subsurface ALD to study the morphology evolution in a series of P3HT/fullerene blends commonly used for processing OSC BHJ. This mapping methodology allowed us to map the disordered domains throughout the BHJs, to follow the vertical distribution of the components and to estimate the solubility limit of the fullerene. This methodology provided significant insights into the correlation between morphology evolution and device performance that are unattainable in conventional characterization tools. Finally, we show the feasibility of subsurface deposition as a pathway to fabricate hybrid organic inorganic photovoltaic devices.
Supervisor: Prof. Gitti L. Frey