Final Defense: Methods for roll-to-roll vapor deposition of organic semiconductors
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Organic semiconductors find their most successful commercial application as organic light emitting devices (OLEDs) displays, and are extensively investigated in other applications, such as photovoltaic cells (OPVs) and thin film transistors (OTFTs) due to their excellent flexibility and tunability. The key to realizing an arguable advantage of organic semiconductors, low cost, is to fabricate thin film organic semiconductor devices on a continuous flexible roll rapidly. This production method, called roll-to-roll (R2R) manufacturing, can be implemented by solution processing or vapor deposition of organic thin films. Despite its advantages in high material purity and device reliability, the R2R vapor deposition of organic semiconductors is less sufficiently researched compared to solution processing due to the necessarily complex equipment and costly material consumption. This thesis aims to investigate critical methods that can be used to develop practical large scale R2R fabrication of organic semiconductors.
The integration of two different vapor deposition methods, vacuum thermal evaporation (VTE) and organic vapor phase deposition (OVPD), to R2R processing is demonstrated in a pilot tool that accommodates 10 cm-wide substrate rolls. The method to achieve ultrahigh deposition rates is demonstrated using OVPD. Uniform organic semiconductor thin films grown at rates as high as 50 Å/s are achieved. A comprehensive numerical model that is capable of simulating complex, multilayer WOLED structures is developed to provide an alternative to experimental iterations of OLED design and tests. A cost estimate on the R2R production of WOLEDs for lighting is developed as an example to demonstrate the framework on cost modelling the large scale R2R production of various organic semiconductor devices, using primarily vapor deposition techniques. With incremental reduction in material and driver costs, and improved luminance, the cost of WOLED lighting can be reduced to $6.3 /klm in the near term, positioning WOLEDs for use in numerous premium lighting applications.