**Author details**

#### Ayse Turak

**Figure 6.** Scheme for ITO surface modified by covalently bound HTL materials. Reprinted with permission from [163].

Though dewetting of the active layer is generally undesirable and implicated as a main mechanism in device failure, some groups have harnessed the effect to produce novel device architectures. As many of the films are metastable, they have a natural tendency to dewet into a stable equilibrium form, which can then be used as the starting point for device fabri‐ cation. Developing methods of tuning film morphology and rate of dewetting through total coverage, surface templating and temperature control are of significant interest in forming controlled organic nanostructures. Recently, we [98] used the strong island growth and dewetting tendency of DIP on ITO to produce columnar structures necessary for an interdi‐ gitated ideal bulk heterojunction solar cell, with four orders of magnitude improvement in the device efficiency. Ryu et al. [287] used the energy difference between PEDOT and PFO to form nanoscale dewetted islands of PEDOT at the internal interface in tandem polymer OLEDs. Wang et al. [288] produced sub-micrometer channel OFETs (field effect transistors) using SAM patterned SiO2 to force PEDOT:PSS dewetting. With the PEDOT:PSS acting as the source and drain electrodes, a submicrometer channel of F8T2 polymer was formed. Be‐ nor et al. [289] was able to produce resist patterns of PMMA or PEDOT using selective wet‐ ting on hydrophobic and hydrophilic SAM patterns. Deposition on these patterned substrates lead to the formation of mesoscale patterns for radio frequency ID tags or thin film transistor electrodes. Chen et al. [104] used a similar patterning motif with SAMs that were selectively wet by the two components to encourage phase separation of P3HT:PCBM into an interdigitated columnar structure. Most recently, Harirchian-Saei et al. [290] used the phase separation of PS and PMMA on OTS striped patterns to deliver a periodic array of CdS nanoparticles. By dissolution of the nanoparticle into only one component; then taking

advantage of the selective wetting, a templated nanoparticle array was produced.

This chapter represents a comprehensive summary of the state of the art with regards to in‐ terfacial wetting stability in organic light emitting diodes and organic photovoltaics. Though the challenges are slightly different, both types of optoelectronic devices are heavily influ‐ enced by the stability of the interfaces with the bottom side contact. As organic optoelectron‐

Copyright 2005 American Chemical Society.

246 Optoelectronics - Advanced Materials and Devices

**8. Summary**

**7. Using dewetting as an advantage**

Department of Engineering Physics, McMaster University, Hamilton, Canada
