A Phase Diagram of the P3HT:PCBM Organic Photovoltaic System: Implications for Device Processing and Performance

• DOI: 10.1021/ma102524a
• Publication Date: 2011-03-15T16:11:44Z
• Authors: Paul E. Hopkinson; Paul A. Staniec; Andrew J. Pearson; Alan D. F. Dunbar; Tao Wang; Anthony J. Ryan; Richard A. L. Jones; David G. Lidzey; Athene M. Donald
• Keywords: 02 engineering and technology; 0210 nano-technology; 7. Clean energy

This paper describes the construction of a phase diagram for the as-cast state in the organic photovoltaic system P3HT:PCBM. Evidence for a transition to a phase-separated state at PCBM concentrations greater than 70 wt % is seen both by DMTA and GIWAXS, and the glass transition temperatures of blends in the single phase state below 70 wt % PCBM are observed to be raised compared to the pure polymer. Pure PCBM is observed to exhibit a thermal transition at 155 °C, an observation unreported to date—offering insight into crystallites commonly seen in device films. The liquid-crystal phase of P3HT is shown to persist in the presence of up to 41 wt % PCBM. In addition, pure PCBM is shown to be significantly hygroscopic, with important implications for the processing of high-performance devices.