Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 24, Issue 8, Pages 1100-1108Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201301810
Keywords
conjugated polyelectrolytes; ionic motion; work function tuning; organic electronics
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Funding
- Core Technology Development Program for Next-Generation Solar Cells of the Research Institute for Solar and Sustainable Energies (RISE) at GIST
- National Research Foundation (NRF) of Korea [2008-0093869, 2008-0062606 (CELA-NCRC), 2012R1A1A2005855, 2012R1A2A2A06045327]
- National Research Foundation of Korea [2012R1A1A2005855, 2008-0093869, 10Z20130000004, 2012R1A2A2A06045327] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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Despite the excellent work function adjustability of conjugated polyelectrolytes (CPEs), which induce a vacuum level shift via the formation of permanent dipoles at the CPE/metal electrode interface, the exact mechanism of electron injection through the CPE electron transport layer (ETL) remains unclear. In particular, understanding the ionic motion within the CPE ETLs when overcoming the sizable injection barrier is a significant challenge. Because the ionic functionality of CPEs is a key component for such functions, a rigorous analysis using highly controlled ion density (ID) in CPEs is crucial for understanding the underlying mechanism. Here, by introducing a new series of CPEs with various numbers of ionic functionalities, energy level tuning at such an interface can be determined directly by adjusting the ID in the CPEs. More importantly, these series CPEs indicate that two different mechanisms must be invoked according to the CPE thickness. The formation of permanent interfacial dipoles is critical with respect to electron injection through CPE ETL ( 10 nm, quantum mechanical tunneling limit), whereas electron injection through thick CPE ETL (20-30 nm) is dominated by the reorientation of the ionic side chains under a given electric field.
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