Metal Bistriflimide Doping of MEH-PPV: Linking Ionic Crosslinking to Enhanced Conductivity and Stability

The incorporation of metal bistriflimide (M(TFSI)_n) salts into conjugated polymers provides a tunable approach to control charge transport and film morphology through coordination-driven interactions. Here, we examine MEH-PPV doped with LiTFSI, Zn(TFSI)₂, and La(TFSI)₃ to elucidate how metal valency and ionic size influence structural reorganization and conductivity. Spectroscopic analysis (FTIR, Raman, and XPS) reveals coordination of metal cations to ether and carbonyl oxygens, forming ionic crosslinks that promote film densification and improve both stability and electronic conductivity. La(TFSI)₃ induces the strongest coordination, resulting in a smooth, uniform morphology and conductivity enhancements exceeding 10^-3 S cm^-1 with improved ambient stability. XPS O 1s and C 1s shifts confirm electron density withdrawal upon coordination, while optical measurements show preserved π–π interactions. These findings establish a clear structure–property relationship between ion coordination and charge transport, underscoring metal bistriflimide doping as a promising route to stable, high-conductivity polymer thin films for optoelectronic applications.