Effects of pn Doping in Thiophene/Phenylene Co-oligomers Thin Films

Abstract

Doping effects in thiophene/phenylene co-oligomers (TPCOs) have been studied by means of extreme-UV (EUV) excited photoelectron spectroscopy (EUPS) and electro-luminescence experiments. Doped poly-crystalline films were fabricated by p-type doping with MoO₃ to inherent p-type TPCO, BP1T (2,5-bis(4-biphenylyl)thiophene), and by n-type doping with Cs₂CO₃ to n-type AC5-CF₃ (1,4-bis{5-[4-(trifluoromethyl)phenyl]thiophen-2-yl}benzene), respectively. Doping concentrations were 2% in both cases. The work function of BP1T was shifted from 4.0 to 4.3 eV and that of AC5-CF₃ was shifted from 4.8 to 3.9 eV. The energy shifts are reasonable directions for p- and n-type doping. We also confirmed higher current injection with the doping films.

Keywords:

• Thiophene/phenylene co-oligomers
• organic laser
• pn doping
• EUPS
• organic EL

Acknowledgments

This work was partly supported by JSPS KAKENHI Grant Numbers 22560017 and 25390060.