Controlling the interfacial dipole via functionalization of quinoxaline-based small molecules for electron transport layer in organic light emitting diodes

Figures & data

Figure 1. (a) Chemical structures of QPSMs, (b) device configuration, (c) chemical structures of SY, and (d) synthesis schemes for the QPSMs.

Figure 2. (a) TGA thermograms, (b) DSC thermograms, and (c) XRD data of QxTPPO1, MQxTPPO1, and FQxTPPO1, (d) UV-vis spectra in the chloroform solution, (e) CV curves of QxTPPO1, MQxTPPO1, and FQxTPPO1, and (f) Energy diagrams of all materials in the OLEDs.

Table 1. Optical and electrochemical properties of QPSMs.

Polymer	${\lambda }_{max}^{abs}$ (nm)^a	$E_{gap}^{opt}$(eV)^b	HOMO (eV)^c	LUMO (eV)^d	$E_{gap}^{elec}$ (eV)^e
QxTPPO1	349	3.18	−6.22	−3.00	3.22
MQxTPPO1	379	2.98	−6.08	−3.01	3.07
FQxTPPO1	352	3.15	−6.37	−3.27	3.10

Note: ^aMaximum absorption peak in the chloroform solution; ^bEstimated from Tauc plot in thin film state; ^cEstimated by the oxidation onset potential; ^dEstimated by the reduction onset potential; ^eCalculated by the oxidation and reduction onset potentials in the CV curves.

Figure 3. (a) Optimized geometry with the value of dipole moment of QxTPPO1, MQxTPPO1, and FQxTPPO1, (b) Schematic images of interfacial dipole moment and (c) Cathode work functions with and without ETL (scanning Kelvin probe measurement).

Figure 4. Device performance of OLEDs with QPSMs; (a) J-V curves, (b) L-V curves, (c) LE-L curves, and (d) EQE-L.

Table 2. Summarized device performance for OLEDs.

Device configuration(OLEDs)	L max [cd/m2] @ bias	LE max [cd/A] @ bias	EQE max [%] @ bias	Turn-on Voltage [V] @ 1cd/m2
ITO / PEDOT:PSS / SY / Al	1633@9.7	0.72@9.4	0.16@9.4	4.0
ITO / PEDOT:PSS / SY / QxTPPO1 / Al	6211@9.1	16.69@4.3	5.65@4.3	2.5
ITO / PEDOT:PSS / SY / MQxTPPO1 / Al	10030@8.8	17.98@4.3	6.12@4.3	2.5
ITO / PEDOT:PSS / SY / FQxTPPO1/ Al	3723@10.5	8.76@4.8	2.94@4.8	2.5

Figure 5. (a) Atomic force microscopy (AFM) images and (b) Contact angles on the SY with and without QSPMs such as QxTPPO1, MQxTPPO1 and FQxTPPO1.