Ion impurity measurement system LT1000

Introduction

TOYO Corporation has been engineering and marketing a number of test solutions to serve the liquid crystal display (LCD) industry for some time now [1]. LT1000 represents the next generation in the evolution of this product line and the culmination of over twenty years of liquid crystal display measurement research and development work carried out by our engineering teams. It is an ion impurity measurement system that provides a new and innovative method to characterize and measure ion impurity levels of OLEDs, Organic Photovoltaics and other organic materials in a solvent. And the patent-pending system is the first measurement solution of its kind to measure both organic and inorganic ions.

Measurement Principle

Figure 1 shows the equivalent circuit for the impurity measurement. A triangular voltage waveform is applied to the test cell which is injected a solvent with organic materials to be tested, and the displacement current is measured using a current to voltage amplifier and a voltmeter. Measurement data are plotted by voltage versus current characteristics as shown in Figure 2. If there is no ion in a solvent and an organic material, there are two parallel lines having a slope that corresponds to a dielectric constant and a resistivity of a solvent and an organic material. If there are ions in a solvent and an organic material, these ion moves during voltage application and reach the surfaces in a test cell, and detect current peaks as charges, which corresponds to the amount of ion impurity. Normally, there are two current peaks with same amount in positive and negative currents, if a test cell has a symmetric structure.

Figure1

Figure 1 Equivalent circuit for ion impurity measurement of materials in a test cell

Figure2

Figure 2 Schematic representation of triangle waveform voltage vs. current characteristics

Measurement Examples

  1. 1. Organic Photovoltaics [1][2]

    Materials:

    • - P3HT
    • - Supplier difference

    Results:

    • - OPV materials have ion impurities
    • - There is a strong correlation between ion impurities and solar cell efficiencies
    • - LT1000 can be used for screening and QC of OPV materials
    Figure3

    Figure 3 Ion impurity amount comparison in P3HTs

  2. 2. OLED materials [3]

    Materials:

    • - Thermally Activated Delayed Fluorescence (TADF) green dopant
    • - Supplier difference

    Results:

    • - TADF green dopants have ion impurities
    • - There is a strong correlation between ion impurities and OLED device lifetime
    • - LT1000 can be used for screening and QC for OLED materials
    Figure4

    Figure 4 Correlation between ion impurity amounts of TADF green dopant and relative device lifetime

  3. 3. Charge injection behavior in OLED devices [4]

    Materials:

    • - OLED single layers w/wo LiF and OLED device w/wo LiF
    • - This is not a cell measurement, but a direct OLED film measurement

    Results:

    • - LiF layer reduces an electron injection barrier and increases a hole injection barrier
    • - A hole injection started a negative polarity, thus LiF contributes to the reduction of a hole injection voltage
    • - LT1000 can be used for an investigation of charge injection behaviors in OLED devices as cyclic displacement current measurement (cDCM).
    Figure5

    Figure 5 Comparison of cDCM for OLEDs with and without a Li

LT1000 PHYSICAL SPECIFICATIONS
Number of Test Channels    1
Dimension 3.4in (H) x 7.1in (W) x 14.2in (D); 8.5cm x
18cm x 36cm
Power Internal switching power supply. 100-
240VAC
Environmental Operating: 50°F to 95°F; 10°C to 35°C
(non-condensing)
   

LT1000 Technical Brief

REFERENCES

[1] Inoue M. Review of various measurement methodologies of migration ion influence on LCD image quality and new measurement proposal beyond LCD materials, J Soc Inf Disp. 2020; 28(1): 92-110.

[2] Inoue M, Oyabu N, Kumoda Y, Suenaga Y, Ishii T, Naito H. Novel measurement method of ion impurity in OPV materials. Proc of AM-FPD’19, P-14; 2019.

[3] Inoue M, Oyabu N, Kaneko Y, Kim J-Y, Yang J-H. Correlation between ion impurity in thermally activated delayed fluorescence organic light-emitting diode materials and device lifetime. DOI: 10.1002/jsid.922

[4] Inoue M, Kaneko Y, Fujimoto H, Miyazaki H, Adachi C. Evaluations of Lithium Fluoride Behavior in OLEDs by Means of Cyclic Displacement Current Measurement Method. SID Digest. 51(1), 2107-2110; 2020

CONTACT

Sales: LT1000-Sales@toyo.co.jp

Technical support: LT1000-support@toyo.co.jp