Botest Systems GmbH - Systems for lifetime and functionality testing, defect analysis and photocurrent measurements in organic light emitting diodes (OLED), organic solar cells and other applications of organic semiconductors.

TABLE OF CONTENT

01 LIV FUNCTIONALITY TEST SYSTEM

02 FUNCTIONALITY TESTING

03 AREAS OF APPLICATION

OPTIONS

Many components and features of the LIV Functionaltiy Test System can be adapted to specific customer requirements. The photodiode cover for optical measurements, sample holder with fixture and contacting pattern can be customized for different device sizes and layouts. Various additional options are available to enhance system features and benefits even more.

TEMPERATURE CONTROL

Sample heating integrated in the sample holder is available as an option. This allows measuring temperature dependence of performance parameters or accelerated testing at elevated temperature without requiring a temperature chamber. Any perturbation of running tests by changing samples or opening the temperature chamber door is excluded. With the integrated heating tests can be performed in a temperature range of 40°C to 90°C with 1°C accuracy. As an alternative to the sample heating, temperature control with Peltier elements is also available. This option is integrated in the sample holder, too, and allows running tests in a temperature range of 0°C to 90°C.

For both configurations temperature ramps are possible. Each element is controlled individually. This allows for test setups with different sample temperatures, giving greater flexibility for temperature dependent tests. The temperature control unit can be accessed via software to set and record temperature data.

LIGHT MEASUREMENT

In its standard configuration the system includes a V(λ) corrected photodiode for optical measurements. As an option TrueColor RGB sensors as used in the OLT Lifetime Test System can be used. These sensors enable monitoring voltage or lifetime dependent changes in emission color. With this option the LIV Functionality Test System offers the benefit for advanced device characterization including color-luminance-current-voltage characteristics (CLIV, CIVL or CUIL measurements).

Using the interface for external equipment luminance cameras or chroma meters can be used for optical measurements, too. Depending on camera type this option might offer a higher accuracy for luminance and color data, than can be achieved with the photodiode or color sensors. Additionally, it allows for easy calibration of the photodiode or color sensor signal by using the build-in calibration procedure in the LIV control software.

An interface for connecting a fiber optical spectrometer to the LIV sample holder is also available as an option. The spectrometer can be selected as an alternative optical sensor to run the test modes of the LIV Functionality Test System and to record voltage or lifetime dependent changesof the emission spectra. Depending on spectrometer configuration calculation of CIE color coordinates and absolute luminance from the recorded spectra is possible.

LED ILLUMINATION UNIT

For solar cell or sensor testing sun simulators are often used as external sample illumination. The benefit of having a light source with a spectral power distribution close to the solar spectrum and with an absolute irradiance close to AM1.5 is decreased by the relatively short lifetime and the resulting high cost of ownership of the simulator lamps.

For all tests requiring a stable light source, but not necessarily a solar spectrum, the ILU LED Illumination Unit is available as an option for the LIV Functionality Test System. The ILU comprises a dedicated LED control unit and a specially designed cover with high brightness LED boards. LED boards with white or with RGBW LEDs are available. Special color temperatures for white LED boards are available upon request.

Each channel of the RGBW LEDs is controlled individually, allowing color tuning and irradiance regulation. TrueColor sensors are integrated in the LED cover for continuous irradiance and color monitoring and for regulation feedback. This allows keeping the LED output constant independent of operation temperature or operation time.

The special design of the LED cover ensures relatively high uniformity over the entire illuminated area. For typical R&D OPV or organic sensor test devices with sample size of 25 x 25 mm² and cell size smaller than 10 x 10 mm² irradiance variation is below 10%. Uniformity can be further enhanced by additional diffusors that can be mounted in the LED cover. Irradiance can be varied over a wide range. The power equivalent to solar illumination can be varied from as low as 0.1 suns to almost 2 suns allowing detailed tests on irradiance dependence of performance parameters.

Control of the ILU LED Illumination Unit is integrated in the LIV Functionality Test System software. Single illumination levels as well as irradiance ramps can simply be defined during test setup.

CALIBRATION LIGHT SOURCE

For analysis and data comparison measurements with the V(λ) corrected photodiode or with TrueColor RGB sensors in the LIV Functionality Test System have to be converted to absolute luminance values. Factory calibration of the different sensors ensures linear response over the whole dynamic range and matching results of different gain levels. Conversion of the sensor measurements to absolute luminance values depends on device size, device position on the sample, device color, etc. Therefore, factors for conversion of the optical measurements to absolute luminance values cannot be obtained by factory calibration, but requires tests with customer specific device structures. Determination of conversion factors can be carried out by the customer with its real devices. This method might, however, be limited by device stability and reproducibility, especially if devices are not encapsulated.

A sample holder with LED calibration light source is available as an alternative. It can be used as optional equipment for the LIV Functionality Test System. The LED light source covers a luminance range up to 12.000 Cd/m² and has uniformity > 80 % on an active area of 40x40 mm². LED lifetime is specified > 50.000 h. These performance parameters ensure stable operation of the light source for calibration purposes.

The Botest calibration light source includes a protocol of the LED IVL characteristics measured in the final assembly. Due to the stability of the LEDs this feature enables using the calibration light source without repetitive luminance measurements. Customer specific device layouts can be optained by masking inactive areas on the LED light source. Color dependance of conversion factors can be investigated and corrected by using additional color filters. A set of RGB filters with their respective IVL characteristics are included with the calibration light source.