| TEST EXAMPLES |
PERFORMANCE UNIFORMITY OF LARGE AREA OLEDsThe PCT Photoelectric Test System is used for studying spatial variations in performance of large area OLEDs. While light emission is very uniform, current mapping shows some non-uniformities. At forward bias the observed features can be attributed to effects caused by resistance variations. At reverse bias the current map shows completely different features. These can be linked to effects in substrate pretreatment that are sometimes observed during manufacturing. The results show that the photoelectric properties are very sensitive to differences in device properties. Effects not observed in light emission can be detected with this method. This allows for using the PCT for early detection of performance variations and for quality and process control. |
STUDY OF SHORTS IN OLEDsThe PCT Photoelectric Test System can be used for defect analysis in different applications of organic semiconductors. Here it is applied to large area OLEDs with shorts. The analysis of photocurrent maps yields valuable information on the origin of these defects. Effects of cathode distruction, e.g. by high reverse bias, can be identified and the origin of the short can be localized. Different types of shorts can be distinguished. For shorts forming along metal buslines significant material damage due to heat generation at the short is observed. Furthermore, an increase of the photoresponse at the edge of such defects is measured. While any technique requiring light emission is limited in use for OLEDs with shorts, current mapping can still be used for defect analysis. By applying a bias voltage the PCT can even be used for studying the evolution of shorts. |
DEGRADATION OF ORGANIC SOLAR CELLS
Only for OLEDs defects can be easily observed in light emission. For all other organic semiconductor devices defects and local performance variations can hardly be measured. In organic solar cells for example a decrease of device performance can either be caused by degradation of the bulk active material or by local device degradation. Using the current mapping mode of the PCT it is possible to distinguish these two effects. In the measurements carried out the performance decrease of the measured organic solar cells could be attributed to local device degradation. In more detailed studies local IV characteristics of different areas of the device were recorded. All three characteristic parameters - Isc, Uoc, and Ubi – show similar behavior. Thus, the local degradation is caused by electrode corrosion due to insufficent encapsulation. The results prove that for non-emitting organic semiconductor devices too the PCT Photoelectric Test System is a versatile tool for visualization of defects and for the comprehensive analysis of device performance. |
FUNCTIONALITY TESTING OF LARGE AREA ORGANIC SENSOR ARRAYS
The PCT Photoelectric Test System is used for functionality tests of a large area sensor array. Device size is larger than 150 x 150 mm² with individual sensors of approx. 500 µm diameter. Optical inspection can only be used to check macroscopic coating uniformity and to find obvious coating defects. In contrast, photocurrent mapping with the PCT allows for testing the functionality of each sensor. Defective sensors can be identified easily. Thus, the PCT is very well suited for quality control of the large area sensor array. Furthermore, detailed analysis of the photoresponse of each sensor is used to investigate on local performance variations within a sensor. These findings can be correlated to the coating process and can be used to optimize the manufacturing process. |
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