Abstract
We demonstrate the application of the CELIV (charge carrier extraction by linearly increasing voltage) technique to bilayer organic light-emitting devices (OLEDs) in order to selectively determine the hole mobility in N,N0-bis(1-naphthyl)-N,N0-diphenyl-1,10-biphenyl-4,40-diamine (α-NPD). In the CELIV technique, mobile charges in the active layer are extracted by applying a negative voltage ramp, leading to a peak superimposed to the measured displacement current whose temporal position is related to the charge carrier mobility. In fully operating devices, however, bipolar carrier transport and recombination complicate the analysis of CELIV transients as well as the assignment of the extracted mobility value to one charge carrier species. This has motivated a new approach of fabricating dedicated metal-insulator-semiconductor (MIS) devices, where the extraction current contains signatures of only one charge carrier type. In this work, we show that the MIS-CELIV concept can be employed in bilayer polar OLEDs as well, which are easy to fabricate using most common electron transport layers (ETLs), like Tris-(8-hydroxyquinoline)aluminum (Alq3). Due to the macroscopic polarization of the ETL, holes are already injected into the hole transport layer below the built-in voltage and accumulate at the internal interface with the ETL. This way, by a standard CELIV experiment only holes will be extracted, allowing us to determine their mobility. The approach can be established as a powerful way of selectively measuring charge mobilities in new materials in a standard device configuration.
Highlights
Charge carrier mobility is one of the most important material parameters in organic electronics
We demonstrate the application of the charge extraction by linearly increasing voltage (CELIV) technique to bilayer organic light-emitting devices (OLEDs) in order to selectively determine the hole mobility in N,N0-bis(1-naphthyl)-N,N0-diphenyl-1,10-biphenyl-4,40-diamine (a-NPD)
In the CELIV technique, mobile charges in the active layer are extracted by applying a negative voltage ramp, leading to a peak superimposed to the measured displacement current whose temporal position is related to the charge carrier mobility
Summary
Charge carrier mobility is one of the most important material parameters in organic electronics. In organic lightemitting diodes (OLEDs) where electrons and holes are injected by electrodes and recombine in the active layer, leading to light emission, one of the key factors determining the (current-to-luminance) efficiency is the charge balance factor.1–3 This factor can be maximized by the stack design, e.g., using blocking layers, as well as optimizing the carrier mobilities in the charge transport layers. The charge carrier mobility of the majority charge carriers in an organic semiconductor material is one of the most relevant parameters for further optimization of organic electronic devices Various experimental techniques such as space-charge limited current-voltage curves, timeof-flight, admittance spectroscopy, dark injection transients, field-effect mobility, and charge extraction by linearly increasing voltage (CELIV) are in principle available to assess this parameter. The only one that can be performed on fully operating devices is photo-CELIV in organic solar cells, where the identification of the sign of the majority charge carrier is a non-obvious task,
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
