@article{salehi_ho_chen_peng_yersin_so_2017, title={Highly Efficient Organic Light-Emitting Diode Using A Low Refractive Index Electron Transport Layer}, volume={5}, ISSN={["2195-1071"]}, DOI={10.1002/adom.201700197}, abstractNote={A low refractive index electron transport layer (ETL) can be very effective in enhancing the out‐coupling efficiency of an organic light‐emitting diode (OLED). However, most organic films show a refractive index close to 1.8. In this work, it has been discovered that tris‐[3‐(3‐pyridyl)mesityl]borane (3TPYMB) has a low refractive index of 1.65 (at 550 nm), which is the lowest refractive index ETL among the commonly used ETLs up to date. Using 3TPYMB as an ETL, a solution processed OLED is demonstrated with nearly a 76% enhancement in external quantum efficiency (EQE). Optical simulation results of this study show that 59% of the enhancement comes from the low refractive index 3TPYMB, and the remaining 17% from the change in charge balance due to the 3TPYMB ETL in the OLED devices.}, number={11}, journal={ADVANCED OPTICAL MATERIALS}, author={Salehi, Amin and Ho, Szuheng and Chen, Ying and Peng, Cheng and Yersin, Hartmut and So, Franky}, year={2017}, month={Jun} }
 @article{peng_salehi_chen_danz_liaptsis_so_2017, title={Probing the Emission Zone Length in Organic Light Emitting Diodes via Photoluminescence and Electroluminescence Degradation Analysis}, volume={9}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.7b13537}, abstractNote={The understanding and control of the emission zone in organic light emitting diodes (OLEDs) is crucial to the device operational stability. Using the photoluminescence and electroluminescence degradation data, we have developed a modeling methodology to quantitatively determine the length of the emission zone and correlate that with the degradation mechanism. We first validate the modeling results by studying the emitter concentration effect on operational stability of devices using the well-studied thermal activated delayed fluorescent (TADF) emitter (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN), and our results are consistent with previous published data. We further applied this methodology to study the emitter concentration effect using another TADF emitter, 4-carbazolyl-2-methylisoindole-1,3-dione (dopant 1). The results show that the emission zone of the dopant 1 devices is narrower than the 4CzIPN device, leading to faster degradation. While a higher emitter concentration does not result in widening of the emission zone, we were able to widen the emission zone and hence extend the device lifetime using a mixed host.}, number={47}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Peng, Cheng and Salehi, Amin and Chen, Ying and Danz, Michael and Liaptsis, Georgios and So, Franky}, year={2017}, month={Nov}, pages={41421–41427} }
 @article{peng_liu_fu_pan_chen_so_schanze_2016, title={Corrugated Organic Light Emitting Diodes Using Low T-g Electron Transporting Materials}, volume={8}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.6b02669}, abstractNote={A corrugated organic light emitting diode (OLED) with enhanced light extraction is realized by incorporating a corrugated composite electron transport layer (ETL) consisting of two ETLs with different glass transition temperatures. The morphology of the corrugated structure is characterized with atomic force microscopy. The results show that the corrugation can be controlled by the layer thicknesses and annealing temperature. Compared with the control planar device, the corrugated OLED shows a more than 35% enhancement in current efficiency from 31 cd/A to 43 cd/A and a 20% enhancement in external quantum efficiency from 10% to 12% at 100 cd/m(2). In addition, the corrugated OLED also has a greatly improved operational stability. The LT90 lifetime of a device operated at 1000 cd/m(2) is improved greater than 100-fold in the corrugated OLED.}, number={25}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Peng, Cheng and Liu, Shuyi and Fu, Xiangyu and Pan, Zhenxing and Chen, Ying and So, Franky and Schanze, Kirk S.}, year={2016}, month={Jun}, pages={16192–16199} }
 @article{liu_peng_cruz_chen_so_2016, title={Degradation study of organic light-emitting diodes with solution-processed small molecule phosphorescent emitting layers}, volume={4}, ISSN={["2050-7534"]}, DOI={10.1039/c6tc02962k}, abstractNote={The degradation mechanisms of solution processed small molecule phosphorescent OLEDs are investigated along with thermal evaporated devices. Hole-induced degradation in the presence of excited states is found to be a major culprit for the fast degradation in solution-processed devices. Degradation in the solution-processed emitting layer (EML) is found to be strongly dependent on the initial hole injection/transport properties of the EML. Gas chromatography-mass spectrometry (GC-MS) studies on solvents used to prepare the solution-processed EMLs reveal that solvent impurities are the dominant reason for their substantially shorter operational lifetime compared with thermal evaporated devices.}, number={37}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, author={Liu, Shuyi and Peng, Cheng and Cruz, Alexandria and Chen, Ying and So, Franky}, year={2016}, month={Oct}, pages={8696–8703} }
 @article{ho_chen_liu_peng_zhao_so_2016, title={Interface Effect on Efficiency Loss in Organic Light Emitting Diodes with Solution Processed Emitting Layers}, volume={3}, ISSN={["2196-7350"]}, DOI={10.1002/admi.201600320}, abstractNote={The performance of multilayered OLEDs with a solution processed emitting layer (EML) is compared to that of counterparts with an evaporated EML and it is found that the interfacial energy changes at the EML and electron transport layer (ETL) interface is a key factor determining the device efficiency. From the results of exciplex photoluminescence emission at the EML/ETL interface and energetic disorder measurements, it is revealed that there is an energy shift in the solution processed EML along with a band tail broadening compared with the device with an evaporated EML, resulting in inefficient hole blocking at the EML/ETL interface and a decrease in device efficiency. Using an ETL with a deep highest occupied molecular orbital (HOMO) level can ameliorate this problem, resulting in a solution processed OLED with a high external quantum efficiency of 29%.}, number={19}, journal={ADVANCED MATERIALS INTERFACES}, author={Ho, Szuheng and Chen, Ying and Liu, Shuyi and Peng, Cheng and Zhao, Dewei and So, Franky}, year={2016}, month={Oct} }