@article{amoah_fu_yin_dong_dong_so_2022, title={Curved Mirror Arrays for Light Extraction in Top-Emitting Organic Light-Emitting Diodes}, volume={2}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.1c21128}, abstractNote={The light outcoupling efficiency of a top-emitting organic light-emitting diode (OLED) is only about 20%, and the majority of the light is trapped in the waveguide modes and surface plasmon polariton (SPP) modes. Extracting the trapped modes can reduce the device power consumption and improve the operating lifetime. In this study, we demonstrate a top-emitting OLED structure with a dielectric spacer to suppress the SPP mode and with a patterned back mirror to extract the waveguide modes. We examine and compare several curved mirror arrays and conclude that a micromirror array (μMA) can efficiently extract the waveguide modes while minimizing the absorption loss. The optimized μMA device with a semi-transparent top electrode shows a 36% external quantum efficiency, 2 times higher than the referenced device. This optical design can be easily incorporated into a top-emitting device and has a great potential for displays and lighting applications.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Amoah, Stephen and Fu, Xiangyu and Yin, Shichen and Dong, Qi and Dong, Chen and So, Franky}, year={2022}, month={Feb}, pages={9377–9385} }
 @article{dong_fu_cao_amoah_gundogdu_li_so_2020, title={Multi-mode Organic Light-Emitting Diode to Suppress the Viewing Angle Dependence}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c05825}, abstractNote={A typical top emitting OLED has a strong microcavity effect because of the two reflective electrodes. The cavity effect causes a serious color shift with the viewing angles and restricts the organic layer thickness. To overcome these drawbacks, we designed a multi-mode OLED structure having dual-dielectric spacer layers, which extend the cavity length by more than 10 times. This design completely eliminates the intrinsic cavity effect caused by the top and bottom boundaries respectively and provides freedom for the organic layer thickness. We demonstrate these effects in a white multi-mode OLED using a white emitter, which shows a negligible angular chromaticity shift of 0.006 from 0° to 70° and a Lambertian emission profile. The simple design and the perfect angular color profiles make the multi-mode OLED structure promising in large-area displays and solid-state lighting applications.}, number={28}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Dong, Chen and Fu, Xiangyu and Cao, Linyu and Amoah, Stephen and Gundogdu, Kenan and Li, Jian and So, Franky}, year={2020}, month={Jul}, pages={31667–31676} }
 @article{fu_chen_shin_mehta_chen_barange_zhu_amoah_chang_so_2020, title={Recovering cavity effects in corrugated organic light emitting diodes}, volume={28}, ISSN={["1094-4087"]}, DOI={10.1364/OE.404412}, abstractNote={Cavity effects play an important role in determining the out-coupling efficiency of an OLED. By fabricating OLEDs on corrugated substrates, the waveguide and SPP modes can be extracted by diffraction. However, corrugation does not always lead to an enhancement in out-coupling efficiency due to the reduction of the electrode reflectance and hence the cavity effects. Based on the results of our rigorous couple-wave analysis (RCWA) simulation, we found that the cavity effects can be partially recovered using a low index Teflon layer inserted between the ITO anode and the substrate due to the enhancement of the reflectance of the corrugated electrodes. To verify the simulation results, we fabricated corrugated OLEDs having a low-index Teflon interlayer with an EQE of 36%, which is 29% higher than an optimized planar OLED. By experimentally measuring the OLED air mode dispersion, we confirm the cavity emission of a corrugated OLED is enhanced by the low index layer.}, number={21}, journal={OPTICS EXPRESS}, author={Fu, Xiangyu and Chen, Yi-An and Shin, Dong-Hun and Mehta, Yash and Chen, I-Te and Barange, Nilesh and Zhu, Liping and Amoah, Stephen and Chang, Chih-Hao and So, Franky}, year={2020}, month={Oct}, pages={32214–32225} }
 @article{dong_fu_amoah_rozelle_shin_salehi_mendes_so_2019, title={Eliminate angular color shift in top-emitting OLEDs through cavity design}, volume={27}, ISSN={["1938-3657"]}, DOI={10.1002/jsid.792}, abstractNote={Abstract}, number={8}, journal={JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY}, author={Dong, Chen and Fu, Xiangyu and Amoah, Stephen and Rozelle, Adam and Shin, Dong-Hun and Salehi, Amin and Mendes, Juliana and So, Franky}, year={2019}, month={Aug}, pages={469–479} }
 @article{straka_amoah_schwartz_2017, title={Densification of thoria through flash sintering}, volume={7}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2017.70}, abstractNote={Thorium dioxide (thoria, ThO_2) is used in refractory applications and as nuclear fuel. Its melting temperature, the highest of any binary oxide, makes it a difficult system to process. Here we report on the effects of flash sintering on the densification of thoria. We found 95% of theoretical density is obtained at ~950 °C (~30% of the melting temperature) with an electric field of 800 V/cm. Variation in power density had a minimal effect on the densification. Scanning electron microscopy images show the effects of flash sintering on grain size as a function of electric field.}, number={3}, journal={MRS COMMUNICATIONS}, author={Straka, W. and Amoah, S. and Schwartz, J.}, year={2017}, month={Sep}, pages={677–682} }