@article{dong_fu_seyitliyev_darabi_mendes_lei_chen_chang_amassian_gundogdu_et al._2022, title={Cavity Engineering of Perovskite Distributed Feedback Lasers}, volume={9}, ISSN={2330-4022 2330-4022}, url={http://dx.doi.org/10.1021/acsphotonics.2c00917}, DOI={10.1021/acsphotonics.2c00917}, abstractNote={Perovskite distributed feedback (DFB) lasers are gaining increasing attention due to their solution processability, band gap tunability, single-mode operation, and low threshold. However, it is still challenging to fabricate high-quality DFB cavities on perovskite films, resulting in a mismatch between the optical resonance and the gain spectrum. To address these issues, here we develop a systematic facile approach to fabricate and design the cavities of perovskite surface-emitting DFB lasers. Using this approach, the cavity fabrication is simplified by adding polyvinylpyrrolidone into the perovskite precursor solutions, enabling a simple nanoimprint on perovskite films, while the cavity engineering is guided by a systematic optical mode analysis and conducted through simply varying the solution concentration to manipulate the effective index of the waveguide mode. With this methodology, we fabricated perovskite DBF lasers with an optimized optical resonance, whereby a low threshold of 20 μJ cm–2 was achieved. Our approach provides an effective way to fabricate high-performance perovskite DFB lasers. With this technique, we can easily realize high-precision cavity tuning with a precision of better than 5 nm.}, number={9}, journal={ACS Photonics}, publisher={American Chemical Society (ACS)}, author={Dong, Qi and Fu, Xiangyu and Seyitliyev, Dovletgeldi and Darabi, Kasra and Mendes, Juliana and Lei, Lei and Chen, Yi-An and Chang, Chih-Hao and Amassian, Aram and Gundogdu, Kenan and et al.}, year={2022}, month={Aug}, pages={3124–3133} }
 @article{biliroglu_findik_mendes_seyitliyev_lei_dong_mehta_temnov_so_gundogdu_2022, title={Room-temperature superfluorescence in hybrid perovskites and its origins}, volume={16}, ISSN={["1749-4893"]}, url={https://doi.org/10.1038/s41566-022-00974-4}, DOI={10.1038/s41566-022-00974-4}, number={4}, journal={NATURE PHOTONICS}, publisher={Springer Science and Business Media LLC}, author={Biliroglu, Melike and Findik, Gamze and Mendes, Juliana and Seyitliyev, Dovletgeldi and Lei, Lei and Dong, Qi and Mehta, Yash and Temnov, Vasily V. and So, Franky and Gundogdu, Kenan}, year={2022}, month={Apr}, pages={324-+} }
 @article{fu_mehta_chen_lei_zhu_barange_dong_yin_mendes_he_et al._2021, title={Directional Polarized Light Emission from Thin‐Film Light‐Emitting Diodes}, volume={33}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202006801}, DOI={10.1002/adma.202006801}, abstractNote={Abstract Light‐emitting diodes (LEDs) with directional and polarized light emission have many photonic applications, and beam shaping of these devices is fundamentally challenging because they are Lambertian light sources. In this work, using organic and perovskite LEDs (PeLEDs) for demonstrations, by selectively diffracting the transverse electric (TE) waveguide mode while suppressing other optical modes in a nanostructured LED, the authors first demonstrate highly directional light emission from a full‐area organic LED with a small divergence angle less than 3° and a TE to transverse magnetic (TM) polarization extinction ratio of 13. The highly selective diffraction of only the TE waveguide mode is possible due to the planarization of the device stack by thermal evaporation and solution processing. Using this strategy, directional and polarized emission from a perovskite LED having a current efficiency 2.6 times compared to the reference planar device is further demonstrated. This large enhancement in efficiency in the PeLED is attributed to a larger contribution from the TE waveguide mode resulting from the high refractive index in perovskite materials.}, number={9}, journal={Advanced Materials}, publisher={Wiley}, author={Fu, Xiangyu and Mehta, Yash and Chen, Yi‐An and Lei, Lei and Zhu, Liping and Barange, Nilesh and Dong, Qi and Yin, Shichen and Mendes, Juliana and He, Siliang and et al.}, year={2021}, month={Jan}, pages={2006801} }
 @article{findik_biliroglu_seyitliyev_mendes_barrette_ardekani_lei_dong_so_gundogdu_2021, title={High-temperature superfluorescence in methyl ammonium lead iodide}, volume={15}, ISSN={1749-4885 1749-4893}, url={http://dx.doi.org/10.1038/s41566-021-00830-x}, DOI={10.1038/s41566-021-00830-x}, abstractNote={Light–matter interactions can create and manipulate collective many-body phases in solids1–3, which are promising for the realization of emerging quantum applications. However, in most cases, these collective quantum states are fragile, with a short decoherence and dephasing time, limiting their existence to precision tailored structures under delicate conditions such as cryogenic temperatures and/or high magnetic fields. In this work, we discovered that the archetypal hybrid perovskite, MAPbI3 thin film, exhibits such a collective coherent quantum many-body phase, namely superfluorescence, at 78 K and above. Pulsed laser excitation first creates a population of high-energy electron–hole pairs, which quickly relax to lower energy domains and then develop a macroscopic quantum coherence through spontaneous synchronization. The excitation fluence dependence of the spectroscopic features and the population kinetics in such films unambiguously confirm all the well-known characteristics of superfluorescence. These results show that the creation and manipulation of collective coherent states in hybrid perovskites can be used as the basic building blocks for quantum applications4,5. A collective coherent quantum many-body phase, namely superfluorescence, is observed in CH3NH3PbI3 at 78 K. The excitation fluence dependence of the spectroscopic features and the population kinetics confirm all its well-known characteristics.}, number={9}, journal={Nature Photonics}, publisher={Springer Science and Business Media LLC}, author={Findik, Gamze and Biliroglu, Melike and Seyitliyev, Dovletgeldi and Mendes, Juliana and Barrette, Andrew and Ardekani, Hossein and Lei, Lei and Dong, Qi and So, Franky and Gundogdu, Kenan}, year={2021}, month={Jun}, pages={676–680} }
 @article{lei_seyitliyev_stuard_mendes_dong_fu_chen_he_yi_zhu_et al._2020, title={Efficient Energy Funneling in Quasi-2D Perovskites: From Light Emission to Lasing}, volume={32}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201906571}, abstractNote={Quasi-2D Ruddlesden-Popper halide perovskites with a large exciton binding energy, self-assembled quantum wells, and high quantum yield draw attention for optoelectronic device applications. Thin films of these quasi-2D perovskites consist of a mixture of domains having different dimensionality, allowing energy funneling from lower-dimensional nanosheets (high-bandgap domains) to 3D nanocrystals (low-bandgap domains). High-quality quasi-2D perovskite (PEA)2 (FA)3 Pb4 Br13 films are fabricated by solution engineering. Grazing-incidence wide-angle X-ray scattering measurements are conducted to study the crystal orientation, and transient absorption spectroscopy measurements are conducted to study the charge-carrier dynamics. These data show that highly oriented 2D crystal films have a faster energy transfer from the high-bandgap domains to the low-bandgap domains (<0.5 ps) compared to the randomly oriented films. High-performance light-emitting diodes can be realized with these highly oriented 2D films. Finally, amplified spontaneous emission with a low threshold 4.16 µJ cm-2 is achieved and distributed feedback lasers are also demonstrated. These results show that it is important to control the morphology of the quasi-2D films to achieve efficient energy transfer, which is a critical requirement for light-emitting devices.}, number={16}, journal={ADVANCED MATERIALS}, author={Lei, Lei and Seyitliyev, Dovletgeldi and Stuard, Samuel and Mendes, Juliana and Dong, Qi and Fu, Xiangyu and Chen, Yi-An and He, Siliang and Yi, Xueping and Zhu, Liping and et al.}, year={2020}, month={Apr} }
 @misc{dong_lei_mendes_so_2020, title={Operational stability of perovskite light emitting diodes}, volume={3}, ISSN={["2515-7639"]}, DOI={10.1088/2515-7639/ab60c4}, abstractNote={Abstract Organometal halide perovskite light emitting diodes (LEDs) have attracted a lot of attention in recent years, owing to the rapid progress in device efficiency. However, their short operational lifetime severely impedes the practical uses of these devices. The operating stability of perovskite LEDs are due to degradation due to ambient environment and degradation during operation. The former can be suppressed by encapsulation while the latter one is the intrinsic degradation due to the electrochemical stability of the perovskite materials. In addition, perovskites also suffer from ion migration which is a major degradation mechanism in perovskite LEDs. In this review, we specifically focus on the operational stability of perovskite LEDs. The review is divided into two parts: the first part contains a summary of various degradation mechanisms and some insight on the degradation behavior and the second part is the strategies how to improve the operational stability, especially the strategies to suppress ion migration. Based on the current advances in the literature, we finally present our perspectives to improve the device stability.}, number={1}, journal={JOURNAL OF PHYSICS-MATERIALS}, author={Dong, Qi and Lei, Lei and Mendes, Juliana and So, Franky}, year={2020}, month={Jan} }
 @article{dong_mendes_lei_seyitliyev_zhu_he_gundogdu_so_2020, title={Understanding the Role of Ion Migration in the Operation of Perovskite Light-Emitting Diodes by Transient Measurements}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c14269}, abstractNote={Perovskite light-emitting diodes have been gaining attention in recent years due to their high efficiencies. Despite of the recent progress made in device efficiency, the operation mechanisms of these devices are still not well understood, especially the effects of ion migration. In this work, the role of ion migration is investigated by measuring the transient electroluminescence and current responses, with both the current and efficiency showing a slow response in a time scale of tens of milliseconds. The results of the charge injection dynamics show that the slow response of the current is attributed to the migration and accumulation of halide ions at the anode interface, facilitating hole injection and leading to a strong charge imbalance. Further, the results of the charge recombination dynamics show that the slow response of the efficiency is attributed to enhanced charge injection facilitated by ion migration, which leads to an increased carrier density favoring bimolecular radiative recombination. Through a combined analysis of both charge injection and recombination dynamics, we finally present a comprehensive picture of the role of ion migration in device operation.}, number={43}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Dong, Qi and Mendes, Juliana and Lei, Lei and Seyitliyev, Dovletgeldi and Zhu, Liping and He, Siliang and Gundogdu, Kenan and So, Franky}, year={2020}, month={Oct}, pages={48845–48853} }
 @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 OLEDs suffer from viewing angle dependent spectral shift due to microcavity effects. To address this issue, we introduce a novel top‐emitting OLED with a dielectric spacer that forms multiple cavity modes. The resulting device shows almost no color shift at different viewing angles.}, 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} }