Browsing by Author "Mutlugun, Evren"

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Citation - WoS: 5
Citation - Scopus: 5
Cd-Free Quantum Dot Pellets for Efficient White Light Generation
(Optical Soc Amer, 2017) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, Evren
Semiconductor quantum dots have been on demand for niche optoelectronic applications providing color tenability and possessing high quantum yield and high extinction coefficient. Although the investigation of II-VI have attained a mature level of understanding of the photo physical properties, suppression of the nonradiative decay channels and enhancing the optical properties for III-V material systems still remain a challenge. In this study, we have developed and demonstrated a simple, very fast, and efficient strategy to synthesize the highly luminescent III-V group based In(Zn)P quantum dots (QDs) utilized by the effect of core growth temperature, revealing their emission kinetics and their outstanding application for white light generation. Varying the core growth temperature from 240 degrees C to 90 degrees C, limiting the extent of the precursors involved in the synthesis, and a substantial enhancement of the photoluminescence quantum yield up to 75% is demonstrated. Further modification of the synthesis procedure with optimizing the In:P precursor ratio for the first time up to 88.5 +/- 5.5% quantum yield of alloyed core/shell In(Zn)P/ZnS QDs is achieved, in which the whole synthesis process takes only around one hour. In addition, as a demonstration of Cd-free pellets, versatile pellets of green and orange emitting QDs within KCl macrocrystals are prepared. Hybridizing with blue LED, a white light with correlated color temperature of 4597K along with an unprecedentedly high color rendering index of 90 is presented. (C) 2017 Optical Society of America
Citation - WoS: 51
Citation - Scopus: 52
CdSe/ZnS Quantum Dot Films for High Performance Flexible Lighting and Display Applications
(IOP Publishing Ltd, 2016) Altintas, Yemliha; Genc, Sinan; Talpur, Mohammad Younis; Mutlugun, Evren
Colloidal quantum dots have attracted significant interest in recent years for lighting and display applications and have recently appeared in high-end market products. The integration of quantum dots with light emitting diodes has made them promising candidates for superior lighting applications with tunable optical characteristics. In this work we propose and demonstrate high quality colloidal quantum dots in their novel free-standing film forms to allow high quality white light generation to address flexible lighting and display applications. High quality quantum dots have been characterized using transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, steady state and time resolved photoluminescence and dynamic light scattering methods. The engineering of colloidal quantum dot composition and its optical properties in stand-alone film form has led to the experimentally high NTSC color gamut of 122.5 (CIE-1931) for display applications, color rendering index of 88.6, luminous efficacy of optical radiation value of 290 lm/W-opt and color temperature of 2763 K for lighting applications.
Citation - WoS: 134
Citation - Scopus: 143
Cesium-Lead Based Inorganic Perovskite Quantum-Dots as Interfacial Layer for Highly Stable Perovskite Solar Cells With Exceeding 21% Efficiency
(Elsevier, 2019) Akin, Seckin; Altintas, Yemliha; Mutlugun, Evren; Sonmezoglu, Savas
Despite the excellent photovoltaic performances of perovskite solar cells (PSCs), the instability of PSCs under severe environment (e.g. humidity, light-induced, etc.) limits further commercialization of such devices. Therefore, in recent years, research on the long-term stability improvement of PSCs has been actively carried out in perovskite field. To address these issues, we demonstrated the incorporation of ultra-thin interfacial layer of inorganic CsPbBr1.85I1.15 perovskite quantum-dots (PQDs) that can effectively passivate defects at or near to the perovskite/hole transport material (HTM) interface, significantly suppressing interfacial recombination. This passivation layer increased the open circuit voltage (V-oc) of triple-cation perovskite cells by as much as 50 mV, with champion cells achieving V-oc similar to 1.14 V. As a result, we obtained hysteresis-free cells with the efficiency beyond 21%. More importantly, devices based on such architecture are capable of resisting humidity and light-induced. Remarkably, the device employing CsPbBr1.85I1.15 demonstrated a superb shelf-stability aganist to humidity under ambient conditions (R.H. >= 40%), retaining nearly 91% of initial efficiency after 30 days, while the efficiency of control device rapidly dropped to 45% from its initial value under the same conditions. Besides benefiting from the high moisture resistivity as well as supressed ion migration, PSC5 based on PQDs showed better operational stability (retaining 94% of their initial performance) than that of the PQDs-free one under continuous light irradiation over 400 h. In addition, a faster PL decay time of 4.66 ns was attained for perovskite/PQDs structure (5.77 ns for only PQDs structure) due to the favorable energy transfer at the interface, indicating a Forster resonance energy transfer (FRET) mechanism. This work indicates that inorganic PQDs are important materials as interlayer in PSC5 to supremely enhance the device stability and efficiency.
Citation - WoS: 48
Citation - Scopus: 49
Colloidal Quantum Dot Light-Emitting Diodes Employing Phosphorescent Small Organic Molecules as Efficient Exciton Harvesters
(Amer Chemical Soc, 2014) Mutlugun, Evren; Guzelturk, Burak; Abiyasa, Agus Putu; Gao, Yuan; Sun, Xiao Wei; Demir, Hilmi Volkan
Nonradiative energy transfer (NRET) is an alternative excitation mechanism in colloidal quantum dot (QD) based electroluminescent devices (QLEDs). Here, we develop hybrid highly spectrally pure QLEDs that facilitate energy transfer pumping via NRET from a phosphorescent small organic molecule-codoped charge transport layer to the adjacent QDs. A partially codoped exciton funnelling electron transport layer is proposed and optimized for enhanced QLED performance while exhibiting very high color purity of 99%. These energy transfer pumped hybrid QLEDs demonstrate a 6-fold enhancement factor in the external quantum efficiency over the conventional QLED structure, in which energy transfer pumping is intrinsically weak.
Citation - WoS: 2
Citation - Scopus: 2
Color Enrichment Solids of Spectrally Pure Colloidal Quantum Wells for Wide Color Span in Displays
(Wiley-VCH Verlag GmbH, 2022) Erdem, Talha; Soran-Erdem, Zeliha; Isik, Furkan; Shabani, Farzan; Yazici, Ahmet Faruk; Mutlugun, Evren; Demir, Hilmi Volkan
Colloidal quantum wells (CQWs) are excellent candidates for lighting and display applications owing to their narrow emission linewidths (<30 nm). However, realizing their efficient and stable light-emitting solids remains a challenge. To address this problem, stable, efficient solids of CQWs incorporated into crystal matrices are shown. Green-emitting CdSe/CdS core/crown and red-emitting CdSe/CdS core/shell CQWs wrapped into these crystal solids are employed as proof-of-concept demonstrations of light-emitting diode (LED) integration targeting a wide color span in display backlighting. The quantum yield of the green- and red-emitting CQW-containing solids of sucrose reach approximate to 20% and approximate to 55%, respectively, while emission linewidths and peak wavelengths remain almost unaltered. Furthermore, sucrose matrix preserves approximate to 70% and approximate to 45% of the initial emission intensity of the green- and red-emitting CQWs after >60 h, respectively, which is approximate to 4x and approximate to 2x better than the drop-casted CQW films and reference (KCl) host. Color-converting LEDs of these green- and red-emitting CQWs in sucrose possess luminous efficiencies 122 and 189 lm W-elect(-1), respectively. With the liquid crystal display filters, this becomes 39 and 86 lm W-elect(-1), respectively, providing with a color gamut 25% broader than the National Television Standards Committee standard. These results prove that CQW solids enable efficient and stable color converters for display and lighting applications.
Citation - WoS: 2
Citation - Scopus: 2
Designed Optimization of Photoluminescence Emission for Carbon Dots With Bright Blue Emission at 416 NM and Mono-Exponential Decay Lifetime
(Elsevier, 2025) Ruwaih, Mohammed Abbas; Soheyli, Ehsan; Naji, Jalil; Mutlugun, Evren; Kikhavani, Tavan; Sahraei, Reza; Abbas Ruwaih, Mohammed
The presented study introduces optimized blue-emissive carbon dots (CDs) with high photoluminescence efficiency up to 65 % at 416 nm, large Stokes shift (69 nm), and full-width at half maximum (FWHM) of 73 nm. Xray photoelectron spectroscopy confirmed the formation of carbon-based bonds as the main component of CDs, with reliable amounts of O, S, and N as dopant components. These features, along with single-exponential time-decay profile at long average lifetime of 10.05 ns, supported the significant role of uniformly distributed mid-gap energy levels in the recombination process. The simplicity, low-cost, non-toxicity, and short reaction time of CDs, along with their excellent emission properties in the deep-blue region, make them suitable for use in environmental monitoring and high-contrast bioimaging.
Citation - WoS: 14
Citation - Scopus: 13
The Effect of Ligand Chain Length on the Optical Properties of Alloyed Core-Shell InPZnS/ZnS Quantum Dots
(Elsevier Science SA, 2017) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, Evren
In this work, we demonstrate the effect of organic ligands on the optical properties of alloyed core-shell InPZnS/ZnS quantum dots (QDs). We have systematically studied the synthesis and characterization of InPZnS/ZnS QDs using short and long chain length ligands i.e., butyric (C4), hexanoic (C6), octanoic (C8), dodecanoic (C12), myristic (C14), palmitic (C16) and stearic acids (C18), respectively. This study achieved more than 85% quantum yield with 43 nm full-width-half maximum value, using dodecanoic acid as the capping ligand. The properties of the QDs with short and long chain length ligands have been analyzed using UV Vis absorption spectrophotometer, steady state and time resolved photoluminescence spectrometer, X-ray diffraction, Zeta sizer, transmission electron microscopy and energy dispersive X-ray spectroscopy. (C) 2017 Published by Elsevier B.V.
Citation - WoS: 15
Citation - Scopus: 14
Effects of Silver Nanowires and Their Surface Modification on Electromagnetic Interference, Transport and Mechanical Properties of an Aerospace Grade Epoxy
(Sage Publications Ltd, 2024) Ozkutlu Demirel, Merve; Ozturkmen, Mahide B.; Savas, Muzeyyen; Mutlugun, Evren; Erdem, Talha; Oz, Yahya
The aerospace industry has progressively grown its use of composites. Electrically conductive nanocomposites are among important modern materials for this sector. We report on a bulk composite containing silver nanowires (AgNW) and an aerospace grade epoxy for use in carbon fiber reinforced polymers (CFRPs). AgNWs' surfaces were also modified to enhance their ability to be dispersed in epoxy. Composites were obtained by use of three-roll milling which is of major interest for industrial applications, especially for the aerospace sector, since the process is scalable and works for aerospace grade resins with high curing temperatures. Our main objective is to improve the electromagnetic interference (EMI) shielding performance of CFRPs via improving the properties of the resin material. The addition of AgNWs did not considerably alter the flexural strength of the epoxy, however the composite with surface-modified AgNWs has a 46 % higher flexural strength. Adding AgNWs over a low threshold concentration of 0.05 wt% significantly enhanced the electrical conductivity. Conductivities above the percolation threshold lie around 102 S/m. At a concentration of 5 wt% AgNW, the EMI shielding efficiency (SE) of epoxy increased from 3.49 to 12.31 dB. Moreover, the thermal stability of the epoxy was unaffected by AgNWs. As a result, it was discovered that (surface modified) AgNWs improved the (multifunctional) capabilities of the aerospace grade epoxy resin which might be used in CFRPs to further enhance properties of composites parts, demonstrating suitability of AgNWs' as a reinforcement material in aerospace applications.
Citation - WoS: 21
Citation - Scopus: 21
Efficient Forster Resonance Energy Transfer Donors of In(Zn)P/ZnS Quantum Dots
(Amer Chemical Soc, 2017) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, Evren
We demonstrate a detailed investigation of the effect of the type and concentration of zinc precursor on the optical properties of In(Zn)P/ZnS quantum dots. We achieved up to 87% quantum yield along with 54 nm emission bandwidth for the green emitters with changing the concentration of the Zn precursors. Employing efficient green emitters as the donor species, we demonstrated an efficient Forster resonance energy transfer (FRET) couple of green and red emitting InP-based quantum dots. With a FRET efficiency level of 70.3% achieved (analyzed from the donor lifetime with and without an acceptor), we further demonstrated the enhancement of the acceptor emission nearly twofold due to the energy transfer. Our results provide new insights toward the understanding of the excitonic interactions among donor and acceptor quantum dots of the III-V family for light harvesting applications.
Citation - WoS: 5
Citation - Scopus: 5
Electrochemical and Optical Multi-Detection of Escherichia Coli Through Magneto-Optic Nanoparticles: A Pencil-on Biosensor
(MDPI, 2024) Soysaldi, Furkan; Ekici, Derya Dincyurek; Soylu, Mehmet cagri; Mutlugun, Evren; Dincyurek Ekici, Derya
Escherichia coli (E. coli) detection suffers from slow analysis time and high costs, along with the need for specificity. While state-of-the-art electrochemical biosensors are cost-efficient and easy to implement, their sensitivity and analysis time still require improvement. In this work, we present a paper-based electrochemical biosensor utilizing magnetic core-shell Fe2O3@CdSe/ZnS quantum dots (MQDs) to achieve fast detection, low cost, and high sensitivity. Using electrochemical impedance spectroscopy (EIS) as the detection technique, the biosensor achieved a limit of detection of 2.7 x 10(2) CFU/mL for E. coli bacteria across a concentration range of 10(2)-10(8) CFU/mL, with a relative standard deviation (RSD) of 3.5781%. From an optical perspective, as E. coli concentration increased steadily from 10(4) to 10(7) CFU/mL, quantum dot fluorescence showed over 60% lifetime quenching. This hybrid biosensor thus provides rapid, highly sensitive E. coli detection with a fast analysis time of 30 min. This study, which combines the detection advantages of electrochemical and optical biosensor systems in a graphite-based paper sensor for the first time, has the potential to meet the needs of point-of-care applications. It is thought that future studies that will aim to examine the performance of the production-optimized, portable, graphite-based sensor system on real food samples, environmental samples, and especially medical clinical samples will be promising.
Citation - WoS: 59
Citation - Scopus: 63
Electroluminescence Efficiency Enhancement in Quantum Dot Light-Emitting Diodes by Embedding a Silver Nanoisland Layer
(Wiley-VCH Verlag GmbH, 2015) Yang, Xuyong; Hernandez-Martinez, Pedro Ludwig; Dang, Cuong; Mutlugun, Evren; Zhang, Kang; Demir, Hilmi Volkan; Sun, Xiao Wei
A colloidal quantum dot light-emitting diode (QLED) is reported with substantially enhanced electroluminescence by embedding a thin layer of Ag nanoislands into hole transport layer. The maximum external quantum efficiency (EQE) of 7.1% achieved in the present work is the highest efficiency value reported for green-emitting QLEDs with a similar structure, which corresponds to 46% enhancement compared with the reference device. The relevant mechanisms enabling the EQE enhancement are associated with the near-field enhancement via an effective coupling between excitons of the quantum dot emitters and localized surface plasmons around Ag nanoislands, which are found to lead to good agreement between the simulation results and the experimental data, providing us with a useful insight important for plasmonic QLEDs.
Enhanced Photoluminescence and Stability of CsPbBr3 Perovskite Nanocrystals Through AuCl Doping
(Springer, 2026) Khorasani, Azam; Mutlugun, Evren
This study delves into the transformative effects of inorganic gold chloride (AuCl) doping on all-inorganic cesium lead bromide (CsPbBr3) colloidal perovskite quantum dots (PeQDs). Using a precise hot injection synthesis method, AuCl was introduced at concentrations ranging from 0 to 10%, enabling a comprehensive analysis of its impact on the structural, morphological, and optical characteristics of CsPbBr3 PeQDs. We systematically investigated how varying AuCl levels influence photoluminescence (PL), PL quantum yield (PLQY), and the stability of these quantum dots. Advanced characterization techniques, including X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), energy dispersive X-ray analysis (EDX), Fourier-transform infrared spectroscopy (FTIR), UV-Vis absorption, steady-state PL, absolute PL measurement, and time-resolved PL (TRPL), provided a detailed insight into these changes. Our findings indicate that AuCl doping is successfully integrated into CsPbBr3 PeQDs, with 5% identified as the optimal concentration. At this level, the quantum dots show enhanced PLQY, superior crystallinity, and increased stability at 50 degrees C and in ethanol solvent compared to undoped samples. While higher doping levels reduce QY and PL slightly, they still outperform the undoped CsPbBr3 PeQDs. These results demonstrate that AuCl doping can fine-tune the structural and optical properties of CsPbBr3 PeQDs, marking a significant step forward in developing tailored materials for advanced optoelectronic applications.
Enhanced Photoluminescence via Plasmonic Gold Nanoparticles and Improved Stability of Perovskite Nanocrystals in Macroporous (Polydimethylsiloxane) PDMS Matrices
(Springer, 2025) Ocal, Sema Karabel; Tiras, Kevser Sahin; Onses, M. Serdar; Mutlugun, Evren
In this work, we report a simple and cost-effective method for improving both the environmental stability and photoluminescence quantum efficiency (PLQY) of perovskite nanocrystals (PNCs). Through their embedding in a specially designed macroporous polydimethylsiloxane (MPDMS) matrix and incorporation of plasmonic gold nanoparticles (Au NPs), remarkable improvements are achieved. The resulting MPDMS@PNC composites are seen to retain near-unity quantum efficiency even after 24-h immersion in water and are observed to retain over 85% of the original efficiency even at 75 degrees C, displaying excellent thermal stability. More interestingly, by incorporating Au NPs and subjecting the material to mechanical pressure, the lifetime of the PNCs gets further increased. This is due to the more intimate spatial arrangement of Au NPs in the porous matrix, enhancing localized surface plasmon resonance (LSPR) coupling and thereby enhancing the photoluminescence (PL) of the PNCs. In general, this approach offers a scalable and robust route to designing stable, high-performance perovskite-based materials for next-generation optoelectronic applications.
Citation - WoS: 3
Citation - Scopus: 3
Excitonic Interaction Amongst InP/ZnS Salt Pellets
(Royal Soc Chemistry, 2017) Altintas, Yemliha; Yazici, Ahmet Faruk; Unlu, Miray; Dadi, Seyma; Genc, Sinan; Mutlugun, Evren
Salt matrix has recently been introduced as a promising robust platform for embedding colloidal quantum dots to provide them with photo stability for versatile applications. This work demonstrates the excitonic interaction amongst high efficiency colloidal InP/ZnS quantum dots embedded in a KCl salt matrix. By varying the donor acceptor ratio within the solid platform, 65% Forster Resonance Energy Transfer (FRET) efficiency was attained. Optimizing the donor : acceptor ratio, we demonstrated the first FRET-enabled Cd-free pellets for white light generation possessing a color rendering index (CRI) of 84.7, correlated color temperature (CCT) of 5347.5 K, and a high luminous efficacy of optical radiation value (LER) of 324.3 lm/W-opt. Our study of excitonic interactions within quantum dot-loaded salt matrices will open new possibilities for future versatile optoelectronic applications.
Citation - WoS: 15
Citation - Scopus: 18
FRET Enabled Light Harvesting within Quantum Dot Loaded Nanofibers
(IOP Publishing Ltd, 2018) Altintas, Yemliha; Kiremitler, Nuri Burak; Genc, Sinan; Onses, M. Serdar; Mutlugun, Evren
The spatial control of the nano-emitters in novel light harvesting platforms offers great potential for the manipulation of the excitonic interaction amongst the donor-acceptor pairs of energy transferring agents. In this work, we report colloidal quantum dot loaded electrospun nanofibers as a light harvesting platform to study the excitonic interaction among them. The donor emission lifetime modified from 12.46 ns to 7.45 ns with the change in the ratio of green and red quantum dots in the nanofiber, as a result of confining acceptor quantum dots in close proximity. The spectrally narrow emitter luminescent nanofiber platforms have further been investigated for their potential of white light generation. The hybrid platform of blue LED integrated electrospun nanofibers has been shown to demonstrate a correlated color temperature of 3632.5 K, luminous efficacy of optical radiation value of 307.7 lm/W-opt along with color rendering index value of 60.
Citation - WoS: 2
Fully Inorganic Colloidal CsPbBr3 Perovskite Nanocrystals with Zn-Doping and Metal Oxide Encapsulation for Luminescent Display Panels
(Amer Chemical Soc, 2025) Khorasani, Azam; Soheyli, Ehsan; Mutlugun, Evren
Perovskite nanocrystals (PeNCs) are emerging as exceptional materials due to their high photoluminescence quantum yield, tunable bandgap, and excellent charge carrier mobility, enabling a wide range of colors and promising applications in optoelectronics and photovoltaics. Despite their advantages, PeNCs face stability challenges caused by environmental factors. In the presented study, a facile and versatile colloidal hot-injection method was used to apply the beneficial aspects of Zn-doping in cesium lead bromide (CsPbBr3) PeNCs. The uniform platelet-shaped Zn-doped CsPbBr3 PeNCs were prepared by doping with a 0.1 molar ratio of zinc-oleate solution in the perovskite precursors during synthesis. Then, zinc-oxide (ZnO) and nickel-oxide (NiO) coating layers were utilized separately to effectively reduce surface defects, encapsulate PeNCs, and improve their stability issues. To fabricate the coated PeNCs with metal oxides, zinc acetate and nickel(II) acetate tetrahydrate solutions were prepared individually and added to the crude perovskite solutions. The quantum yield of Zn-doped CsPbBr3 (CsPb1-xZnxBr3) PeNCs coated with ZnO increased from 50% for bare CsPbBr3 to over 84%, while NiO-coated PeNCs exhibited a higher yield of 90% both of which remarkably enhanced the emission stability. Moreover, NiO coatings represented a proper protection against surface imperfections and improved resistance to external stimuli. The combination of facile/effective preparation method, excellent emission efficiency, and reliable emission stability nominates the prepared colloidal composite for display pixels, detectors, and lasers.
Citation - WoS: 43
Citation - Scopus: 45
Highly Efficient Cd-Free Alloyed Core/Shell Quantum Dots With Optimized Precursor Concentrations
(Amer Chemical Soc, 2016) Altintas, Yemliha; Talpur, Mohammad Younis; Unlu, Miray; Mutlugun, Evren
The chemical composition, the emission spectral bandwidth, and photoluminescence quantum yield of a semiconductor quantum dot (QD) play an important role in the assessment of the performance of the applications related to the quantum dots. Quantum dots based on environmentally friendly compositions with high optical performance have been in demand for high-end technological applications. In this work, we propose and demonstrate a detailed synthesis approach for environmentally friendly and highly efficient InPZnS alloy/ZnS shell quantum dots. Following a systematic study of the ratio and type of the precursors involved, we achieved alloyed core shell InPZnS/ZnS QDs with tunable emission across the visible spectrum, having a record quantum efficiency up to 78% along with a full width at half-maximum as narrow as 45 nm. The effect of the systematic shell growth has been further investigated using time-resolved photoluminescence characterizations along with the observation of the suppression of the nonradiative decay channels, with the photoluminescence lifetime prolonged from 20.3 to 50.4 ns. The development of highly efficient and environmentally friendly QDs will pave the way for robust, sustainable optoelectronic applications.
Citation - WoS: 12
Citation - Scopus: 13
Highly Luminescent ZnCdTeS Nanocrystals With Wide Spectral Tunability for Efficient Color-Conversion White-Light
(IOP Publishing Ltd, 2021) Soheyli, Ehsan; Zargoush, Sirous; Yazici, Ahmet Faruk; Sahraei, Reza; Mutlugun, Evren
CdTe-based semiconductor nanocrystals (NCs) with size and composition-dependent efficient bandgap properties are historically mature nanomaterials for colloidal optoelectronic applications. In this work, we present the highly luminescent quaternary ZnCdTeS NCs with tunable emission across a wide visible spectrum from green to red spectral range. Prepared via a direct aqueous-based approach, a second capping agent of trisodium citrate (TSC) was used to enhance the photoluminescence (PL) emission efficiency, the chemical stability, and to spectrally widen the coverage of the emission spectra of ZnCdTeS NCs. Adding TCS created a remarkable blue shift from 572 nm in the absence of TSC, to 548 nm. On the other hand, upon optimization of experimental parameters, superior ZnCdTeS NCs with a narrow PL profile typically less than 50 nm, the high quantum efficiency of 76%, and tunable emission from 515-to-645 nm were synthesized in an aqueous solvent. The keynotes were the superior and reproducible luminescent properties for the core only NCs, without shell and using relatively low reaction temperatures. It was shown that in the suggested synthesis method, the high efficiency emitted color of ZnCdTeS NCs can be easily controlled from 515-to-650 nm with excellent stability against harsh conditions. The biexponential decay profiles of samples prepared at different reaction temperatures demonstrated that the average recombination lifetime is below 40 ns and increases with the growth of the ZnCdTeS NCs. Results reveal that the excitonic energy levels have the main role in the recombination process. Finally, to demonstrate the functional advantages of the prepared NCs in optoelectronics, the NCs were used to fabricate color-conversion white light-emitting diodes. The color coordinate of the device is recorded as (0.4951, 0.3647) with CRI of 91, CCT of 1954 K, and LER of 251 lm W-1 by employing only two distinct emitters for color conversion.
Citation - WoS: 88
Citation - Scopus: 85
Highly Stable, Near-Unity Efficiency Atomically Flat Semiconductor Nanocrystals of CdSe/ZnS Hetero-Nanoplatelets Enabled by ZnS-Shell Hot-Injection Growth
(Wiley-VCH Verlag GmbH, 2019) Altintas, Yemliha; Quliyeva, Ulviyya; Gungor, Kivanc; Erdem, Onur; Kelestemur, Yusuf; Mutlugun, Evren; Demir, Hilmi Volkan
Colloidal semiconductor nanoplatelets (NPLs) offer important benefits in nanocrystal optoelectronics with their unique excitonic properties. For NPLs, colloidal atomic layer deposition (c-ALD) provides the ability to produce their core/shell heterostructures. However, as c-ALD takes place at room temperature, this technique allows for only limited stability and low quantum yield. Here, highly stable, near-unity efficiency CdSe/ZnS NPLs are shown using hot-injection (HI) shell growth performed at 573 K, enabling routinely reproducible quantum yields up to 98%. These CdSe/ZnS HI-shell hetero-NPLs fully recover their initial photoluminescence (PL) intensity in solution after a heating cycle from 300 to 525 K under inert gas atmosphere, and their solid films exhibit 100% recovery of their initial PL intensity after a heating cycle up to 400 K under ambient atmosphere, by far outperforming the control group of c-ALD shell-coated CdSe/ZnS NPLs, which can sustain only 20% of their PL. In optical gain measurements, these core/HI-shell NPLs exhibit ultralow gain thresholds reaching approximate to 7 mu J cm(-2). Despite being annealed at 500 K, these ZnS-HI-shell NPLs possess low gain thresholds as small as 25 mu J cm(-2). These findings indicate that the proposed 573 K HI-shell-grown CdSe/ZnS NPLs hold great promise for extraordinarily high performance in nanocrystal optoelectronics.
Citation - WoS: 62
Citation - Scopus: 73
Improving Performance and Stability in Quantum Dot-Sensitized Solar Cell Through Single Layer Graphene/Cu2S Nanocomposite Counter Electrode
(Pergamon-Elsevier Science Ltd, 2020) Akman, Erdi; Altintas, Yemliha; Gulen, Mahir; Yilmaz, Mucahit; Mutlugun, Evren; Sonmezoglu, Savas
In this work, we presented an effective nanocomposite to modify the Cu2S film by employing single layer graphene (SLG) frameworks via chemical vapor deposition, and utilized this nanocomposite as counter electrode (CE) with CdSe/ZnS core/shell quantum dots for highly stable and efficient quantum dot-sensitized solar cell (QDSSC). Furthermore, Cu2S film is directly synthesized on SLG framework by electrodeposition method. Using this nanocomposite as CE, we have achieved the high efficiency as high as 3.93% with fill factor of 0.63, which is higher than those with bare Cu2S CE (3.40% and 0.57). This remarkable performance is attributed to the surface area enhancement by creating nanoflower-shape, the reduction of charge transfer resistance, improvement of catalytic stability, and the surface smoothness as well as good adhesion. More importantly, no visible color change and detachment from surface for the Cu2S@SLG nanocomposite was observed, demonstrating that the SLG framework is critical role in shielding the Cu2S structure from sulphur ions into electrolyte, and increasing the adhesion of the Cu2S structure on surface, thus preventing its degradation. Consequently, the Cu2S@SLG nanocomposite can be utilized as an effective agent to boost up the performance of QDSSCs. (c) 2019 Elsevier Ltd. All rights reserved.