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Towards bright and pure single photon emitters at 300 K based on GaN quantum dots on silicon
摘要： Quantum dots (QDs) based on III-nitride semiconductors are promising for single photon emission at non-cryogenic temperatures due to their large exciton binding energies. Here, we demonstrate GaN QD single photon emitters operating at 300 K with g(2)(0) = 0.17 ± 0.08. At this temperature, single photon emission rates up to 106 s?1 are reached while g(2)(0) ≤ 0.5 is maintained. Our results are achieved for GaN QDs embedded in a planar AlN layer grown on silicon, representing a promising pathway for future interlinkage with optical waveguides and cavities. These samples allow exploring the limiting factors to key performance metrics for single photon sources, such as brightness and single photon purity. While high brightness is assured by large exciton binding energies, the single photon purity is mainly affected by the spectral overlap with the biexcitonic emission. Thus, the performance of a GaN QD as a single photon emitter depends on the balance between the emission linewidth and the biexciton binding energy. Small GaN QDs with an emission energy in excess of 4.2 eV are promising candidates for future room temperature applications, since the biexciton binding energy becomes comparable to the average emission linewidth of around 55 meV.
关键词： single photon source,GaN,room temperature,wide bandgap,quantum dot
更新于2025-09-23 15:21:01
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A Novel Wide-Bandgap Small Molecule Donor for High Efficiency All-Small-Molecule Organic Solar Cells with Small Non-Radiative Energy Losses
摘要： All-small-molecule organic solar cells (SM-OSCs) have attracted considerable attention owing to the merits of small molecules, such as easy purification, well-defined chemical structure and less batch-to-batch variation. To achieve high-performance SM-OSCs, the rational design of well-matched donor and acceptor materials to reduce energy losses is extremely essential. In this work, we developed a novel wide-bandgap small molecule donor, namely BTTzR, by firstly introducing the thiazolo[5,4-d]thiazole (TTz) unit as the building block. The optimized SM-OSCs based on BTTzR and Y6 exhibited an outstanding power conversion efficiency (PCE) of 13.9%. More importantly, the devices demonstrated very small non-radiative energy losses of 0.18 eV, which are similar to that of inorganic counterparts. This work indicates that BTTzR is a promising small molecule donor material for high-performance SM-OSCs application and provides a new sight of material design to reduce the non-radiative energy losses in the OSCs.
关键词： small molecule donor,organic solar cells,energy losses,wide-bandgap,high efficiency
更新于2025-09-23 15:21:01
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Study of point defects in wide-bandgap Cu <sub/>2</sub> CdGeS <sub/>4</sub> microcrystals by temperature and laser power dependent photoluminescence spectroscopy
摘要： We present temperature and laser power dependent photoluminescence (PL) study of high quality wide-bandgap Cu2CdGeS4 microcrystals. At T = 10 K three PL bands were detected at about 1.919 eV (#1), 1.855 eV (#2) and 1.748 eV (#3). The temperature and laser power dependencies indicate that the properties of PL bands can be explained by donor- acceptor pair model, where the #1 and #2 bands result from a recombination between distant pairs involving ≈ 30 meV and different deep donor defects. The #3 PL the same shallow acceptor VCu with EA band originates from the deep donor-deep acceptor pair recombination where the depth of deep acceptor defect is more than 157 meV. Detailed analysis of the PL spectra show the absence of deep potential or band gap fluctuations in this material making it suitable for photovoltaic applications.
关键词： Cu2CdGeS4,photoluminescence,defects,wide bandgap,donor-acceptor pairs
更新于2025-09-23 15:21:01
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Potassium Induced Phase Stability Enables Stable and Efficient Widea??Bandgap Perovskite Solar Cells
摘要： The incorporation of potassium can remarkably stabilize wide-bandgap perovskites with a high Br content by the synergistic effect of the formation of 2D K2PbI4 at the grain boundaries and the interstitial occupancy in the perovskite lattices, which can effectively reduce the trap density and inhibit ion migration, thus suppressing the nonradiative recombination and photoinduced phase segregation.
关键词： phase segregation,wide-bandgap perovskite solar cells,potassium incorporation,defect passivation
更新于2025-09-23 15:21:01
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Developing Wide Bandgap Polymers with Single Benzodithiophene-Based Unit for Efficient Polymer Solar Cells
摘要： In this work, a series of solely benzodithiophene-based wide bandgap polymer donors, namely PBDTT, PBDTS, PBDTF and PBDTCl, were developed for efficient polymer solar cells (PSCs) by just varying the heteroatoms into the conjugated side chains. The effects of sulfuration, fluorination and chlorination were also investigated systematically on the overall properties of these BDT-based polymers. The HOMO levels could be lowered gradually by introducing sulfur, fluorine and chlorine atoms into the side chains, which contributed to the stepwise increased Voc (from 0.78 V to 0.84 V) in the related PSCs using Y6 as the electron acceptor. On the other hand, above side chain engineering strategy could promote the polymer chain interactions and fine-tune the phase separation of active blends, leading to the enhanced absorption, ordered molecular packing and crystallinity. Among them, the chlorinated PBDTCl exhibited not only high level absorption and crystallinity, but also the most balanced hole/electron charge transport and the most optimized morphology, giving rise to the best PCE of 13.46% with a Voc of 0.84 V, a Jsc of 23.16 mA cm-2 and an FF of 69.2 %. The chlorination strategy afforded PBDTCl synthetic simplicity but high efficiency, showing its promising photovoltaic applications for realizing low-cost practical PSCs in near future.
关键词： synthetic simplicity,benzodithiophene,sole donor unit,wide bandgap polymer donors,polymer solar cells
更新于2025-09-23 15:21:01
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A wide-bandgap nonplanar small molecule acceptor having indenofluorene core for non-fullerene polymer solar cells
摘要： Recently, the nonplanar non-fullerene acceptors (NFAs) are attractive in active layers in highly efficient polymer solar cells (PSCs) because of their up-shifted energy levels, improved absorption as well as charge transportation performances. However, presently nonplanar NFAs always absorb the lights in the long-wavelength region and even to near-infrared (NIR) region, which limits their further utilization in low-bandgap polymer donor-based PSCs. To further probe the performances of nonplanar NFAs in low-bandgap polymer-based PSCs, a new twisted NFA (i-IF-4F) having indenofluorene derivatives as the electron-donating fused-ring core was synthesized. Due to the relatively weak electron-donating ability of the indenofluorene core, this newly designed NFA has wide optical bandgap (1.79 eV) with absorption spectrum ranged from 450 to 690 nm, suitable lowest unoccupied molecular orbital (LUMO, -3.71 eV) and highest occupied molecular orbital (HOMO, -5.55 eV) energy levels, which ensure its matching well with the typically low-bandgap polymer (PTB7-Th) to achieve complementary absorption and proper differences in energy levels. After thermal annealing treatment, the film morphologies, charge transfer properties and charge recombination performances of i-IF-4F:PTB7-Th-based device was improved to a certain degree, leading to an optimized power conversion efficiency (PCE) of 6.47%. The work in this manuscript demonstrates the applicability of wide-bandgap twisted acceptors in PSCs and the possible approach to further improve the performances of wide-bandgap nonplanar acceptors in PSCs.
关键词： Polymer solar cells,Indenofluorene,Main-chain twisted small molecules,Wide bandgap non-fullerene acceptors
更新于2025-09-23 15:21:01
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High Performance Silicon Carbide Power Packaging—Past Trends, Present Practices, and Future Directions
摘要： This paper presents a vision for the future of 3D packaging and integration of silicon carbide (SiC) power modules. Several major achievements and novel architectures in SiC modules from the past and present have been highlighted. Having considered these advancements, the major technology barriers preventing SiC power devices from performing to their fullest ability were identified. 3D wire bondless approaches adopted for enhancing the performance of silicon power modules were surveyed, and their merits were assessed to serve as a vision for the future of SiC power packaging. Current efforts pursuing 3D wire bondless SiC power modules were described, and the concept for a novel SiC power module was discussed.
关键词： wide bandgap,3D packaging,high power density,power electronics,wire bondless
更新于2025-09-23 15:21:01
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Influence of precursor concentration and growth time on the surface morphology and crystallinity of α-Ga<sub>2</sub>O<sub>3</sub> thin films fabricated by mist chemical vapor deposition
摘要： Single-crystal thin films of gallium oxide (Ga2O3), an ultra-wide bandgap semiconductor, were fabricated on c-plane sapphire by mist chemical vapor deposition (mist CVD). The grown ?-Ga2O3 thin films had low surface roughness, and we characterized their initial crystal growth phase by using atomic force microscopy and X-ray diffraction. By varying the precursor concentration, we changed the surface roughness and crystallinity of the thin films. The lattice constants of the ?-Ga2O3 thin films almost matched those of the single crystal in the initial growth phase. We also found that these thin films grew hetero-epitaxially. Finally, mist CVD might have a very short incubation time in this system.
关键词： Gallium oxide,Surface morphology,Crystallinity,Precursor concentration,Mist chemical vapor deposition,Epitaxial growth,Wide bandgap semiconductors
更新于2025-09-23 15:21:01
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Synthesis and Characterization of Wide-Bandgap Conjugated Polymers Consisting of Same Electron Donor and Different Electron-Deficient Units and Their Application for Nonfullerene Polymer Solar Cells
摘要： Substantial development has been made in nonfullerene small molecule acceptors (NFSMAs) that has resulted in a significant increase in the power conversion efficiency (PCE) of nonfullerene-based polymer solar cells (PSCs). In order to achieve better compatibility with narrow-bandgap nonfullerene small molecule acceptors, it is important to design the conjugated polymers with a wide bandgap that has suitable molecular orbital energy levels. Here two donor–acceptor (D–A)-conjugated copolymers are designed and synthesized with the same thienyl-substituted benzodithiophene and different acceptors, i.e., poly{(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)-alt-(1,3-bis(2-octyldodecyl)-1,3-dihydro-2H-dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2-d]imidazol-2-one-5,8-diyl)} (DTBIA, P1) and poly{(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)-alt-(2-(5-(3-octyltridecyl)thiophen-2-yl)dithieno[3′,2′:3,4;2″,3″:5,6]benzo[1,2-d]thiazole-5,8-diyl)} (TDTBTA, P2) (and their optical and electrochemical properties are investigated). Both P1 and P2 exhibit similar deeper highest occupied molecular orbital energy level and different lowest unoccupied molecular orbital energy level. Both the copolymers have complementary absorption with a well-known nonfullerene acceptor ITIC-F. When blended with a narrow-bandgap acceptor ITIC-F, the PSCs based on P1 show a power conversion efficiency of 11.18% with a large open-circuit voltage of 0.96 V, a Jsc of 16.89 mA cm?2, and a fill factor (FF) of 0.69, which is larger than that for P2 counterpart (PCE = 9.32%, Jsc = 15.88 mA cm?2, Voc = 0.91 V, and FF = 0.645). Moreover, the energy losses for the PSCs based on P1 and P2 are 0.54 and 0.59 eV, respectively. Compared to P2, the P1-based PSCs show high values of incident photon to current conversion efficiency (IPCE) in the shorter-wavelength region (absorption of donor copolymer), more balanced hole and electron mobilities, and favorable phase separation with compact π–π stacking distance.
关键词： solvent vapor annealing,polymer solar cells,nonfullerene acceptors,wide-bandgap polymers
更新于2025-09-23 15:19:57
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Largea??Scale Ultrathin 2D Widea??Bandgap BiOBr Nanoflakes for Gatea??Controlled Deepa??Ultraviolet Phototransistors
摘要： Ternary two-dimensional (2D) semiconductors with controllable wide bandgap, high ultraviolet (UV) absorption coefficient, and critical tuning freedom degree of stoichiometry variation have a great application prospect for UV detection. However, as-reported ternary 2D semiconductors often possess a bandgap below 3.0 eV, which must be further enlarged to achieve comprehensively improved UV, especially deep-UV (DUV), detection capacity. Herein, sub-one-unit-cell 2D monolayer BiOBr nanoflakes (≈0.57 nm) with a large size of 70 μm are synthesized for high-performance DUV detection due to the large bandgap of 3.69 eV. Phototransistors based on the 2D ultrathin BiOBr nanoflakes deliver remarkable DUV detection performance including ultrahigh photoresponsivity (Rλ, 12739.13 A W?1), ultrahigh external quantum efficiency (EQE, 6.46 × 106%), and excellent detectivity (D*, 8.37 × 1012 Jones) at 245 nm with a gate voltage (Vg) of 35 V attributed to the photogating effects. The ultrafast response (τrise = 102 μs) can be achieved by utilizing photoconduction effects at Vg of ?40 V. The combination of photocurrent generation mechanisms for BiOBr-based phototransistors controlled by Vg can pave a way for designing novel 2D optoelectronic materials to achieve optimal device performance.
关键词： monolayer BiOBr,deep UV phototransistors,wide-bandgap semiconductors,high gain
更新于2025-09-23 15:19:57