| 1. |
- Alharbi, Essa A., et al.
(författare)
-
Formation of High-Performance Multi-Cation Halide Perovskites Photovoltaics by delta-CsPbI3/delta-RbPbI3 Seed-Assisted Heterogeneous Nucleation
- 2021
-
Ingår i: Advanced Energy Materials. - : John Wiley & Sons. - 1614-6832 .- 1614-6840. ; 11:16
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of perovskite solar cells is highly dependent on the fabrication method; thus, controlling the growth mechanism of perovskite crystals is a promising way towards increasing their efficiency and stability. Herein, a multi-cation halide composition of perovskite solar cells is engineered via the two-step sequential deposition method. Strikingly, it is found that adding mixtures of 1D polymorphs of orthorhombic delta-RbPbI3 and delta-CsPbI3 to the PbI2 precursor solution induces the formation of porous mesostructured hexagonal films. This porosity greatly facilitates the heterogeneous nucleation and the penetration of FA (formamidinium)/MA (methylammonium) cations within the PbI2 film. Thus, the subsequent conversion of PbI2 into the desired multication cubic alpha-structure by exposing it to a solution of formamidinium methylammonium halides is greatly enhanced. During the conversion step, the delta-CsPbI3 also is fully integrated into the 3D mixed cation perovskite lattice, which exhibits high crystallinity and superior optoelectronic properties. The champion device shows a power conversion efficiency (PCE) over 22%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining more than 90% of its initial value of PCE under 1 Sun illumination with maximum power point tracking for 400 h.
|
|
| 2. |
- Butte, Raphael, et al.
(författare)
-
Optical absorption edge broadening in thick InGaN layers : Random alloy atomic disorder and growth mode induced fluctuations
- 2018
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 112:3
-
Tidskriftsartikel (refereegranskat)abstract
- To assess the impact of random alloying on the optical properties of the InGaN alloy, high-quality InxGa1-xN (0 < x < 0.18) epilayers grown on c-plane free-standing GaN substrates are characterized both structurally and optically. The thickness (25-100 nm) was adjusted to keep these layers pseudomorphically strained over the whole range of explored indium content as checked by x-ray diffraction measurements. The evolution of the low temperature optical absorption (OA) edge line-width as a function of absorption energy, and hence the indium content, is analyzed in the framework of the random alloy model. The latter shows that the OA edge linewidth should not markedly increase above an indium content of 4%, varying from 17 meV to 30 meV for 20% indium. The experimental data initially follow the same trend with, however, a deviation from this model for indium contents exceeding only similar to 2%. Complementary room temperature near-field photoluminescence measurements carried out using a scanning near-field optical microscope combined with simultaneous surface morphology mappings reveal spatial disorder due to growth meandering. We conclude that for thick high-quality pseudomorphic InGaN layers, a deviation from pure random alloying occurs due to the interplay between indium incorporation and longer range fluctuations induced by the InGaN step-meandering growth mode.
|
|
| 3. |
- De Luca, Eleonora, et al.
(författare)
-
Modal phase matching in nanostructured zinc-blende semiconductors for second-order nonlinear optical interactions
- 2017
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 96:7
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate enhanced second-harmonic generation in arrays of nanowaveguides satisfying modal-phase-matching condition, both theoretically and experimentally. The overlap of interacting fields defined by the fundamental mode of the pump and the second-order mode of the second-harmonic wave is enhanced by the longitudinal component of the nonlinear polarization density. For guided modes with significant longitudinal electric field components, the overlap of fields is comparable to that obtained in the quasi-phase-matching technique leading to higher conversion efficiencies. Thus, the presented method is preferable to achieve higher conversion efficiency in second-order nonlinear processes in nanowaveguides.
|
|
| 4. |
- De Luca, Eleonora, et al.
(författare)
-
Modal phase matching in nanostructured zincblende semiconductors for second-harmonic generation
- 2017
-
Ingår i: Optics InfoBase Conference Papers. - : OSA - The Optical Society. - 9781943580279
-
Konferensbidrag (refereegranskat)abstract
- Gallium phosphide nanowaveguide arrays, designed to fulfill the phase matching conditions and field-overlap, are characterized by second-harmonic generation. The bandwidth of 30nm with maximum conversion efficiency of 10-3 is measured for 150fs optical pulses.
|
|
| 5. |
- Ivanov, Ruslan, et al.
(författare)
-
Polarization-Resolved Near-Field Spectroscopy of Localized States in m -Plane InxGa1-x N/Ga N Quantum Wells
- 2017
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 7:6
-
Tidskriftsartikel (refereegranskat)abstract
- We present a polarization, spectrally, and spatially resolved near-field photoluminescence (PL) measurement technique and apply it to the study of wide m-plane InxGa1-xN/GaN quantum wells grown on on-axis and miscut GaN substrates. It is found that PL originates from localized states; nevertheless, its degree of linear polarization (DLP) is high with little spatial variation. This allows an unambiguous assignment of the localized states to InxGa1-xN composition-related band potential fluctuations. Spatial PL variations, occurring due to morphology features of the on-axis samples, play a secondary role compared to the variations of the alloy composition. The large PL peak wavelength difference for polarizations parallel and perpendicular to the c axis, the weak correlation between the peak PL wavelength and the DLP, and the temperature dependence of the DLP suggest that effective potential variations and the hole mass in the second valence-band level are considerably smaller than that for the first level. DLP maps for the long wavelength PL tails have revealed well-defined regions with a small DLP, which have been attributed to a partial strain relaxation around dislocations.
|
|
| 6. |
- Khachatourian, Malek Adrine, et al.
(författare)
-
Microwave synthesis of Y2O3:Eu3+ nanophosphors : A study on the influence of dopant concentration and calcination temperature on structural and photoluminescence properties
- 2016
-
Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 169, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- Red fluorescent emitting monodispersed spherical Y2O3 nanophosphors with different Eu3+ doping concentrations (0-13 mol%) are synthesized by a novel microwave assisted urea precipitation, which is recognized as a green, fast and reproducible synthesis method. The effect of Eu3+ doping and calcination temperature on the structural characteristics and luminescence properties of particles is investigated in detail. The as prepared powders have (Y,Eu)(OH)(CO3) structure which converts to Y2O3:Eu3+ from 500 °C and become crystalline at higher temperatures. The crystallite size of nanophosphors increased from 15 nm to 25 nm as the calcination temperature increased from 700 °C to 1050 °C. The efficient incorporation of Eu3+ ions in cubic Y2O3 host matrix is confirmed by the calculated X-ray Powder diffraction (XRPD) structural parameters. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs show that the as obtained and calcined particles are spherical, monodispersed and non-agglomerated. The overall size of particles increases from 61±8 nm to 86±9 nm by increasing Eu3+ concentration from 0 mol% to 13 mol%. High resolution TEM revealed polycrystalline nature of calcined particles. The particles exhibit a strong red emission under ultraviolet (UV) excitation. The photoluminescence (PL) intensity of the peaks increases proportionally with Eu3+ concentration and the calcination temperature with no luminescence quenching phenomenon observed even for Y2O3:13%Eu3+. The fluorescent emission properties combined with the monodispersity and narrow size distribution characteristics make the Y2O3:Eu3+ heavy metal free nanophosphors applicable in fluorescence cell imaging and as fluorescence biolabels.
|
|
| 7. |
- Klipfel, Nadja, et al.
(författare)
-
Mechanistic Insights into the Role of the Bis(trifluoromethanesulfonyl) imide Ion in Coevaporated p-i-n Perovskite Solar Cells
- 2021
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:44, s. 52450-52460
-
Tidskriftsartikel (refereegranskat)abstract
- Hybrid lead halide perovskites have reached comparable efficiencies to state-of-the-art silicon solar cell technologies. However, a remaining key challenge toward commercialization is the resolution of the perovskite device instability. In this work, we identify for the first time the mobile nature of bis-(trifluoromethanesulfonyl)imide (TFSI-), a typical anion extensively employed in p-type dopants for 2,2'7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'spirofluorene (spiro-OMeTAD). We demonstrate that TFSI- can migrate through the perovskite layer via the grain boundaries and accumulate at the perovskite/electrontransporting layer (ETL) interface. Our findings reveal that the migration of TFSI- enhances the device performance and stability, resulting in highly stable p-i-n cells that retain 90% of their initial performance after 1600 h of continuous testing. Our systematic study, which targeted the effect of the nature of the dopant and its concentration, also shows that TFSI- acts as a dynamic defect-healing agent, which self-passivates the perovskite crystal defects during the migration process and thereby decreases nonradiative recombination pathways.
|
|
| 8. |
- Krishna, Anurag, et al.
(författare)
-
Nanoscale interfacial engineering enables highly stable and efficient perovskite photovoltaics
- 2021
-
Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry. - 1754-5692 .- 1754-5706. ; 14:10, s. 5552-5562
-
Tidskriftsartikel (refereegranskat)abstract
- We present a facile molecular-level interface engineering strategy to augment the long-term operational and thermal stability of perovskite solar cells (PSCs) by tailoring the interface between the perovskite and hole transporting layer (HTL) with a multifunctional ligand 2,5-thiophenedicarboxylic acid. The solar cells exhibited high operational stability (maximum powering point tracking at one sun illumination) with a stabilized T-S80 (the time over which the device efficiency reduces to 80% after initial burn-in) of approximate to 5950 h at 40 degrees C and a stabilized power conversion efficiency (PCE) over 23%. The origin of high device stability and performance is correlated to the nano/sub-nanoscale molecular level interactions between ligand and perovskite layer, which is further corroborated by comprehensive multiscale characterization. These results provide insights into the modulation of the grain boundaries, local density of states, surface bandgap, and interfacial recombination. Chemical analysis of aged devices showed that molecular passivation suppresses interfacial ion diffusion and inhibits the photoinduced I-2 release that irreversibly degrades the perovskite. The interfacial engineering strategies enabled by multifunctional ligands can expedite the path towards stable PSCs.
|
|
| 9. |
- Marcinkevičius, Saulius, et al.
(författare)
-
Multimode scanning near-field photoluminescence spectroscopy and its application for studies of ingan epitaxial layers and quantum wells
- 2018
-
Ingår i: Lithuanian Journal of Physics. - : Lithuanian Academy of Sciences. - 1648-8504 .- 2424-3647. ; 58:1, s. 76-89
-
Tidskriftsartikel (refereegranskat)abstract
- The paper reviews our recent achievements in developing a multimode scanning near-field optical microscopy (SNOM) technique. The multimode SNOM apparatus allows us to simultaneously measure spatial variations of photoluminescence spectra in the illumination and illumination-collection modes, their transients and sample surface morphology. The potential of this technique has been demonstrated on a polar InGaN epitaxial layer and nonpolar InGaN/GaN quantum wells. SNOM measurements have allowed revealing a number of phenomena, such as the band potential fluctuations and their correlation to the surface morphology, spatial nonuniformity of the radiative and nonradiative lifetimes, as well as the extended band nature of localized states. The combination of different modes enabled measurements of the ambipolar carrier diffusion and its anisotropy.
|
|
| 10. |
- Marcinkevičius, Saulius, et al.
(författare)
-
Multimode scanning near-field photoluminescence spectroscopy of InGaN quantum wells
- 2018
-
Ingår i: 2018 IEEE RESEARCH AND APPLICATIONS OF PHOTONICS IN DEFENSE CONFERENCE (RAPID). - : IEEE. ; , s. 93-95
-
Konferensbidrag (refereegranskat)abstract
- Multimode scanning near-field photoluminescence spectroscopy was developed and applied to study carrier localization and dynamics in m-plane InGaN quantum wells. The study showed that localized hole states maintain properties of extended bands, radiative and nonradiative carrier lifetimes are spatially nonuniform, and hole diffusion is anisotropic.
|
|
