| 1. |
- Ghosh, Supriya, et al.
(författare)
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Light-induced defect healing and strong many-body interactions in formamidinium lead bromide perovskite nanocrystals
- 2020
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:4, s. 1239-1246
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Tidskriftsartikel (refereegranskat)abstract
- Organic lead halide perovskite (OLHP) nanocrystals (NCs) have paved the way to advanced optoelectronic devices through their extraordinary electrical and optical properties. However, understanding of the light-induced complex dynamic phenomena in OLHP NCs remains a subject of debate. Here we used wide field microscopy and time-resolved spectroscopy to correlate the local changes in photophysics and the dynamical behavior of photocarriers. We demonstrate that light-induced brightening of the photoluminescence from the formamidinium lead bromide NC films is related to the film preparation condition and reduction of trap density. The density of trap states is reduced via halide ion migration from interstitial position. Our femtosecond transient absorption study identifies transient Stark effect due to the generation of hot carriers. Because of slow carrier trapping, Auger recombination through many-body carrier-carrier interactions dominates over trion recombination. This work presents unprecedented insights into the light-driven processes enabling better device design in the future.
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| 2. |
- Ghosh, Supriya, et al.
(författare)
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Phonon Coupling with Excitons and Free Carriers in Formamidinium Lead Bromide Perovskite Nanocrystals
- 2018
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:15, s. 4245-4250
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Tidskriftsartikel (refereegranskat)abstract
- Organometal halide perovskites in the form of nanocrystals (NCs) have attracted enormous attention due to their unique optoelectronic and photoluminescence (PL) properties. Here, we examine the phase composition and the temperature dependence of emission line width broadening in formamidinium lead bromide (FAPbBr3) perovskite nanocrystals (NCs) for light-emitting applications and identify different charge-carrier scattering mechanisms. Our results show most of the emission is from the orthorhombic phase. The PL line width broadening at high temperature is dominated by the Fröhlich interaction between the free charge carriers and the optical phonons. At low temperatures, the peak of the PL spectrum exhibits a continuous red shift indicating an increase of excitons contribution at lower temperatures, and concurrently the line width also narrows down due to the inhibition of the optical phonons. From the temperature-dependent measurements, the coupling strength of both the charge phonon interaction and the exciton phonon interaction have been determined. The obtained results indicate that the charge phonon coupling strengths are higher compared to the exciton phonon coupling.
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| 3. |
- Ghosh, Supriya, et al.
(författare)
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Slower Auger Recombination in 12-Faceted Dodecahedron CsPbBr3 Nanocrystals
- 2023
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 14:4, s. 1066-1072
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Tidskriftsartikel (refereegranskat)abstract
- Over the past two decades, intensive research efforts have been devoted to suppressions of Auger recombination in metal-chalcogenide and perovskite nanocrystals (PNCs) for the application of photovoltaics and light emitting devices (LEDs). Here, we have explored dodecahedron cesium lead bromide perovskite nanocrystals (DNCs), which show slower Auger recombination time compared to hexahedron nanocrystals (HNCs). We investigate many-body interactions that are manifested under high excitation flux density in both NCs using ultrafast spectroscopic pump-probe measurements. We demonstrate that the Auger recombination rate due to multiexciton recombinations are lower in DNCs than in HNCs. At low and intermediate excitation density, the majority of carriers recombine through biexcitonic recombination. However, at high excitation density (>1018 cm-3) a higher number of many-body Auger process dominates over biexcitonic recombination. Compared to HNCs, high PLQY and slower Auger recombinations in DNCs are likely to be significant for the fabrication of highly efficient perovskite-based photonics and LEDs.
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| 4. |
- Zhang, Xin, et al.
(författare)
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An Integrated Bulk and Surface Modification Strategy for Gas-Quenched Inverted Perovskite Solar Cells with Efficiencies Exceeding 22%
- 2022
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Ingår i: Solar RRL. - : John Wiley & Sons. - 2367-198X. ; 6:6
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Tidskriftsartikel (refereegranskat)abstract
- Inverted perovskite solar cells (PSCs) prepared by the antisolvent method have achieved power conversion efficiencies (PCEs) of over 23%, but they are not ideal for device upscaling. In contrast, gas-quenched PSCs offer great potential for upscaling, but their performance still lags behind. Herein, the gas-quenched films through both surface and bulk modifications are upgraded. First, a novel surface modifier, benzylammonium thiocyanate, is found to allow remarkably improved surface properties, but the PCE gain is limited by the existence of longitudinally multiple grains. Thus, methylammonium chloride additive as a second modifier to realize monolithic grains is further utilized. Such an integrated strategy enables the average open-circuit voltage of the gas-quenched PSCs to increase from 1.08 to 1.15 V, leading to a champion PCE of 22.3%. Moreover, the unencapsulated device shows negligible degradation after 150 h of maximum power point operation under simulated 1 sun illumination in N2.
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