| 1. |
- Becker, Christiane, et al.
(författare)
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Nanophotonic enhanced perovskite-silicon solar cell devices
- 2019
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Ingår i: ; , s. 858-859
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Konferensbidrag (refereegranskat)abstract
- Perovskite-silicon tandem solar cells are a promising concept for overcoming the limits of conventional silicon single-junction technology. Light management is doubtless a key issue for further boosting efficiency. We discuss the impact of photonic nanostructures on the optical performance of perovskite-silicon devices. We experimentally and numerically demonstrate shallow antireflective nanotextures, which are compatible with perovskite solution processing. We further showcase enhanced photon up-conversion using perovskite nanoparticles interacting with photonic nanostructures and discuss the applicability for spectral conversion of sunlight.
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| 2. |
- Chen, Junsheng, et al.
(författare)
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Cation-Dependent Hot Carrier Cooling in Halide Perovskite Nanocrystals
- 2019
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 141:8, s. 3532-3540
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Tidskriftsartikel (refereegranskat)abstract
- Lead halide perovskites (LHPs) nanocrystals (NCs), owing to their outstanding photophysical properties, have recently emerged as a promising material not only for solar cells but also for lighting and display applications. The photophysical properties of these materials can be further improved by chemical engineering such as cation exchange. Hot carrier (HC) cooling, as one of the key photophysical processes in LHPs, can strongly influence performance of LHPs NCs based devices. Here, we study HC relaxation dynamics in LHP NCs with cesium (Cs), methylammonium (MA, CH 3 NH 3 + ), and formamidinium (FA, CH(NH 2 ) 2 + ) cations by using femtosecond transient absorption spectroscopy. The LHP NCs show excitation intensity and excitation energy-dependent HC cooling. We investigate the details of HC cooling in CsPbBr 3 , MAPbBr 3 , and FAPbBr 3 at three different excitation energies with low excitation intensity. It takes longer time for the HCs at high energy to relax (cool) to the band edge, compared to the HCs generated by low excitation energy. At the same excitation energy (350 nm, 3.54 eV), all the three LHP NCs show fast HC relaxation (<0.4 ps) with the cooling time and rate in the following order: CsPbBr 3 (0.39 ps, 2.9 meV/fs) > MAPbBr 3 (0.27 ps, 4.6 meV/fs) > FAPbBr 3 (0.21 ps, 5.8 meV/fs). The cation dependence can be explained by stronger interaction between the organic cations with the Pb-Br frameworks compared to the Cs. The revealed cation-dependent HC relaxation process is important for providing cation engineering strategies for developing high performance LHP devices.
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| 3. |
- Finkelstein-Shapiro, Daniel, et al.
(författare)
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Classification of dark states in multilevel dissipative systems
- 2019
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Ingår i: Physical Review A. - 2469-9926. ; 99:5
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Tidskriftsartikel (refereegranskat)abstract
- Dark states are eigenstates or steady states of a system that are decoupled from the radiation. Their use, along with associated techniques such as stimulated Raman adiabatic passage, has extended from atomic physics, where it is an essential cooling mechanism, to more recent versions in the condensed phase where it can increase the coherence times of qubits. These states are often discussed in the context of unitary evolution and found with elegant methods exploiting symmetries, or via the Morris-Shore transformation. However, the link with dissipative systems is not always transparent, and distinctions between classes of coherent population trapping are not always clear. We present a detailed overview of the arguments to find stationary dark states in dissipative systems, and examine their dependence on the Hamiltonian parameters, their multiplicity, and purity. We evidence the class of dark states that depends not only on the detunings of the lasers but also on their relative intensities and phases. We illustrate the criteria with the more complex physical system of the hyperfine transitions of Rb87 and show how a knowledge of the dark-state manifold can guide the preparation of pure states.
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| 4. |
- Han, Peigeng, et al.
(författare)
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Size effect of lead-free halide double perovskite on luminescence property
- 2019
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Ingår i: Science China Chemistry. - : Springer Science and Business Media LLC. - 1674-7291 .- 1869-1870. ; 62:10, s. 1405-1413
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Tidskriftsartikel (refereegranskat)abstract
- Lead-free halide double perovskites have gathered wide scientific interest since they are environmentally friendly and stable. However, compared to the lead perovskites, their optoelectronic properties are compromised. Herein we report a series of bulk lead-free mixed Bi-In halide double perovskites: Cs2AgBi1−xInxCl6 (0
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| 5. |
- Skov, Anders B., et al.
(författare)
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Excited‐State Topology Modifications of the Dihydroazulene Photoswitch Through Aromaticity
- 2019
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Ingår i: ChemPhotoChem. - : Wiley. - 2367-0932. ; 3:8, s. 619-629
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Tidskriftsartikel (refereegranskat)abstract
- The gain and loss of aromaticity plays a key role in organic chemistry and in the prediction of rate‐determining steps. Herein, we explore the concept of aromaticity in photoisomerization reactions. Benzannulated derivatives of the dihydroazulene‐vinylheptafulvene (DHA‐VHF) photoswitch were investigated using transient absorption spectroscopy and time‐dependent density functional theory to elucidate the effect of built‐in aromaticity on the switching properties. We found that benzannulation hampered the switching ability by enhancing an already existing barrier on the excited state surface. This enhancement was found to arise from a significant loss of aromaticity in the DHA‐to‐VHF transition state on the excited state potential energy surface. The VHF was found to be highly aromatic on the excited state surface, showing a reversal of aromaticity compared to the ground state. The barrier was found to be dependent on the position of benzannulation, since one derivative was found to switch as fast as the non‐benzannulated molecule although with lower efficiency, whereas another derivative completely lost the ability to undergo reversible photoswitching. The findings herein provide novel principles for the design of molecular photoswitches, shedding new light on excited state aromaticity, as previous discussions have mainly considered excited state aromaticity to be beneficial to switching. Our findings show that this view must be reconsidered.
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| 6. |
- Yan, Yajie, et al.
(författare)
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Benefiting from Spontaneously Generated 2D/3D Bulk-Heterojunctions in Ruddlesden−Popper Perovskite by Incorporation of S-Bearing Spacer Cation
- 2019
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Ingår i: Advanced Science. - : Wiley. - 2198-3844. ; 6:14
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Tidskriftsartikel (refereegranskat)abstract
- 2D Ruddlesden–Popper (RP) perovskite solar cells have manifested superior operation durability yet inferior charge transport compared to their 3D counterparts. Integrating 3D phases with 2D RP perovskites presents a compromise to maintain respective advantages of both components. Here, the spontaneous generation of 3D phases embedded in 2D perovskite matrix is demonstrated at room temperature via introducing S-bearing thiophene−2−ethylamine (TEA) as both spacer and stabilizer of inorganic lattices. The resulting 2D/3D bulk heterojunction structures are believed to arise from the compression-induced epitaxial growth of the 3D phase at the grain boundaries of the 2D phase through the Pb−S interaction. The as-prepared 2D TEA perovskites exhibit longer exciton diffusion length and extended charge carrier lifetime than the paradigm 2D phenylethylamine (PEA)-based analogues and hence demonstrate an outstanding power conversion efficiency of 7.20% with significantly increased photocurrent. Dual treatments by NH 4 Cl and dimethyl sulfoxide are further applied to ameliorate the crystallinity and crystal orientation of 2D perovskites. Consequently, TEA-based devices exhibit a stabilized efficiency over 11% with negligible hysteresis and display excellent ambient stability without encapsulation by preserving 80% efficiency after 270 h storage in air with 60 ± 5% relative humidity at 25 °C.
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| 7. |
- Yu, Shuang, et al.
(författare)
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Nonconfinement Structure Revealed in Dion–Jacobson Type Quasi-2D Perovskite Expedites Interlayer Charge Transport
- 2019
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 15:49
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Tidskriftsartikel (refereegranskat)abstract
- Dion–Jacobson (DJ) type 2D perovskites with a single organic cation layer exhibit a narrower distance between two adjacent inorganic layers compared to the corresponding Ruddlesden–Popper perovskites, which facilitates interlayer charge transport. However, the internal crystal structures in 2D DJ perovskites remain elusive. Herein, in a p-xylylenediamine (PDMA)-based DJ perovskite bearing bifunctional NH3 + spacer, the compression from confinement structure (inorganic layer number, n = 1, 2) to nonconfinement structure (n > 3) with the decrease of PDMA molar ratio is unraveled. Remarkably, the nonconfined perovskite displays shorter spacing between 2D quantum wells, which results in a lower exciton binding energy and hence promotes exciton dissociation. The significantly diminishing quantum confinement promotes interlayer charge transport leading to a maximum photovoltaic efficiency of ≈11%. Additionally, the tighter interlayer packing arising from the squeezing of inorganic octahedra gives rise to enhanced ambient stability.
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