Numerous experiments have demonstrated improvements on the efficiency of perovskite solar cells by introducing plasmonic nanoparticles, however, the underlying mechanisms are still not clear: the ...particles may enhance light absorption and scattering, as well as charge separation and transfer, or the perovskite's crystalline quality. Eventually, it can still be debated whether unambiguous plasmonic increase of light absorption has indeed been achieved. Here, various optical models are employed to provide a physical understanding of the relevant parameters in plasmonic perovskite cells and the conditions under which light absorption may be enhanced by plasmonic mechanisms. By applying the recent generalized Mie theory to gold nanospheres in perovskite, it is shown that their plasmon resonance is conveniently located in the 650–800 nm wavelength range, where absorption enhancement is most needed. It is evaluated for which active layer thickness and nanoparticle concentration a significant enhancement can be expected. Finally, the experimental literature on plasmonic perovskite solar cells is analyzed in light of this theoretical description. It is estimated that only a tiny portion of these reports can be associated with light absorption and point out the importance of reporting the perovskite thickness and nanoparticle concentration in order to assess the presence of plasmonic effects.
The experimental literature on plasmonic perovskite solar cells is analyzed in light of this theoretical description. It is estimated that only a small portion of these reports can be associated with light absorption and point out the importance of reporting the perovskite thickness and nanoparticle concentration in order to assess the presence of plasmonic effects like localized surface plasmon resonance.
We demonstrate theoretically and experimentally that the three-dimensional orientation of a single fluorescent nanoemitter can be determined by polarization analysis of the emitted light (while ...excitation polarization analysis provides only the in-plane orientation). The determination of the emitter orientation by polarimetry requires a theoretical description, including the objective numerical aperture, the 1D or 2D nature of the emitting dipole, and the environment close to the dipole. We develop a model covering most experimentally relevant microscopy configurations and provide analytical relations that are useful for orientation measurements. We perform polarimetric measurements on high-quality core-shell CdSe/CdS nanocrystals and demonstrate that they can be approximated by two orthogonal degenerated dipoles. Finally, we show that the orientation of a dipole can be inferred by polarimetric measurement, even for a dipole in the vicinity of a gold film, while in this case, the well-established defocused microscopy is not appropriate.
Active control of the radiation orientation (beaming) of a metallic antenna has been reported by various methods, where the antenna excitation position was tuned with a typical 50 nm precision by a ...near-field tip or an electron-beam. Here we use optical microscopy to excite and analyze the fluorescence of a layer of nanocrystals embedded in an optical Tamm state nanostructure (metallic disk on top of a Bragg mirror). We show that the radiation pattern can be controlled by changing the excitation spot on the disk with only micrometer precision, in a manner which can be well described by numerical simulations. A simplified analytical model suggests that the propagation length of the in-plane confined optical modes is a key parameter for beaming control.
In this paper, we characterize the electric field distribution of confined optical modes in a 0D Tamm structure, consisting in a metallic disk deposited on a Bragg mirror. The modes are probed at ...room temperature, through the fluorescence of semiconductor colloidal nanocrystals. We perform a combined analysis of the resonant modes distribution in both direct space and Fourier space and show, in good agreement with numerical simulations, that a subportion of the structure will radiate with a different angular distribution depending on its position. Such analysis is shown to probe the gradient of the phase of the confined optical modes.
Many studies have considered the luminescence of colloidal II-VI nanocrystals, both in solution at a collective scale and at an individual scale by confocal microscopy. The quantum yield is an ...important figure of merit for the optical quality of a fluorophore. We detail here a simple method to determine the quantum yield of nanocrystals in solution as a function of the absorption. For this purpose, we choose rhodamine 101 as a reference dye to measure the nanocrystal fluorescence quantum yield. The influence of the concentration on quantum yield is therefore studied for both the reference and the solutions of nanocrystals and is found to be critical for the acuity of the method. Different types of nanocrystals are studied to illustrate different quantum yield evolutions with the concentration.
Opal-based photonic crystals are promising materials to engineer complex heterostructures for efficient manipulation of nano-emitters fluorescence. We fabricated and characterized a structure ...composed of a layer of silica embedded between two silica opals. Thanks to this controlled planar defect which opens a permitted frequency band in the photonic stopband, an increase of emission, depending on angular distribution, is evidenced through photoluminescence spectroscopy. We discuss the use of such a structure as a self-assembled micrometer-sized spectroscopic device and demonstrate that it can be used to point the maximum emission wavelength of an unknown light source up to a certain linewidth. It can as well separate two sources, emitting at different wavelengths, with a resolution given by the Rayleigh criterion.
We describe the preparation and characterization of photonic colloidal crystals from silica spheres with incorporated luminescent Mo
6
Br
14
2−
cluster units. These structures exhibit strong ...angle-dependent luminescent properties. The incorporation of one or several planar defects in the periodic structures gives rise to the creation of a passband in the stopband. In the energy range of this passband, an increase of the emission intensity has been found.
We have engineered colloidal crystals from silica spheres with incorporated luminescent Mo
6
Br
14
2−
cluster units.
To achieve large-scale commercialization of perovskite thin-film solar cells in the near future, improving perovskite thin-films quality and properties is becoming more and more critical. We focus ...here on the effect of introducing gold nanoparticles (Au_NPs) in MAPbI3 layers for solar cells. Experimentally, we show a 12% improvement of the stabilized efficiency by introducing an optimized amount of Au_NPs. The nanoparticles action has been addressed through a combination of experiments and optical simulations. First, we have calculated Mie absorption coefficients, done numerical FDTD simulations and transfer-matrix simulations to model the localized surface plasmon resonance (LSPR) and light scattering efficiency of Au_NPs. They have allowed us to state that, to reach a significant beneficial effect, the nanoparticle volume ratio must be above 1%, which is far above the content in our optimized perovskite solar cells layers. Only a negligible enhancement of light absorption can be attributed to the Au_NPs. Secondly, by combining several analysis techniques, especially by using glow discharge-optical emission spectroscopy (GD-OES), we reveal the mechanism of how Au_NPs improve the quality of perovskite films. The gold nanoparticles lead to the formation of monolithic grains with few defects and reduced grain boundaries which are the targeted properties for high efficiency. Therefore, in our devices, the effect of Au_NPs on the improvement of the quality of the perovskite layer is far more significant than that of the increase in light-harvesting. Finally, further performance and stability increases have been achieved by introducing the treatment of Au_NPs/MAPbI3 film surface by n-propylammonium iodide (PAI). It resulted in a power conversion efficiency of over 20%.
Display omitted
•Introducing gold nanoparticles in perovskite films boosts the efficiency of solar cells.•1% gold volume concentration is needed to yield a significant improvement by localized surface plasmon resonance (LSPR).•The optimum experimental nanoparticles concentration is 100 times lower than the one leading to significant LSPR effects.•Gold nanoparticles control the film growth direction and solvent elimination upon the layer annealing.•Gold Nanoparticles yield better perovskite crystals, large monolithic grains, less grain boundaries and structural defects.
As perovskite solar cells (PSC) are now reaching high power conversion efficiencies, further performance improvement requires a fine management and harvesting optimization of light in the cells. ...These request an accurate understanding, characterization and modelling of the optical processes occurring within these complex, often textured, multi-layered systems. We consider here a typical methylammonium lead iodide (MAPI) solar cell built on a fluorine-doped tin oxide (FTO) electrode of high roughness. We used variable-angle spectroscopic ellipsometry (VASE) to design a one-dimensional (1D) optical model of the stacked layers describing the rough texture as layers of effective-medium index. While most previous reports on PSC optical models performed ellipsometry only on single layers of each material independently deposited on glass, our model was obtained by an extensive ellipsometric analysis of the full stratified PSC structure at each deposition step. We support the 1D model using data extracted from scanning electron microscopy, diffuse spectroscopy and photovoltaic efficiency measurements and compare its results with full 3D simulations. Although the 1D model is insufficient to describe scattering by the FTO plate alone, it gives an accurate description of the full device optical properties. By comparison with the experimental external quantum efficiency (EQE), we estimate the internal quantum efficiency (IQE) and the effect of the losses related to electron transfer. We finally discuss the optical losses mechanisms and possible strategies to improve light management and further increase PSC performances.
•Many perovskite solar cells present complex 3D structures due to high roughness.•The cell can be modelled based on ellipsometric analysis of the full device.•The obtained 1D model is as adequate as a 3D model and leads to light extraction efficiency.
PDF
