Flexible perovskite solar cells (PSCs) show promise for next-gen photovoltaics, but achieving stability remains challenging, especially between rigid and flexible substrates. This study optimizes flexible PSCs' stability and reproducibility by selecting substrates, refining cleaning processes, and enhancing interfaces. Evaluating various substrates for flexibility, roughness, and perovskite compatibility, a meticulous cleaning protocol removes contaminants, improving perovskite-adhesive interactions. Emphasis on buried interfaces minimizes defects and boosts charge transport. Results show improved PSC efficiency (15.2% to 19.7%) and cycle durability (130 to 850 cycles, bending radius 5mm, reaching T80). Closing the performance gap, these findings advance reliable flexible PSCs for portable electronics, wearables, and building-integrated photovoltaics.
In this work, PSC with three different HTL dopants have been analyzed. By means of current-voltage characterization under light and dark conditions, EQE characterization in continuous, and transmittance spectral characterization we demonstrate that: (i) PSCs show an EQE peak efficiency in excess of 80% with a sharp edge at 550 nm, (ii) they show hysteresis in their electrical behavior, possibly due to ionic conduction; (iii) they show a good stability to reverse voltages down to -2.25 V. Being transparent at wavelengths above 550nm makes them suitable for agrivoltaic applications.
This work is focused on understanding the role that ferroelectric domains in methylammonium lead halide perovskite (MAPbI3) on the one hand and grain boundaries on the other can have on the performance of solar cells built from this material. We study 2D and 3D systems considering different polarization domain patterns, inspired by measurement data, by proposing a polarization model based on the knowledge of the crystalline structure, symmetry considerations and electrical simulations. Structures with grains are constructed from SEM data. We compute charge carrier transport by solving a drift-diffusion model, in which the Poisson equation for the electrostatic potential calculation explicitly includes the polarization field. The effects of grain boundaries are simulated by considering different types of trap states at the boundaries.
We show that the presence of polarization domains has a strong impact on charge separation, thus leading to a decrease of recombination losses and formation of current pathways at domain interfaces. Specifically, the decrease of Shockley-Read Hall recombination losses improves the open-circuit voltage, while the low resistivity current pathways lead to improved transport and an increase of the short-circuit current. The achieved results demonstrate that the presence of ordered ferroelectric domains, even with weak magnitude of polarization, can actually affect the performance of the solar cell in terms of enhanced power conversion. Moreover, from the comparison between our results and experimental IV characteristics of MAPb(I,Cl)3 devices we conclude that the polarization model proposed can effectively reproduce the solar cell operation.
During the last decade a number of both theoretical and experimental studies have shown the importance and the possible effects of random alloy fluctuations in InGaN. Interesting results have been obtained in particular with atomistic simulation models. Based on experimental evidence, most theoretical studies so far concentrated on a uniform random alloy, i.e. where the probability of finding an indium instead of a gallium atom is spatially constant.
In this work, we calculated the density of states, the spontaneous emission spectrum and the radiative coefficient for InGaN/GaN single quantum wells and for bulk InGaN in presence of alloy non-uniformity, using an empirical tight binding approach. We considered an indium concentration of 20%, and 10 nm large supercells. The non-uniform indium distribution has been obtained by distributing a certain percentage of all indium atoms with uniform probability, and the rest with a probability that depends on the number of indium atoms already present locally. This allows to produce structures ranging from random alloy up to strong clustering.
We find that non-uniformity reduces the band gap and the peak energy of the optical emission spectrum. Moreover, increasing degree of clustering decreases the average value of the ground state transition matrix element, which can be explained by the carriers’ spatial localization, combined with quantum confined Stark effect in quantum wells. The radiative coefficient on the other hand is not substantially influenced by light non-uniformity, while it increases for stronger degree of clustering, compatible with a transition to a quantum dot system.
In this work, we study the optical emission from arrays of InGaN/GaN MQW nanofin and nanorod arrays with sizes ranging from a few micrometers down to sub-wavelength dimensions (i.e., nanometers). Such systems are of interest for developing arrays of single addressable nanoLEDs, which could be used to obtain a visible wavelength super-resolution microscope where the resolution is due to highly localized light spots with sub-wavelength LED-to-LED pitch.
We have used commercial full-wave Maxwell solvers (COMSOL, CST) to calculate the optical field emitted from a single nanoLED in a periodic array for a wavelength of 450 nm. Simulations on 11×11 nanoLED arrays with pitches of 200 nm up to 800 nm and diameters of down to 50 nm have been conducted, in which the dependency of the emission pattern on different structural parameters is studied. In case of small nanoLED array with very narrow pitch, a large optical cross-talk between the activated LED and its neighboring pixels was found. Moreover, in presence of cross-talks, test objects smaller than the LED pitch placed on its surface with influence of near field could potentially be resolved by evaluating the varied emission patterns obtained by different pixel activations. Routes to achieve higher localized optical fields and reduce optical cross-talk have been also investigated by modifying the nanoLED array structures (e.g., by introducing filling material among the LED pixels).
Organic and inorganic materials are more and more frequently combined in high-performance hybrid electronic and photonic devices. For such multilayered stacks, the identification of layers and interface defects by depth profile analysis is a challenging task, especially because of the possible ion beam induced modifications. This is particularly true for perovskite solar cells stacks that in a mesoscopic structure usually combine a metal electrode, a mesoscopic conductive oxide layer, an intrinsically hybrid light absorber, an organic hole extraction layer and a metal counter electrode. While depth profile analysis with X-ray photoelectron spectroscopy (XPS) was already applied to investigate these devices, the X-ray and ion beam induced modifications on such hybrid layers have not been previously investigated. In this work we compare the profiles obtained with monatomic Ar+ beam at different energies, with the ones obtained with argon ion clusters (Arn+) with different sizes (150<n<1000) and energies (up to 8 keV). A systematic study is performed on full mesoscopic perovskite (CH3NH3PbI3) solar cells and on model hybrid samples ((FAxCs1-xPbI3)0.85 (MAPbBr3)0.15)/TiO2). The results show that for monatomic beams, the implantation of positively charged atoms induces the surface diffusion of free iodine species from the perovskite which modifies the I/Pb ratio. Moreover, lead atoms in the metallic state (Pb0 ) are found to accumulate at the bottom of the perovskite layer where the Pb0 /Pbtot fraction reaches 50%. With argon clusters, the ion beam induced diffusion of iodine is reduced only when the etch rate is sufficiently high to ensure a profile duration comparable with low-energy Ar+. Convenient erosion rates are obtained only for n=300 and n=500 clusters at 8 keV, which have also the advantage of preserving the TiO2 surface chemistry. However, with argon cluster ions, Pb0 particles in the perovskite are less efficiently sputtered which leads to the increase of the Pb0 /Pbtot fraction (up to 75%) at the perovskite/TiO2 interface. Finally, ion beam and X-ray induced artifacts on perovskite absorbers can be reasonably neglected for fast analysis conditions in which the exposure time is limited to few hours.
KEYWORDS: Dye sensitized solar cells, In vitro testing, Absorbance, Solar cells, Absorption, Visible radiation, Dysprosium, Magnesium, Ultraviolet radiation, In vivo imaging
In vitro grown shoots cultures (Prunus salicina × Prunus persica), elicited by methyl jasmonate (MJ), are reported here for the first time to prepare a natural dye for dye-sensitized solar cells (DSSC). Redox properties of the dye, its photostability, and light absorption properties suggested it as a candidate as natural photosensitizers for TiO2 photoelectrodes. Redox properties of the dye influence the DSSC production of photocurrent, thus three antioxidant assays were performed in order to characterize the antioxidant potential of this dye. The dye exhibited a high antioxidant activity in all the assays performed. Photostability assay revealed that the dye was quite stable to light. The power conversion efficiency that we obtained (0.53%) was comparable to the data by other authors with anthocyanins-based dyes from in vivo grown plants. Finally, we compared the dye with the partially purified one as photosensitizer in DSSC. The results indicated that the raw pigment from in vitro shoot cultures of P. salicina × P. persica elicited with MJ can be proposed without the needing of any other chemicals, thermal or purification process, or pH adjustments, as a dye for natural sensitized solar cells.
In this work we present a multiscale numerical simulation of solid-state Dye and Perovskite Solar Cells where the real morphology of the mesoporous active layer is taken into account. Band alignment and current densities are computed using the drift-diffusion model. In the case of Dye cells, a portion of the real interface is merged between two regions described using the effective medium approximation, casting light on the role of trapped states at the interface between TiO2 / Dye / hole transporting materials. A second case of study is the simulation of Perovskite Solar Cell where the performances of cells based on Alumina and Titania mesoporous layer are compared.
M. Dispenza, F. Brunetti, C.-S. Cojocaru, A. de Rossi, A. Di Carlo, D. Dolfi, A. Durand, A. Fiorello, A. Gohier, P. Guiset, M. Kotiranta, V. Krozer, P. Legagneux, R. Marchesin, S. Megtert, F. Bouamrane, M. Mineo, C. Paoloni, K. Pham, J. Schnell, A. Secchi, E. Tamburri, M. Terranova, G. Ulisse, V. Zhurbenko
Within the EC funded international project OPTHER (OPtically Driven TeraHertz AmplifiERs) a considerable
technological effort is being undertaken, in terms of technological development, THz device design and integration. The
ultimate goal is to develop a miniaturised THz amplifier based on vacuum-tube principles
The main target specifications of the OPTHER amplifier are the following:
- Operating frequency: in the band 0.3 to 2 THz
- Output power: > 10 mW ( 10 dBm )
- Gain: 10 to 20 dB.
The project is in the middle of its duration. Design and simulations have shown that these targets can be met with a
proper device configuration and careful optimization of the different parts of the amplifier. Two parallel schemes will be
employed for amplifier realisation: THz Drive Signal Amplifier and Optically Modulated Beam THz Amplifier.
Dye Sensitized solar cells (DSC) are an interesting alternative to conventional silicon based solar cells. Although
DSCs are very close to be commercialized, still many issues need to be addressed. Part of the problem is related
to the lack of a reliable and consistent simulator able to catch the physics and the chemistry underlining the
functioning of the cell. The need of a reliable simulator and modelling is particularly important for the engineering
of the cell and to define trends not only in the component characteristics, but also in the building of the device.
Among the different parts which compone a DSC the relevance of semiconductor titanium oxide substrate can
hardly be underestimated. TiO2 is where the dye molecule is chemisorbed and where the recombination occurs.
Moreover, changes in the topology of the semiconductor paste can lead to other smaller effects in the total
efficiency. In this paper we investigate the effects of changing working parameters for the titanium oxide and
varying its topology. The simulations are performed using a finite element code based on TiberCAD software1 to
describe in details the electrical properties of the cell. The CAD allows to calculate steady-state properties and
ideal I-V characteristics of the cell solving a set of differential equations on meshes in 1, 2 and 3 dimensions.
In this work we use the multi-scale software tool TiberCAD to study the transport and optical properties of InGaN
quantum disk (QD) - based GaN nanocolumn p-i-n diode structures. IV characteristics have been calculated for
several values of In concentration in the QD and of nanocolumn width. Strain maps show a clear relaxation effect
close to the column boundaries, which tends to vanish for the larger columns. Effects of strain and polarization
fields on the electron and hole states in the QD are shown, together with the dependence of optical emission
spectra on geometrical and material parameters.
In this work we develop a multiscale model to investigate the self-heating in nanodevices. The scheme splits up
the simulation region in two domains: the micro domain, modeled by the phonon Boltzmann Transport Equation
(BTE) and the macro domain, where the heat transport is calculated within the Fourier model. Appropriate
boundary conditions match the two domains. The multiscale method is applied to a GaN/AlGaN quantum dot
LED. We find out that the maximum temperature is about 334 K. A comparison with the temperature profile
given by the BTE and Fourier model is provided. Finally, the effect of the temperature on the optical spectrum
is investigated.
We present here some methods for the production of organized systems formed by carbon nanotubes and suitable for
nano-beams generation and handling. In particular methodologies based on Chemical Vapour Deposition (CVD),
chemically induced assembling and alignment by dielectrophoretic processes are examined and their capacity to produce
assembling of nanostructured materials with defined architecture is discussed
The importance of nanocomposites materials such as carbon nanotubes-polymers composites for the efficient realization
of innovative solar cells based on organic as well hybrid organic-inorganic solar cells is more and more evident. We
present a study on the realization of dye sensitized solar cells (DSSC) and sublimation deposited solar cells, considering
the impact of using nanocomposite materials in the different sections composing the cells. We discuss the effect of using
poly-3,4-ethylene dioxythiophene/poly(styrene sulfonate) (PEDOT/PSS)-Carbon nanotube (CNT) blend as counterelectrode
in DSSC on the cell efficiency and fill factor, also considering DSSC structures where low cost, innovative
dyes are used. Nanocomposites can be used as solution processed or electropolimerized electrodes, where accurate
control of nanotube dispersion is obtained through specific chemical treatment of Carbon nanotubes solubility. The use
of Carbon based nanostructured material is also investigated in terms of their positive impact on the realization of
organic solar cells on flexible substrates.
In the first part of the present contribution, we will report on transport calculations of nanoscaled devices based on Carbon Nanotubes obtained via self-consistent density-functional method coupled with non-equilibrium Green's function approaches. In particular, density functional tight-binding techniques are very promising due to their intrinsic efficiency. This scheme allows treatment of systems comprising a large number of atoms and enables the computation of the current flowing between two or more contacts in a fully self-consistent manner with the open boundary conditions that naturally arise in transport problems. We will give a description of this methodology and application to field effect transistor based on Carbon nanotubes.
The advances in manufacturing technology are allowing new opportunities even for vacuum electron devices producing radio-frequency radiation. Modern micro and nano-technologies can overcome the typical severe limitations of vacuum tube devices. As an example, Carbon Nanotubes used as cold emitters in micron-scaled triodes allow for frequency generation up to THz region. The purpose of the second part of this contribution will be a description of the modelling of Carbon Nanotube based vacuum devices such as triodes. We will present the calculation of important figures of merit and possible realizations.
We have performed studies on the correlation between mechanical deformations and electrical conductance on a new interesting hybrid material, a Single Wall Carbon Nanotubes (SWCNTs)/Poly(3,4-ethylenedioxythiophene) (PEDOT) composite. Two are the synthesis techniques utilized to prepare the composite material in form of few hundreds of nm thick films: a spin coating deposition starting from an aqueous dispersion of SWCNTs and PEDOT, and an electrochemical de*position starting from a dispersion of SWCNTs and EDOT monomer. The composite conductance changes induced by a modulated periodic elongation via a coherent technique have been monitored by measuring the voltage variations of a Wheatstone bridge connected with the films. The measurements were performed on SWCNTs/PEDOT composites layered on a rigid substrate. The piezoresistivity gauge factor (GF) of the various samples was evaluated by comparing their responses to mechanical deformations to those of a commercial strain gauge, sticked on a substrate of the same kind. We found no significant piezoresistive effect in the hybrid material films deposited by means of spin coating while the effect is remarkable for the composites prepared by means of the electrochemical technique. In this case the gauge factor is found to be up to 3-4 times higher than that of the commercial strain gauge.
We reported the design and realization of a carbon nanotube-based integrated multielectrode device. Patterned Si/SiO2/Nb/Nb2O5 multilayer was successfully realized by means of a few, common photolithographic processes with the minimum number of mask alignment steps. Such structure constitutes the patterned substrate of successive Hot Filament Chemical Vapour Deposition (HFCVD) process. Selective growth of highly oriented SWCNT arrays was obtained in the predefined locations while survival of the entire structure was achieved. Field emission measurements of such materials were carried out. Good and reproducible field emission behaviour has been observed in several realized structures.
In the present research, purified commercially SWCNTs are used as gas sensing material in an interdigitated electrode platform for NH3, NOx and H2O detection. The SWCNT response to gas absorption is known to be dependent from different parameters and operational conditions, such as the relative orientation of the nanotubes and their organization between the electrodes, the temperature of the sensor, and moreover the voltage applied to a back gate contact. We show the sensor response for the various gas species considered and we analyze the sensor behavior with respect to the sensibility and to the detection velocity. Moreover we studied the effect on absorption/desorption gas processes by applying a gate voltage to the Si substrate beneath the interdigitated electrodes. The results indicate that the acceleration of the time response of the sensor for the detection of NH3 is proportional to the gate voltage in the range 0 V - 40 V.
A recent study initiated by the European Space Agency aimed at identifying the most promising technologies to significantly improve on the generation of coherent electromagnetic radiation in the THz regime. The desired improvements include, amongst others, higher output powers and efficiencies at increasingly higher frequencies, wider tunability and miniaturization. The baseline technologies considered revolve around Photomixing and novel laser based technologies compared to all electronic techniques. Some of the most significant findings will be presented together with technological developments and experimental results selected for medium to short term development. These technologies include advanced p-i-n photomixer with superlattice structures and, THz quantum cascade lasers. Recent results achieved in these fields will be put into the potential perspective for the respective technology in the future.
We have investigated the electrical properties of organic thin-film transistor by using two-dimensional drift-diffusion simulations. The dependence of electrical haracteristics on the mobility model and on the barrier height of the contacts is carried out. We found that the field dependence of the carrier mobility is responsible for non-linearity of the drain current. This non-linear behavior is mainly related to the field-dependence of the mobility and to the barrier height of the contacts. The simulation allow us to clear understand the differences in the mobility derived by the analysis of I-V curve (as done experimentally by using standard MOSFET theory) and the intrinsic mobility of the organic layer. The effects of the interface traps has also be considered. The dependence of the threshold voltage on the density, energy level and model of the traps has been outlined. Results of the simulations have been compared with experimental data. The comparison between experimental data and
simulation allow us to clearly identify the physical mechanism responsible for the measured characteristics. Finally we also consider the effect of the device bending on the electrical characteristic of all-plastic OTFT.
In the present work we investigate the influence of molecular vibrations on the tunneling of electrons through a molecule sandwiched between two metal contacts. The study is confined to the elastic scattering only, but beyond the harmonic approximation. The problem is tackled both from a classical and a quantum-mechanical point of view. The classical approach consists in the computation of the time-dependent current uctuations calculated at each step of a molecular dynamics (MD) simulation. On the other hand, the vibrational modes are treated quantum-mechanically and the tunneling current is computed as an ensemble average over the distribution of
the atomic configurations obtained by a suitable approximation of the density matrix for the normal mode oscillators. We show that the lattice fluctuations modify the electron transmission. At low temperatures the quantum-mechanical treatment is necessary in order to correctly include the zero-point fluctuations. However, for temperatures higher than few hundreds Kelvin the simple harmonic approximation which leads to the phonon modes breaks because the oscillation amplitudes of the lowest energy modes become large.
Density Functional theory calculations combined with non-equilibrium Green's function technique have been used to compute electronic transport in organic molecules. In our approach the system Hamiltonian is obtained by means of a self-consistent density-functional tight-binding (DFTB) method. This approach allows a first-
principle treatment of systems comprising a large number of atoms. The implementation of the non-equilibrium Green's function technique on the DFTB code allows us to perform computations of the electronic transport properties of organic and inorganic molecular-scale devices. The non-equilibrium Green's functions are used to compute the electronic density self-consistently with the the open-boundary conditions naturally encountered in transport problems and the boundary conditions imposed by the potentials at the contacts. The Hartree potential of the density-functional Hamiltonian is obtained by solving the three-dimensional Poisson's equation involving the non-equilibrium charge density.
Single Wall Carbon Nanotubes (SWCNTs) based nanotechnology appears to be promising for future nanoelectronics. The SWCNT may be either metallic or semiconducting and both metallic and semiconducting types of SWCNTs have been observed experimentally. This gives rise to intriguing possibilities to put together semiconductor-semiconductor and semiconductor-metal junctions for diodes and transistors. The potential for nanotubes in nanoelectronics devices, displays and nanosensors is enormous. However, in order to realize the potential of SWCNTs, it is critical to understand the properties of charge transport and to control phase purity, elicity and arrangement according to specific architectures. We have investigated the electrical properties of various SWCNTs samples whit different organization: bundles of SWCNTs, SWCNT fibres and different membranes and tablets obtained using SWCNTs purified and characterized.
Electrical characterizations were carried out by a 4155B Agilent Semiconductor Parameter Analyser. In order to give a mechanical stability to SWCNTs fibres and bundles we have used a nafion matrix coating, so an electrical characterization has been performed on samples with and without this layer. I-V measurements were performed in vacuum and in air using aluminium interdigitated coplanar-electrodes (width=20mm or 40mm) on glass substrates. The behaviour observed is generally supralinear with currents of the order of mA in vacuum and lower values in air with the exception of the tablet samples where the behaviour is ohmic, the currents are higher and similar values of current are detected in air and vacuum.
We present a theoretical study of hot-carrier induced light emission in III-V semiconductor devices. Carrier heating under the intense electric fields present under high bias conditions are studied via a selfconsistent Monte Carlo simulation. The carrier distribution functions obtained from the simulation are then incorporated into a pseudo-potential algorithm that describes the direct optical transitions and calculates the corresponding spectra. We show that the light emission due to hot carriers is dominated by direct radiative interband transitions within the conduction and valence bands. Good agreement between theory and experiment is obtained for GaAs MESFET and GaAs/AlGaAs HBTs.
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