We present the first steps toward the development of MoS2/Si heterojunctions photovoltaics, essentially for integrated photonic devices applications.
Therefore, we conjugate numerical device simulation, optical and structural characterizations, and density functional theory calculations. Through numerical device simulation, we show the potential of such solar cells, with attainable power conversion efficiencies of about 20%. Optical and structural characterizations of thin 2H-MoS2 layers deposited on SiO2 80nm/Si (001) substrates provides a path for the optimization of the 2D MoS2 material. With DFT calculations, we open the door for the optimization of the MoS2/Si interface, which is crucial for the device performances.
Perovskite-based solar cells (PSCs) have opened the possibility of cost-effective, high-efficiency photovoltaic conversion. However, their instabilities prevent them from commercialization. One of the instability triggers has been attributed to the mobile ions flowing into the carrier transport layer(s). To study the effect of this ionic migration, a numerical PSC model is developed, considering electronic and ionic mixed drift-diffusion transport both in the perovskite and the hole transport layer. The inverted PSC architecture, phenyl-C61-butyric acid methyl ester (PCBM)/perovskite/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with two heterojunctions, is analyzed. The effect of the ionic migration on the performance of the PSCs has been analyzed by (1) the variation of the ionic mobile concentration and (2) the modification of the local trapping density. The current–voltage (J–V) and capacitance–voltage characteristics show that the electric field in the bulk can be screened by the ionic distribution modifying the effective built-in voltage. At high ionic concentrations, the electric field at the interfaces is also affected, hindering the charge extraction. The simulations show that the short circuit current is therefore strongly modified.
A method based on DFT is used to obtained dielectric profiles. The high frequency Ɛ∞(z) and the static Ɛs(z) dielectric profiles are compared for 3D, 2D-3D and 2D Hybrid Organic Perovskites (HOP). A dielectric confinement is observed for the 2D materials between the high dielectric constant of the inorganic part and the low dielectric constant of the organic part. The effect of the ionic contribution on the dielectric constant is also shown. The quantum and dielectric confinements of 3D HOP nanoplatelets are then reported. Finally, a numerical simulation based on the SILVACO code of a HOP based solar cell is proposed for various permittivity of MAPbI3.
In this paper, we examine recent theoretical investigations on 3D hybrid perovskites (HOP) that combine concepts developed for classical bulk solid-state physics and empirical simulations of their optoelectronic properties. In fact, the complexity of HOP calls for a coherent global view that combines usually disconnected concepts. For the pseudocubic high temperature reference perovskite structure that plays a central role for 3D HOP, we introduce a new tight-binding Hamiltonian, which specifically includes spin-orbit coupling. The resultant electronic band structure is compared to that obtained using state of the art density functional theory (DFT). Next, recent experimental investigations of excitonic properties in HOP will be revisited within the scope of theoretical concepts already well implemented in the field of conventional semiconductors. Last, possible plastic crystal and orientational glass behaviors of HOP will be discussed, building on Car-Parrinello molecular dynamics simulations.
KEYWORDS: Optoelectronics, Spintronics, 3D modeling, Nanostructures, Optoelectronic devices, Photovoltaics, Transistors, Metals, Lead, Tin, Perovskite, System on a chip, Quantization, Solar cells, Semiconductors, Light emitting diodes, Control systems
In this paper, we propose a description of the Rashba-Dresselhaus effect in Hybrid Organic Perovskite (HOP). We show how the loss of the inversion symmetry leads to the loss of the spin degeneracy. An example of structure where both Rashba and Dresselhaus operate is illustrated with the formamidinium tin iodide CH(NH2)2SnI3. The control of this effect is as well addressed by two examples. A first example concerns the control with the temperature and is demonstrated for the 2D HOP Bz2PbCl4 (Bz = benzylammonium). Then the control with an external field is established for the 3D HOP CH3NH3PbBr3.
This paper reviews some of the recent theoretical investigations on the Rashba Dresselhaus spin effects and dielectric properties of CH3NH3PbI3 hybrid perovskites and CsPbI3 all-inorganic perovskites using Density functional theory. The spin vectors rotate in the non-centrosymmetric P4mm tetragonal phase, respectively clockwise and counterclockwise, in a manner that is characteristic of a pure Rashba effect. The high frequency dielectric constants ε∞ of MAPbI3 and CsPbI3 are similar as anticipated, since large differences are only expected at very low frequency where additional contributions from molecular reorientations show off for the hybrid compounds. A first simulation of a perovskite on silicon tandem cell, including a tunnel junction, is also investigated. Effect of halogen substitution (I/Br) is inspected, revealing limitations for short-circuit current and open-circuit voltage electrical characteristics.
KEYWORDS: System on a chip, Absorption, Solar cells, Crystals, Dye sensitized solar cells, Photovoltaics, Semiconductors, Chemical species, Cesium, Perovskite
Following pioneering works, the 3D hybrid lead-halide perovskites CH3NH3PbX3 (X=Cl, Br, I) have recently been shown to drastically improve the efficiency of Dye Sensitized Solar Cells (DSSC). It is predicted to open “a new era and a new avenue of research and development for low-cost solar cells … likely to push the absolute power conversion efficiency toward that of CIGS (20%) and then toward and beyond that of crystalline silicon (25%)” (Snaith, H. J. Phys Chem. Lett. 4, 3623-3630 (2013).). Here, we investigate theoretically the crystalline phases of one of the hybrids relevant for photovoltaic applications, namely CH3NH3PbCl3. Critical electronic states and optical absorption are thoroughly investigated both in the low and high temperature phases. Our findings reveal the dramatic effect of spin orbit coupling on their multiple band gaps. Their physical properties are compared to those of conventional semiconductors, evidencing inversion of band edge states.
Transparent conducting metal oxides (TCO) are unusual semiconducting materials displaying transparency to visible light. TCO materials are used for electrostatic shielding, antistatic screens, transparent heating devices, solar cells and even organic light emitting diodes. However, most TCOs are n-type, while p-type TCOs are scarce. SrCu2O2 is a leading candidate as a p-type transparent conductive oxide. In this paper, we report theoretical calculations and experimental studies on the vibrational, optical and microstructural properties of both bulk and thin films of polycrystalline undoped SrCu2O2 obtained by pulsed laser deposition (PLD). Barium doping of the SrCu2O2 by substitution of Sr atoms is also reported. The simulated crystal structures of both SrCu2O2 and BaCu2O2 materials, obtained through a state-of-the-art implementation of the Density functional theory, are compared with experimental X-ray diffraction data of undoped and Ba-doped SrCu2O2 bulk materials. Raman spectra of both SCO and BCO materials are simulated from the derivatives of the dielectric susceptibility and a symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. Good agreement with Raman scattering experimental results is demonstrated.
Lattice-matched GaP-based nanostructures grown on silicon substrates is a highly rewarded route for coherent
integration of photonics and high-efficiency photovoltaic devices onto silicon substrates. We report on the structural and
optical properties of selected MBE-grown nanostructures on both GaP substrates and GaP/Si pseudo-substrates. As a
first stumbling block, the GaP/Si interface growth has been optimised thanks to a complementary set of thorough
structural analyses. Photoluminescence and time-resolved photoluminescence studies of self-assembled (In,Ga)As
quantum dots grown on GaP substrate demonstrate a proximity of two different types of optical transitions interpreted as
a competition between conduction band states in X and Γ valleys. Structural properties and optical studies of
GaAsP(N)/GaP(N) quantum wells coherently grown on GaP substrates and GaP/Si pseudo substrates are reported. Our
results are found to be suitable for light emission applications in the datacom segment. Then, possible routes are drawn
for larger wavelengths applications, in order to address the chip-to-chip and within-a-chip optical interconnects and the
optical telecom segments. Finally, results on GaAsPN/GaP heterostructures and diodes, suitable for PV applications are
reported.
Thanks to optimized growth techniques, a high density of uniformly sized InAs quantum dots (QD) can be grown on
InP(113)B substrates. Low threshold currents obtained at 1.54 μm for broad area lasers are promising for the future. This
paper is a review of the recent progress toward the understanding of electronic properties, carrier dynamics and device
modelling in this system, taking into account materials and nanostructures properties. A first complete analysis of the
carrier dynamics is done by combining time-resolved photoluminescence experiments and a dynamic three-level model,
for the QD ground state (GS), the QD excited state (ES) and the wetting layer/barrier (WL). Auger coefficients for the
intradot assisted relaxation are determined. GS saturation is also introduced. The observed double laser emission for a
particular cavity length is explained by adding photon populations in the cavity with ES and GS resonant energies. Direct
carrier injection from the WL to the GS related to the weak carrier confinement in the QD is evidenced. In a final step,
this model is extended to QD GS and ES inhomogeneous broadening by adding multipopulation rate equations
(MPREM). The model is now able to reproduce the spectral behavior in InAs-InP QD lasers. The almost continuous
transition from the GS to the ES as a function of cavity length is then attributed to the large QD GS inhomogeneous
broadening comparable to the GS-ES lasing energy difference. Gain compression and Auger effects on the GS transition
are also be discussed.
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