1,720,994 research outputs found
Chloride-based route for monodisperse Cu2ZnSnS4 nanoparticles preparation
No full textA new approach based on hot injection method is proposed to gram-scale Cu2ZnSnS4 nanoparticles production minimizing the use of organic solvents. Nanocrystal synthesis was performed starting from metal chlorides and pure sulphur powder and using Oleylamine as capping agent. As a result, core-shell nanoparticles with a narrow size distribution were obtained. © 2015 AIP Publishing LLC
A water- and sulfurization-free solution route to Cu2-xZn1+xSnS4
No full textZinc-rich/copper-poor Cu2-xZn1+xSnS4 (x = 0.2, CZTS) has been successfully produced in film and powder form using two non-aqueous solutions (of metal salts and thiourea) without the need for sulfurization during the annealing phase. A reaction route is proposed and the choices of the solvents (water, ethyleneglycol, ethanol, methanol) and of the tin source (tin chloride pentahydrate or anhydrous) discussed and justified. A pure and coarse-grained material is obtained with a mix of metal salts in methanol and thiourea in ethylene glycol. The tin pentahydrate salt seems a better alternative to the commonly used anhydrous chloride
A simplified expression for optical absorbance in Si solar cells
No full textAn expression for optical absorbance in Si is derived, which is a simplification of the expression for the same quantity given by Basore. Unlike the Basore expression, the simplified expression does not require the determination of the front-surface external and internal reflectance prior to be used. For textured solar cells it is equivalent to the Basore expression, if the average ray-path angle with respect to the surface normal is equal at all passes of light across a cell. Unlike the Basore expression, it allows fitting the measured quantum efficiency of planar solar cells with diffuse rear surface. The simplified expression can be easily implemented in the numerical simulation program PC1d. The measured quantum efficiency of a textured solar cell is fitted with both the new and Basore expressions. Overlapping fit-curves are obtained. The measured quantum efficiency of a planar solar cell with not-polished rear surface is fitted by using the new expression. Finally, with the new expression, the maximum absorbance for weakly absorbed light is estimated in solar cells with textured back surface at both flat and textured front surfaces
Combinatorial study of co-sputtered Cu2ZnSnS4 thin-film stoichiometry for photovoltaic devices
No full textIn this work we investigate the role of stoichiometry variations in Cu2ZnSnS4 thin films obtained via sulfurization of precursor grown by co-sputtering of binary sulphides. Combinatorially graded thin-film Cu-Zn-Sn-S library samples spanning a large region of the ternary Cu2S-ZnS-SnS2 phase diagram were deposited at temperatures below 110°C and subsequently sulfurized at 550 °C in a tube furnace using a stoichiometric excess of sulfur. We present some results on the influence of chemical composition, measured by EDX, on the morphological and mechanical properties of the films. The films were also processed to obtain a matrix of small area complete photovoltaic devices. In this way the correlation between the stoichiometry and the device performances can be clarified. Finally, several interesting devices were more completely characterized by measuring J-V characteristic curves, the External Quantum Efficiency (EQE) and by looking at their photoluminescence (PL) spectrum trying to confirm a recently suggested correlation between PL peak energies and photovoltaic performances
Cu2SnS3 based solar cell with 3% efficiency
No full textCu2SnS3 is an earth abundant material suitable for photovoltaic applications. Unfortunately, the material still suffers of a low diffusion length of the carriers due to the presence of spurious phases, voids, defects and small grain size. In order to improve the quality of our samples, the influence of the deposition parameters on its structural properties has been studied. The solar cell obtained with the optimized Cu2SnS3 has shown an external quantum yield larger than 80% around 500 nm a conversion efficiency in the order of 3%, a Jsc of 26 mA and a Voc of 240 mV, one of the world best result obtained with a Cu2SnS3 based solar cell. Furthermore the external quantum yield at wavelength larger than 1200 nm is still around 30% making this material interesting for IR detectors also. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Perovskite and a-Si:H/c-Si tandem solar cell
No full textIn this work the fabrication of Perovskite/Si tandem-solar cell is reported and discussed. In principle this configuration allows cell efficiency higher than single c-Si junction. While Perovskite cell was used as top cell, a-Si:H/c-Si heterojunction was adopted as a bottom cell. The investigated process starts from Glass/FTO/c-TiO2/n-TiO2/CH3NH3PbI3/ Spiro-OMeTAD/ITO top cell, coupled to an ITO/a-Si:H/c-Si/back reflector/Al heterojunction bottom cell. ITO film is used to join the top and bottom cell. Preliminary results demonstrate the feasibility of the tandem cell, indeed Voc value as high as 1.65mV has been achieved. Numerical simulations is used to evaluate the limit and the potentiality of the proposed tandem structure. © 2015 IEEE
Electronic structure of Ar+ ion-sputtered thin-film MoS2: A XPS and IPES study
No full textPolycrystalline MoS2 grown by Mo sulphurization was exposed to increasing doses of Ar+ ions at 250 eV starting from 2.2 × 1015 ions/cm2 to 3.92 × 1017 ions/cm2. Electronic structure changes were monitored by X-Ray Photoelectron Spectroscopy (XPS) and Inverse Photolectron Spectroscopy (IPES). No change in the Fermi level position was observed with Ar+ dosing. Ion bombardment resulted in a new visible feature at lower binding energy in the Mo3d core level, while the S2p lineshape showed little changes. The formation of a steady state from 2.49 × 1017 ions/cm2 has been detected. The investigation of the occupied and unoccupied states on the steady-state surface pointed to the simultaneous presence of metallic-like Mo with amorphous MoS2-x. © 2016 Elsevier B.V
Effect of the order-disorder transition on the optical properties of Cu2ZnSnS4
No full textThe effect of the order-disorder transition on the band gap of kesterite Cu2ZnSnS4, an interesting material for solar cells, has been investigated by optical spectroscopy. The band gap energy (Eg) decreases continuously with increasing annealing temperature, Ta, and reaches its minimum at Ta ∼ 273 °C. Eg is about 200 meV higher in the most ordered state, than in the fully disordered state. Its value and the transition kinetic depend on the sample stoichiometry. A simplified model able to explain the order degree and stoichiometry effects on the Eg value is developed. Ordering results in narrower Raman peaks without affecting the shape of the photoluminescence spectrum - except for the change in Eg - or the characteristic energy of the exponential tail below the fundamental absorption edge. Although a prolonged annealing increases the order degree, the material properties are still influenced by residual disorder as well as by defects related to the off-stoichiometry composition
Evaluation of Hydrogen plasma effect in a-Si:H/c-Si interface by means of Surface Photovoltage measurement and FTIR spectroscopy
No full textThe amorphous/crystalline silicon technology has demonstrated its potentiality leading to high efficiency solar cells. To enhance the interface quality we investigate the effect of hydrogen plasma and thermal annealing treatments performed on thin amorphous silicon layer deposited over crystalline silicon surface. To this aim we use surface photovoltage technique, as a contact-less tool for the evaluation of the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to evaluate the evolution of Si-H and Si-H2 bonds. The surface photovoltage technique results to be very sensitive to the different experimental treatments, and therefore it can be considered a precious tool to monitor and improve the interface electronic quality. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, while the effect of hydrogen plasma post-treatment results more stable. In particular the latter reduces the defect density of one order of magnitude and keeps constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H+ ions accumulated during the plasma exposure, leading to a more stable configuration
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