Improving power conversion efficiency of perovskite solar cells by cooperative LSPR of gold-silver dual nanoparticles

Enhancing optical and electrical performances is effective in improving power conversion efficiency of photovoltaic devices. Here, gold and silver dual nanoparticles were imported and embedded in the hole transport layer of perovskite solar cells. Due to the cooperative localized surface plasmon resonance of these two kinds of metal nanostructures, light harvest of perovskite material layer and the electrical performance of device were improved, which finally upgraded short circuit current density by 10.0%, and helped to increase power conversion efficiency from 10.4% to 11.6% under AM 1.5G illumination with intensity of 100 m W/cm~2. In addition, we explored the influence of silver and gold nanoparticles on charge carrier generation, dissociation, recombination, and transportation inside perovskite solar cells.     

Control of the input efficiency of photons into solar cells with plasmonic nanoparticles

We study numerically the photon input efficiency of silicon solar cells due to gold plasmonic nanoparticles deposited on the cells. At low densities, when collective effects in light scattering by the nanoparticle ensemble are negligible, the absorption dependence increases linearly for a significant range of the solar spectrum. Collective effects lead to the input efficiency saturates, reaches its maximum and then decreases with nanoparticle density. The maximal input efficiency depends on the photon wavelength, nanoparticle shape and size, their distance to the cell, and the cell thickness, and can reach ~ 95% in thick solar cells. Finally, we show that aluminum nanoparticles improve the input efficiency in comparison with gold nanoparticles.     

Three dimensional a-Si:H thin-film solar cells with silver nano-rod back electrodes

We present three dimensional (3-D) amorphous silicon (a-Si:H) thin-film solar cells with silver nano-rods as back electrodes, which are fabricated by low cost nano imprint lithography (NIL). After conformal deposition of thin metal and semiconductor layers, we can achieve a dome-shaped geometry, which is shown to be effective in reducing the reflectance at the front surface due to the graded refractive index effect. In addition, the enhancement of the diffused reflectance over a broad wavelength in this dome-shaped geometry provides light trapping due to the increase in the effective light propagation length. Using this 3-D solar cell, we achieved 54% increase in short circuit current density and 45% increase in the conversion efficiency compared to the control cells with flat Ag surfaces. This 3-D structure can be also used for improving light harvesting in various photovoltaic devices regardless of materials and structures.     

Heterojunctions of TiO2 nanoparticle film and c-Si with different Fermi level positions

The photovoltaic properties of heterojunctions of titanium dioxide (TiO₂) nanoparticle films with single crystal silicon (c-Si) substrates with different Fermi level (E _f) positions were studied. The TiO₂ nanoparticles of rutile and anatase structures were studied without any sintering process. To clarify the photovoltaic properties, the characteristics of the heterojunction solar cells of TiO₂ nanoparticle films with p-Si and n-Si substrates were investigated, where several Si substrates with different resistivities were used. The I–V characteristics of p-Si/TiO₂ heterojunction showed the rectifying behavior and photovoltaic effect. The n-Si/TiO₂ heterojunction also showed good rectifying characteristics; however, the conversion efficiency was extremely lower than that of p-Si/TiO₂ heterojunction. The conversion efficiencies of various Si/TiO₂ (rutile) heterojunction solar cells against the Fermi level E _f of c-Si showed the maximum in the p-doped region. The photovoltaic properties of the Si/TiO₂ heterojunction also depended on the crystal structure of TiO₂, and the conversion efficiency of anatase is higher than that of rutile, which was attributed to the higher carrier mobility of anatase.     

Hydrodynamic size distribution of gold nanoparticles controlled by repetition rate during pulsed laser ablation in water

Most investigations on the laser generation and fragmentation of nanoparticles focus on Feret particle size, although the hydrodynamic size of nanoparticles is of great importance, for example in biotechnology for diffusion in living cells, or in engineering, for a tuned rheology of suspensions. In this sense, the formation and fragmentation of gold colloidal nanoparticles using femtosecond laser ablation at variable pulse repetition rates (100-5000 Hz) in deionized water were investigated through their plasmon resonance and hydrodynamic diameter, measured by Dynamic Light Scattering. The increment of the repetition rate does not influence the ablation efficiency, but produces a decrease of the hydrodynamic diameter and blue-shift of the plasmon resonance of the generated gold nanoparticles. Fragmentation, induced by inter-pulse irradiation of the colloids was measured online, showing to be more effective low repetition rates. The pulse repetition rate is shown to be an appropriate laser parameter for hydrodynamic size control of nanoparticles without further influence on the production efficiency.     

Organic photovoltaic materials and devices

Organic photovoltaic solar cells bere an important potential of development in the search for low-cost modules for the production of domestic electricity. We review the principles and techniques needed for their development: organic semiconductors, their transport properties and photophysical characteristics, photovoltaic molecule and polymer structures, device technologies, electrical and optical behaviour of the cells, state of the art, limitations and perspectives. Despite some recent record efficiencies, research on organic solar cells is still in its infancy when stability and efficiency have to be compared with the performances of silicon cells. A nominal 10% solar efficiency is the research target for the next few years. To cite this article: J.-M. Nunzi, C. R. Physique 3 (2002) 523–542.     

Impurity photovoltaic effect in silicon solar cell doped with sulphur: A numerical simulation

The impurity photovoltaic effect (IPV) has mostly been studied in various semiconductors such as silicon, silicon carbide and GaAs in order to increase infrared absorption and hence cell efficiency. In this work, sulphur is used as the IPV effect impurity incorporated in silicon solar cells. For our simulation we use the numerical device simulator (SCAPS). We calculate the solar cell performances (short circuit current density J_sc, open circuit voltage V_oc, conversion efficiency η and quantum efficiency QE). We study the influence of light trapping and certain impurity parameters like impurity concentration and position in the gap on the solar cell performances. Simulation results for IPV effect on silicon doped with sulphur show an improvement of the short circuit current and the efficiency for sulphur energy levels located far from the middle of the band gap especially at E_c-E_t=0.18 eV.     

One-step synthesis of silver nanoparticles in an aqueous solution and their antibacterial activities

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented in this research. In the synthesis, an amino-terminated hyperbranched polymer (HBP-NH₂) was applied as a stabilizer and a reductant. The syntheses, performed at various initial AgNO₃ concentrations (0.28–0.56 g/l) in a 2 g/l HBP-NH₂ aqueous solution, produced silver colloid nanoparticles having average sizes from 3 to 30 nm with narrow size distributions. The formation of silver colloid nanoparticles was characterized by Fourier Transform Infrared Spectrophotometry (FTIR), Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), UV/Visible Absorption Spectrophotometry, and X-ray Diffraction (XRD) measurements. The results indicated that both particle size and the UV absorption are strongly dependent on the initial AgNO₃ concentrations. The silver colloid nanoparticles, prepared with a 0.35 g/l AgNO₃ aqueous solution in the presences of 2 g/l HBP-NH₂, showed good antibacterial activities against Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). A very low concentration of nano-silver (as low as 3.0 ug/ml Ag) also gave excellent antibacterial performance.     

Surface plasmons for enhanced silicon light-emitting diodes and solar cells

Localized surface plasmons on metallic nanoparticles can be surprisingly efficient at coupling light into or out of a silicon waveguide. In this paper we review our recent work where we have demonstrated a factor of 8 times enhancement in the electroluminescence from a silicon-on-insulator light-emitting diode at 900 nm using silver nanoparticles, in the first report of a surface plasmon-enhanced silicon light-emitting diode. Our theoretical work has shown that the enhancement seen in this system at long wavelengths is mainly a single-particle effect, in contrast to previous suggestions that it is a waveguide-mediated multi-particle effect, and that there is a dramatic enhancement of the scattering cross-section for waveguided light in these devices. We discuss the route towards increasing this enhancement further and provide predictions of the limits on the maximum potential efficiency enhancement, as well as the potential of metal particles for applications in thin film silicon solar cells.     

Influence of SiNx:H film properties according to gas mixture ratios for crystalline silicon solar cells

The Hydrogenated silicon nitride (SiN_x:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. In the high temperature firing process, the SiN_x:H film should not change the properties for its use as high quality surface layer in crystalline silicon solar cells. For optimizing surface layer in crystalline silicon solar cells, by varying gas mixture ratios (SiH₄ + NH₃ + N₂, SiH₄ + NH₃, SiH₄ + N₂), the hydrogenated silicon nitride films were analyzed for its antireflection and surface passivation (electrical and chemical) properties. The film deposited with the gas mixture of SiH₄ + NH₃ + N₂ showed the best properties in before and after firing process conditions.The single crystalline silicon solar cells fabricated according to optimized gas mixture condition (SiH₄ + NH₃ + N₂) on large area substrate of size 156 mm × 156 mm (Pseudo square) was found to have the conversion efficiency as high as 17.2%. The reason for the high efficiency using SiH₄ + NH₃ + N₂ is because of the good optical transmittance and passivation properties. Optimized hydrogenated silicon nitride surface layer and high efficiency crystalline silicon solar cells fabrication sequence has also been explained in this study.     

Semiconductor solar cells: Recent progress in terrestrial applications

In the last decade, the photovoltaic industry grew at a rate exceeding 30% per year. Currently, solar-cell modules based on single-crystal and large-grain polycrystalline silicon wafers comprise more than 80% of the market. Bulk Si photovoltaics, which benefit from the highly advanced growth and fabrication processes developed for microelectronics industry, is a mature technology. The light-to-electric power conversion efficiency of the best modules offered on the market is over 20%. While there is still room for improvement, the device performance is approaching the thermodynamic limit of ∼28% for single-junction Si solar cells. The major challenge that the bulk Si solar cells face is, however, the cost reduction. The potential for price reduction of electrical power generated by wafer-based Si modules is limited by the cost of bulk Si wafers, making the electrical power cost substantially higher than that generated by combustion of fossil fuels. One major strategy to bring down the cost of electricity generated by photovoltaic modules is thin-film solar cells, whose production does not require expensive semiconductor substrates and very high temperatures and thus allows decreasing the cost per unit area while retaining a reasonable efficiency. Thin-film solar cells based on amorphous, microcrystalline, and polycrystalline Si as well as cadmium telluride and copper indium diselenide compound semiconductors have already proved their commercial viability and their market share is increasing rapidly. Another avenue to reduce the cost of photovoltaic electricity is to increase the cell efficiency beyond the Shockley–Queisser limit. A variety of concepts proposed along this avenue forms the basis of the so-called third generation photovoltaics technologies. Among these approaches, high-efficiency multi-junction solar cells based on III–V compound semiconductors, which initially found uses in space applications, are now being developed for terrestrial applications. In this article, we discuss the progress, outstanding problems, and environmental issues associated with bulk Si, thin-film, and high-efficiency multi-junction solar cells.     

Spectral-splitting concentrator photovoltaic modules based on AlGaAs/GaAs/GaSb and GaInP/InGaAs(P) solar cells

A concentrator photovoltaic module with sunlight spectral splitting by Fresnel lens and dichroic filters is developed. The photoelectric conversion efficiency of such a module is estimated at a level of 49.4% when three single-junction cells are used and may reach 48.5–50.6% when a tandem two-junction cell is combined with narrow-band cells. Single-junction AlGaAs, GaAs, GaSb, and InGa(P)As solar sells are fabricated by zinc diffusion from the vapor phase into an n-type epitaxial layer. GaInP/GaAs cascade solar cells are prepared by MOS hydride epitaxy. The overall efficiency of the three single-junction solar cells developed for the spectral-splitting module is 38.1% (AM1.5D) at concentration ratio K _c = 200x. The combination of the solar cells with the cascade structure demonstrates an efficiency of 37.9% at concentrations of 400–800 suns. The parameters of the spectral-splitting photovoltaic module are measured. The photovoltaic efficiency of this module reaches 24.7% in the case of three single-junction cells and 27.9% when the two-junction and single-junction cells are combined.     

n-Type microcrystalline silicon oxide layer and its application to high-performance back reflectors in thin-film silicon solar cells

Light trapping is a key issue in improving the efficiency of thin-film Si solar cells, and using a back reflector material plays a critical role in improving a cell's light-trapping efficiency. In this study, we developed n-type microcrystalline silicon oxide (n-μc-SiO_x) films that are suitable for use as back reflectors in thin-film silicon solar cells. They exhibit a lower refractive index and lower absorption spectra, especially at long wavelengths of >700 nm, than conventional ZnO:Al materials, which are beneficial for this application. The n-μc-SiO_x films were prepared by the PECVD (plasma-enhanced chemical vapor deposition) method and applied to the fabrication of back reflectors in μc-Si:H solar cells. We also characterized the changes in cell performance with respect to the refractive index, conductivity, and thickness of the n-μc-SiO_x back reflectors. The novel back reflector boosts the total current density by up to 3.0% with the help of the enhanced long-wavelength response. It also improves open circuit voltage (V_oc) and fill factor (FF), which may be attributed to the reduced shunt current caused by the anisotropic electrical characteristics of the n-μc-SiO_x layer. Finally, we could achieve a conversion efficiency for the hydrogenated microcrystalline silicon (μc-Si:H) solar cells of up to 9.3% (V_oc: 0.501 V, J_sc: 27.4 mA/cm², FF: 0.68) using the n-μc-SiO_x back reflector.     

Effects of silver nanoparticles towards the efficiency of organic solar cells

We report an alternative approach to enhance the optical and electrical performance of a vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine:poly(3hexylthiophene) (VOPcPhO:P3HT) blending system by integrating plasmonic spherical silver into an active layer of organic solar cells. Studies of the influence of the size distribution and optical properties of the silver nanoparticles were carried out using UV–Vis spectroscopy and field emission scanning electron microscopy, respectively. Electrical characteristics with and without the presence of metallic nanostructures were analyzed using J–V characteristics to observe the plasmonic effects on the performance in the VOPcPhO:P3HT organic solar cells.     

High-efficient Schottky-junction silicon solar cell using silver nanowires covering nitrogen-doped amorphous carbon

Synthesized graphene (Gr) on metal substrates that requires additional surface-to-surface transfer procedure to form Gr-on-silicon (Gr-Si) Schottky-junction configuration, which in turn results in the photovoltaic degradation caused by both mechanical damages and chemical contaminations during several wet chemical steps. This current issue has motivated us to develop alternative Schottky-junction configuration using silver nanowires (AgNWs) covering nitrogen (N)-doped amorphous carbon (a-C) films annealed in the temperature range 750–900 °C. Compared to the Schottky-junction Si solar cell based on 900 °C annealed N-doped a-C films (C_N-900-Si) with only Ag grid, all of AgNWs-C_N-900-Si solar cells exhibit the significant enhancement of photovoltaic characteristics. Consequently, the remarkable power conversion efficiency (PCE) of 6.17% is achieved on 0.2 wt% AgNWs-C_N-900-Si solar cell, which is far superior to that of the C_N-900-Si solar cell with only Ag grid (~0.13%). Furthermore, the 0.2 wt% AgNWs-C_N-900-SiNWs solar cell shows the highest short-circuit current density (J_SC) of 23.42 mA/cm² and PCE of 7.67%, which is a PCE enhancement of ~24% when compared to the 0.2 wt% AgNWs-C_N-900-Si solar cell. This study demonstrates that AgNWs network can accelerate the charge carrier extraction from Schottky-contact between C_N-900 and n-Si substrate, leading to greatly reduced series resistance that results in significantly enhanced photovoltaic characteristics.     

Thin film silicon nanowire photovoltaic devices produced with gold and tin catalysts

Silicon nanowires produced using pulsed plasma-enhanced chemical vapor deposition have been used as part of a thin film photovoltaic device. Nanowires of differing morphologies were produced by using both gold and tin thin films as a catalyst for growth. A prototype silicon nanowire-based thin-film photovoltaic device was produced by using doped silicon nanowires as the p-layer. Amorphous silicon was used as the intrinsic and n-layers of the device. The nanowires used in the photovoltaic devices had an average diameter of 420 nm after the deposition and coating of amorphous silicon intrinsic and n-layers. The nanowires were deposited in bulk as films of 3 to 42 μm in thickness. The resulting device, although of low efficiency, had a demonstrable photocurrent. Tin-catalyzed nanowires were found to produce a thin-film device with a measurable photocurrent whereas gold-catalyzed silicon nanowires did not. This was attributed to the length of the nanowires and thickness of the p-layer produced when using gold-catalyzed nanowires.     

Simulation of IPV effect in In-doped c-Si with optimized indium concentration and layer thickness

Impurity photovoltaic effect(IPV) is one of the attempts to improve efficiency of solar cells and is the idea of exploiting three step generation via impurity states within the band gap to utilize sub-band gap photons. The three transitions are of electrons from valence band (VB) to conduction band (CB), valence band to impurity level and impurity level to conduction band. In the present simulation, we have used the p⁺nn⁺ structure in order to achieve higher photogenerated current and efficiency without loosing the open circuit voltage. Compared to other group-III elements in silicon solar cell, Indium is the most suitable material to achieve higher benefit in IPV. In this simulation, the model of IPV is considered to achieve the maximum benefit from the impurity state in a solar cell. To simulate we have used the one dimensional simulation program, SCAPS-1D. Again light trapping is an important part of IPV solar cell that has been considered in this simulation. Using IPV we have numerically demonstrated, an increase in efficiency, by 2.79% over that without-IPV effect and a 3.23% increase over the efficiency, 30.9% as reported by Schmeits and Mani [1].     

High-resolution mapping of the energy conversion efficiency of solar cells and silicon photodiodes in photovoltaic mode

We demonstrate an optical technique to derive the two-dimensional energy conversion efficiency (η_CE), fill factor (FF) and external quantum efficiency (η_QE) distributions across the surface of photovoltaic devices. A compact, inexpensive optical-feedback laser diode microscope is constructed to acquire the confocal reflectance and efficiency maps enabling the observation of the local parametric behavior in silicon photodiodes in photovoltaic mode and single-junction solar cells. The η_CE and η_QE distributions are greatly influenced by local parasitic resistances that depend on laser irradiance. These parasitic resistances decrease the η_CE and η_QE values with distance from the contact electrode at high laser irradiance. The optical technique enables microscopic comparison of η_CE and η_QE within the pn-overlay region of the photodiode sample, revealing its optimization for photodetection rather than power generation. The technique also elucidates the decreasing local η_CE of the solar cell under intense irradiation.     

Influence of the semiconductor/metal rear contact on the performance of n(a-Si:H)/i(a-Si:H)/p(c-Si) heterojunction solar cells

The aim of this work is to analyze on the results of using of Al/Ag layer as a rear contact to improve the performance of heterojunction silicon solar cells. An analytical method is presented to extract the physical parameters of the equivalent circuit. These parameters are extracted to simulate the I(V) characteristic of heterojunction silicon solar cells, with Al and Al/Ag rear-metal contact. A good agreement between our analytical method and experimental measurement of electrical characteristics is obtained which show clearly how the Al/Ag rear contact can improve the characteristics of silicon solar cells. The influence of the rear-metal contact on the performance of the c-Si(p)-based bifacial HIT solar cell, i.e., the ZnO/Al/a-Si:H(n)/a-Si:H(i)/c-Si(p)/metal solar cell, is investigated in detail by computer simulation using the AFORS-HET software. Accordingly, the design optimization of the bifacial HIT solar cells on c-Si(p) substrates is provided. These simulation show an optimal conversion efficiency of 23% when the rear-metal contact is perfectly ohmic.     

19.4%‐efficient large‐area fully screen‐printed silicon solar cells

We demonstrate industrially feasible large‐area solar cells with passivated homogeneous emitter and rear achieving energy conversion efficiencies of up to 19.4% on 125 × 125 mm² p‐type 2–3 Ω cm boron‐doped Czochralski silicon wafers. Front and rear metal contacts are fabricated by screen‐printing of silver and aluminum paste and firing in a conventional belt furnace. We implement two different dielectric rear surface passivation stacks: (i) a thermally grown silicon dioxide/silicon nitride stack and (ii) an atomic‐layer‐deposited aluminum oxide/silicon nitride stack. The dielectrics at the rear result in a decreased surface recombination velocity of S_rear = 70 cm/s and 80 cm/s, and an increased internal IR reflectance of up to 91% corresponding to an improved J_sc of up to 38.9 mA/cm² and V_oc of up to 664 mV. We observe an increase in cell efficiency of 0.8% absolute for the cells compared to 18.6% efficient reference solar cells featuring a full‐area aluminum back surface field. To our knowledge, the energy conversion efficiency of 19.4% is the best value reported so far for large area screen‐printed solar cells. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)