Thin Film Silicon Photovoltaics Research Articles

Testing the effect of semi-transparent spectrally selective thin film photovoltaics for agrivoltaic application: A multi-experimental and multi-specific approach

The integration of photovoltaic technologies within the agricultural framework, known as agrivoltaics, emerges as a promising and sustainable solution to meet the growing global demands for energy and food production. This innovative technology enables the simultaneous utilization of sunlight for both photovoltaics (PV) and photosynthesis. A key challenge in agrivoltaic research involves identifying technologies applicable to a wide range of plant species and diverse geographic regions. To address this challenge, we adopt a multi-experimental and multi-species approach to assess the viability of semi-transparent, spectrally selective thin-film silicon PV technology. Our findings demonstrate compatibility with crop production in controlled environments for both plants and algae. Notably, selective thin-film PV exhibits the potential to enhance crop yields and serves as a photo-protectant. We observe that plant and algal growth increases beneath the selective PV film when supplemented with appropriate diffuse light in the growth environment. Conversely, in situations where light intensity exceeds optimal levels for plant growth, the selective PV film provides a photo-protective effect. These results suggest potential supplementary benefits of employing this technology in regions characterized by excessive light irradiation, where it can contribute to healthy plant growth.

Electrically Detected Magnetic Resonance on a Chip (EDMRoC) for Analysis of Thin-Film Silicon Photovoltaics

Electrically detected magnetic resonance (EDMR) is a spectroscopic technique that provides information about the physical properties of materials through the detection of variations in conductivity induced by spin-dependent processes. EDMR has been widely applied to investigate thin-film semiconductor materials in which the presence of defects can induce the current limiting processes. Conventional EDMR measurements are performed on samples with a special geometry that allows the use of a typical electron paramagnetic resonance (EPR) resonator. For such measurements, it is of utmost importance that the geometry of the sample under assessment does not influence the results of the experiment. Here, we present a single-board EPR spectrometer using a chip-integrated, voltage-controlled oscillator (VCO) array as a planar microwave source, whose geometry optimally matches that of a standard EDMR sample, and which greatly facilitates electrical interfacing to the device under assessment. The probehead combined an ultrasensitive transimpedance amplifier (TIA) with a twelve-coil array, VCO-based, single-board EPR spectrometer to permit EDMR-on-a-Chip (EDMRoC) investigations. EDMRoC measurements were performed at room temperature on a thin-film hydrogenated amorphous silicon (a-Si:H) pin solar cell under dark and forward bias conditions, and the recombination current driven by the a-Si:H dangling bonds (db) was detected. These experiments serve as a proof of concept for a new generation of small and versatile spectrometers that allow in situ and operando EDMR experiments.

Review of lead-free halide perovskites as light-absorbers for photovoltaic applications: From materials to solar cells

Metal halide perovskite materials have revolutionized the solution-processed solar cells and become the vanguard of research focus with an unprecedented improvement of power conversion efficiencies up to 23.3%, which pose a remarkable challenge to thin film and multicrystalline silicon photovoltaics. Nevertheless, for conventional perovskite solar cells based on lead, it is ineluctable to take the toxicity of lead and the long-term stability of the devices into consideration when the deployment of this technology in mass production is put on the agenda. To tackle the toxicity concern, extensive research effort has been devoted to the development of environmentally friendly lead-free halide perovskites for photovoltaic applications. Herein, we review the advancements in this emerging research area and discuss potential alternative elements to replace lead within the halide perovskite lattice. Particular attention will be focused on the properties of the corresponding perovskites and the relevant production of high efficiency photovoltaic devices, with the aim of identifying the materials to be competitive with lead-based perovskites. For the moment, tin-based perovskites appear likely to be the most preeminent from the point view of power conversion efficiency, despite the stabilities of the materials and the related devices are far from satisfaction. The introductions of germanium, bismuth, antimony, and certain transitional metals into perovskites brought about promising optoelectronic properties as well. This booming class of compounds constitutes unexplored territory and emerges as an affordable and robust candidate for green solar technology.

Solar vanadium redox-flow battery powered by thin-film silicon photovoltaics for efficient photoelectrochemical energy storage

Solar-powered vanadium redox-flow batteries (VRFB) have emerged as an attractive method for large-scale and efficient energy storage and conversion. However, due to the stringent charging voltage requirements of vanadium-based systems (1.4–1.7 V), common photobatteries, applying standard photovoltaics with nonoptimized photovoltages, cannot be completely charged bias-free, i.e. by only using bias-free solar energy, or if they can be, only at unpractical low current densities of just a few mA cm−2. In response to this critical challenge, the present study aimed to design and test a compact device combining a high-photovoltage silicon multijunction solar cell with an all-vanadium continuous-flow battery. In particular, we applied a monolithic triple junction solar cell, which can provide photovoltage of up to 2.2 V. Additionally, we have introduced the concept of increased illumination intensity for the solar VRFB. As a first demonstration, a complete bias-free solar charging at 25 mA cm−2 (300 mW cm−2 illumination) is reported. Moreover, we investigated the influence of the operation parameters of the redox-flow battery itself: the membrane type and the vanadium concentration in the electrolyte (i.e. storage capacity). The presented results provide evidence that the low-cost thin-film silicon based solar VRFB can be considered as an outstanding alternative for practical energy storage and conversion usage. A maximum bias-free solar conversion efficiency of 12.3% was achieved during charging, combined with promising and competitive energy efficiencies for the complete charge–discharge process that can guarantee an overall solar-to-electricity conversion efficiency of >10%.

Fabrication of Photovoltaic Textiles

Solar photovoltaic (PV) arrays are providing an increasing fraction of global electrical demand, with an accelerating rate of new installations. Most of these employ conventional glass-fronted panels, but this type of PV array does not satisfy applications that require a light-weight, flexible PV generator. An option discussed in this article is to consider textiles for such solar cell substrates. As explained in this review, combining the choice of PV cell type with the choice of textile offers alternative structures for flexible PV cells. In particular, the relative advantages and disadvantages are contrasted, either forming PV-coated fibres into a fabric, or coating an already formed fabric with the PV materials. It is shown that combining thin-film amorphous silicon PV technology and woven polyester fabric offers one solution to realizing flexible fabric PV cells, using well-understood coating methods from the textile and semiconductor industries. Finally a few applications are presented that are addressed by this approach.

Thin Film Silicon Photovoltaic Cells on Paper for Flexible Indoor Applications

The present development of non‐wafer‐based photovoltaics (PV) allows supporting thin film solar cells on a wide variety of low‐cost recyclable and flexible substrates such as paper, thereby extending PV to a broad range of consumer‐oriented disposable applications where autonomous energy harvesting is a bottleneck issue. However, their fibrous structure makes it challenging to fabricate good‐performing inorganic PV devices on such substrates. The advances presented here demonstrate the viability of fabricating thin film silicon PV cells on paper coated with a hydrophilic mesoporous layer. Such layer can not only withstand the cells production temperature (150 °C), but also provide adequate paper sealing and surface finishing for the cell's layers deposition. The substances released from the paper substrate are continuously monitored during the cell deposition by mass spectrometry, which allows adapting the procedures to mitigate any contamination from the substrate. In this way, a proof‐of‐concept solar cell with 3.4% cell efficiency (41% fill factor, 0.82 V open‐circuit voltage and 10.2 mA cm−2short‐circuit current density) is attained, opening the door to the use of paper as a reliable substrate to fabricate inorganic PV cells for a plethora of indoor applications with tremendous impact in multi‐sectorial fields such as food, pharmacy and security.

Optimization of Silver Nanotoroid Arrays for the Absorption Enhancement of Silicon Thin-Film Solar Cells

The enhancement of absorbed electromagnetic energy of thin-film silicon photovoltaics due to toroid-shaped plasmonic nanoparticles is computationally investigated. Using Ansys® HFSS, infinite arrays of silver nanotoroids of various sizes are tuned to maximize the photocurrent generation of the photovoltaic. The obtained results show that larger nanotoroid arrays can be tuned to provide enhanced photocurrent generation that is comparable to traditional sphere-shaped nanoparticles. The highly tunable nature of the resonant frequencies of plasmonic nanotoroid geometries is investigated here, which hold potential advantage over nanoparticles in their ability to enhance electromagnetic energy absorption in the longer wavelength regime of the solar spectrum. The obtained results show that larger nanotoroid arrays can be tuned to provide enhanced photocurrent generation comparable to traditional nanoparticles.

Comparison of thin epitaxial film silicon photovoltaics fabricated on monocrystalline and polycrystalline seed layers on glass

AbstractWe fabricate thin epitaxial crystal silicon solar cells on display glass and fused silica substrates overcoated with a silicon seed layer. To confirm the quality of hot‐wire chemical vapor deposition epitaxy, we grow a 2‐µm‐thick absorber on a (100) monocrystalline Si layer transfer seed on display glass and achieve 6.5% efficiency with an open circuit voltage (VOC) of 586 mV without light‐trapping features. This device enables the evaluation of seed layers on display glass. Using polycrystalline seeds formed from amorphous silicon by laser‐induced mixed phase solidification (MPS) and electron beam crystallization, we demonstrate 2.9%, 476 mV (MPS) and 4.1%, 551 mV (electron beam crystallization) solar cells. Grain boundaries likely limit the solar cell grown on the MPS seed layer, and we establish an upper bound for the grain boundary recombination velocity (SGB) of 1.6x104 cm/s. Copyright © 2014 John Wiley & Sons, Ltd.

Thin-film silicon-based quadruple junction solar cells approaching 20% conversion efficiency

Thin-film silicon-based solar cells are a well-established photovoltaic (PV) technology. The best reported initial and stabilized conversion efficiency is 16.3% and 13.4%, respectively. Thin-film silicon PV technology needs to achieve initial conversion efficiency approaching 20% in order to stay competitive with other PV technologies. The multi-junction approach is regarded as the main strategy for improving cells efficiency. In this contribution, we study thin-film silicon-based solar cells based on a quadruple junction device and discuss their potential for achieving a high efficiency. We carried out optical modelling of this novel device structure using state-of-the-art materials and light management techniques. We demonstrate a quadruple junction cell with simulated photo-generated current density of 8.7mA/cm2 in current-matching condition and potential initial conversion efficiency of 19.6%. A significant spectral overlap is observed between the component cells that makes the design of the current-matched device complex. We can control the spectral overlap by employing band-gap engineering of absorber layers and design an improved current-matched quadruple junction solar cell with potential initial conversion efficiency equal to 19.8%.

Experimental Demonstration of Quasi-resonant Absorption in Silicon Thin Films for Enhanced Solar Light Trapping

We experimentally demonstrate that the addition of partial lattice disorder to a thin-film micro-crystalline silicon photonic crystal results in the controlled spectral broadening of its absorption peaks to form quasi resonances; increasing light trapping over a wide bandwidth while also reducing sensitivity to the angle of incident radiation. Accurate computational simulations are used to design the active-layer photonic crystal so as to maximize the number of its absorption resonances over the broadband interval where micro-crystalline silicon is weakly absorbing before lattice disorder augmented with fabrication-induced imperfections are applied to further boost performance. Such a design strategy may find practical use for increasing the efficiency of thin-film silicon photovoltaics.

Laser Texturing of Surfaces in Thin-Film Silicon Photovoltaics - A Comparison of Potential Processes

Laser Texturing of Surfaces in Thin-Film Silicon Photovoltaics - A Comparison of Potential Processes

Correlations Between Mapping Spectroscopic Ellipsometry Results and Solar Cell Performance for Evaluations of Nonuniformity in Thin-Film Silicon Photovoltaics

An understanding of the relationship between materials property and thin-film solar cell performance variations over large areas is of interest for evaluating the impact of macroscopic nonuniformities in scale-up from laboratory cells to production modules. In this study, we have spatially correlated the properties of the hydrogenated silicon (Si:H) i- and p-layers-as mapped over a 13 cm×13 cm substrate area-with device performance parameters from an array of a-Si:H based n-i-p dot cells. To evaluate materials and device nonuniformities, a 16 × 16 array of dot cells has been fabricated over the substrate area, and this same area has been mapped by spectroscopic ellipsometry (SE).Analysis of the SE data over the full area provides maps of i-layer thickness and band gap, p-layer thickness and band gap, and p-layer surface roughness thickness for the n-i-p solar cell structure. The mapped values adjacent to the devices have been correlated with photovoltaic (PV) device performance parameters. When sufficient nonuniformity exists, these correlations enable optimization based on specific values of the fundamental properties. Alternatively, if the optimum set of properties has been identified, the impact of deviations due to macroscopic uniformities can be evaluated.

Ultralight-Trapping Filters With Volume Reflection Holograms

Light trapping is a useful approach for increasing the absorption of thin film photovoltaic (PV) cells. Simple light trapping can be achieved by incorporating a scattering layer on the top and bottom surface of cells and can increase absorption by a factor of 4n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Recently, ultralight trapping using Rugate and 1-D photonic bandgap filters have been proposed to increase light trapping by a factor of 4n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /sin <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> θ, where θ is half of the acceptance angle. In this paper, we present the design of a holographic ultralight trapping filter. The holographic filter can be implemented in large areas at a low cost, which makes it scalable for PV applications. A design is presented that increases the optical path length for near bandgap wavelengths in a thin-film silicon PV cell. The optical path length enhancement is converted to electrical output using the PC-1D simulation software. The short-circuit current for a 10-μm-thick silicon PV cell increases by nearly 14.7% relative to a cell without light trapping.

Amorphous and nanocrystalline silicon thin film photovoltaic technology on flexible substrates

This paper reviews our thin film silicon-based photovoltaic (PV) technology, including material and device studies as well as roll-to-roll manufacturing on a flexible substrate. Our current thin film silicon PV products are made with hydrogenated amorphous silicon (a-Si:H) and amorphous silicon germanium (a-SiGe:H) alloys. The advantages of a-Si:H-based technology are low cost, capability of large scale manufacturing, abundance of raw materials, and no environmental concerns. One disadvantage of a-Si:H PV technology is lower energy conversion efficiency than solar panels made of crystalline and polycrystalline silicon and compound crystal thin film semiconductors. Significant efforts have been made to improve efficiency. First, a-Si:H and a-SiGe:H material quality has been improved by optimizing deposition conditions, especially using high hydrogen dilution to deposit the amorphous materials close to the amorphous/nanocrystalline transition. Second, cell efficiency has been improved by engineering the device structure, such as bandgap profiling. In order to use the solar spectrum effectively, multijunction structures that incorporate a-SiGe:H in the middle and bottom cells have been used. The authors achieved record high solar cell efficiency with an a-Si:H/a-SiGe:H/a-SiGe:H triple-junction structure. Using the same structure, we fabricated solar laminates on flexible stainless steel coils with roll-to-roll production systems. Our current product has a stable aperture area efficiency of 8.2%. In recent years, hydrogenated nanocrystalline silicon (nc-Si:H) has emerged as a potential replacement for the a-SiGe:H bottom cell in multijunction structures. The authors have conducted a great deal of research and development of a-Si:H- and nc-Si:H-based multijunction PV technology. The authors have significantly improved the efficiency of a-Si:H and nc-Si:H multijunction solar cells and modules by optimizing the nc-Si:H material quality and device structure. The authors achieved an initial active-area (∼0.25 cm2) solar cell efficiency of 16.3% using an a-Si:H/a-SiGe:H/nc-Si:H triple-junction structure and an initial aperture-area module (∼400 cm2) efficiency of 12.0% and a stable aperture-area module (∼800 cm2) efficiency of 11.3% using an a-Si:H/nc-Si:H/nc-Si:H triple-junction structure. The authors expect to launch a new a-Si:H/nc-Si:H/nc-Si:H triple-junction product in near future with much higher efficiency than the current product.

Preface: Phys. Status Solidi C 10/2011

AbstractThe Third International Workshop on thin film silicon solar cells (IWTFSSC‐3) was held on 11–14 October 2010 at ANA Hotel Nagasaki Gloverhill in Nagasaki, Japan (the first workshop was in Nara, Japan in 2007 and the second one in Berlin, Germany in 2009). This workshop mainly consists of invited talks and panel discussion on the present status and future prospects of thin film silicon photovoltaics (PV) technologies. The 50 participants include internationally most renowned experts. 50 reports were presented including 20 invited talks. Among these reports, 13 papers were selected to be published in this special issue.Driven by an increasing demand for PV, a shortage of crystalline silicon and the availability of turn‐key production lines, thin film silicon solar cells have been attracting increasing attention over the past few years. Many companies have invested in mass production lines for a‐Si and a‐Si/μc‐Si solar modules. A large number of these companies are still in the ramp‐up phase, or even before.Despite impressive growth of the thin film Si manufacturing capacity, many technological issues remain of importance. These include high deposition rate processes, large area uniformity, optical confinement, or laser scribing. To stay ahead of competing technologies, it will be important to address more fundamental and longer‐term issues as well, such as photo degradation of a‐Si, very high current cells, triple cells, new structures, or advanced transparent conductive oxides (TCOs).It is the aim of this workshop to address these and other topics, and to discuss them in an informal atmosphere with other experts. All participants vigorously exchanged their ideas leading to significant progress in important issues in thin film silicon solar cells.Thanks to the organizers and participants, there was an excellent blend of research reports from industry and academia and research reports worldwide (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Modeling of light scattering properties from surface profile in thin-film solar cells by Fourier transform techniques

The optical properties of textured surfaces in the micro and nanometer range are of interest in manifold topics, such as thin-film silicon photovoltaics. Light scattering models, which are based on Fourier transform techniques, are applied to calculate both, the angularly resolved scattering and the haze. Therein, topography, measured by atomic force microscopy, and the refractive index are used as input data. In this study, these models are applied to zinc oxide/air interfaces and to zinc oxide/hydrogenated amorphous silicon interfaces. Results obtained from zinc oxide/air interfaces are compared to the measured scattering properties.

Real time spectroscopic ellipsometry of Ag/ZnO and Al/ZnO interfaces for back-reflectors in thin film Si:H photovoltaics

Real time spectroscopic ellipsometry (RTSE) has been applied to analyze the optical characteristics of Ag/ZnO and Al/ZnO interfaces used in back-reflector (BR) structures for thin film silicon photovoltaics. The structures explored here are relevant to the substrate/BR/Si:H(n-i-p) solar cell configuration and consist of opaque Ag or Al films having controllable thicknesses of microscopic surface roughness, followed by a ZnO layer up to ~3000Å thick. The thicknesses of the final surface roughness layers on both Ag and Al have been varied by adjusting magnetron sputtering conditions in order to study the effects of metal film roughness on interface formation and interface optical properties. The primary interface loss mechanisms in reflection are found to be dissipation via absorption through localized plasmon modes for Ag/ZnO and through intraband and interband transitions intrinsic to metallic Al for Al/ZnO.

Thin Film Silicon Photovoltaic Technology – From Innovation to Commercialization

AbstractThe last decade has witnessed tremendous progress in the science and technology of thin film silicon (amorphous and nanocrystalline) photovoltaic. The shipment of solar panels using this technology was about 200 MW in 2009; based on announcement of new or expanded production capacity, the shipment is projected to grow ten-times in the next 3-5 years. The key factor that will determine the wide-scale acceptance of the products will be the cost of solar electricity achieved using this technology. Efficiency of solar modules and throughput of production equipment will play a key role. In this paper, we discuss our roadmap to improve the product efficiency and machine throughput.

PECVD in-situ growth of silicon quantum dots in silicon nitride from silane and nitrogen

Silicon nanostructures have interesting possible applications in new generation photovoltaics. The fabrication techniques usually involve a high-temperature post-deposition annealing. Here we report on the spontaneous growth of silicon quantum dots in silicon nitride films by plasma enhanced chemical vapour deposition (PECVD) using silane and nitrogen as reactant gas sources. The growth rate was kept low by working at low discharge power, and a low deposition temperature was selected (300 °C). This approach is particularly interesting because in principle it allows for use of low cost substrates and application of typical device structures adopted in thin film silicon photovoltaics. Photoluminescence and optical properties have been investigated. The evolution of the photoluminescence emission with nitrogen flow rate has been correlated to the change of the dot size. The effect of the strongly absorbing Si nanostructures in the silicon nitride matrix on the absorption properties has been investigated.

MW plasma enhanced CVD of intrinsic Si for thin film solar cells

ABSTRACTOur aim is the development of high-throughput production technology for high efficiency, amorphous and microcrystalline thin film silicon photovoltaics (PV) on flexible substrates. A roll-to-roll system is developed, with three deposition chambers for the continuous deposition of n-type, intrinsic and p-type Si. Novel MW sources for plasma enhanced chemical vapour deposition (PECVD) are introduced in the roll-to-roll coater as MW-PECVD combines good quality with large area, high rate deposition of intrinsic Si. A comparison is made between Raman and UV-reflection spectroscopy.