Ultrathin Solar Cells Research Articles

Plasmon-enhanced parabolic nanostructures for broadband absorption in ultra-thin crystalline Si solar cells.

Sub-wavelength plasmonic light trapping nanostructures are promising candidates for achieving enhanced broadband absorption in ultra-thin silicon (Si) solar cells. In this work, we use finite-difference time-domain (FDTD) simulations to demonstrate the light harvesting properties of periodic and parabola shaped Si nanostructures, decorated with metallic gold (Au) nanoparticles (NPs). The active medium of absorption is a 2 μm thick crystalline-silicon (c-Si), on top of which the parabolic nanotextures couple incident sunlight into guided modes. The parabola shape provides a graded refractive index profile and high diffraction efficiencies at higher order modes leading to excellent antireflection effects. The Au NPs scatter light into the Si layer and offer strong localized surface plasmon resonance (LSPR) resulting in broadband absorption with high conversion efficiency. For wavelengths (λ) ranging between 300 nm and 1600 nm, the structure is optimized for maximum absorption by adjusting the geometry and periodicity of the nanostructures and the size of the Au NPs. For parabola coated with 40 nm Au NPs, the average absorption enhancements are 7% (between λ = 300 nm and 1600 nm) and 28% (between λ = 800 nm and 1600 nm) when compared with bare parabola. Furthermore, device simulations show that the proposed solar cell can achieve a power conversion efficiency (PCE) as high as 21.39%, paving the way for the next generation of highly efficient, ultra-thin and low-cost Si solar cells.

Construction of ultrathin perovskite solar cells by different periodic structures

Construction of ultrathin perovskite solar cells by different periodic structures

Eco-friendly and ultrathin solar cells featuring nanocrystals: advances and perspectives

A comprehensive and critical review of the emerging eco-friendly solar cells such as AgBiS2 is presented with the goal of further advancing the photovoltaic performance and stability.

Realistic Multidimensional Optoelectrical Modeling Guide for Copper Indium Gallium Diselenide Solar Cells

Herein, an optoelectrical model is presented for copper indium gallium diselenide (CIGSe) solar cells in COMSOL Multiphysics, capable of multidimensional simulations, and it is applied to ultrathin (500 nm absorber thickness) solar cells. First, the modeling approach is shown. Special attention is paid to back contact materials, interface states, and defect application and their impact on the current–voltage (J–V) characteristics. To address whether the back contact is Schottky or Ohmic, the influence of the Schottky barrier height, recombination velocity, and interface states is shown. Then, the additional application of an acceptor defect gradient at the absorber back and a donor defect density distribution at the p–n junction is investigated. The results of these parameter adjustments are discussed, and the trends are shown to enable fast fitting of experimental J–V curves. Finally, the results are compared to the experimental J–V curves for indium tin oxide and Mo back contact, and challenges encountered are discussed while fitting. The optoelectrical model for CIGSe solar cells, established in two dimensions here, paves the way for comprehensively describing 2D and 3D solar cell structures, e.g., nanotextured or microsolar cells, as well as for considering different absorber thicknesses.

Cataloguing MoSi2N4 and WSi2N4 van der Waals Heterostructures: An Exceptional Material Platform for Excitonic Solar Cell Applications

Abstract2D materials van der Waals heterostructures (vdWHs) provide a revolutionary route toward high‐performance solar energy conversion devices beyond the conventional silicon‐based pn junction solar cells. Despite tremendous research progress accomplished in recent years, the searches of vdWHs with exceptional excitonic solar cell conversion efficiency and optical properties remain an open theoretical and experimental quest. Here, this study shows that the vdWH family composed of MoSi2N4 and WSi2N4 monolayers provides a compelling material platform for developing high‐performance ultrathin excitonic solar cells and photonics devices. Using first‐principle calculations, 51 types of MoSi2N4 and WSi2N4‐based [(Mo,W)Si2N4] vdWHs composed of various metallic, semimetallic, semiconducting, insulating, and topological 2D materials are constructed and classified. Intriguingly, MoSi2N4/(InSe, WSe2) are identified as Type II vdWHs with exceptional excitonic solar cell power conversion efficiency reaching well over 20%, which are competitive to state‐of‐the‐art silicon solar cells. The (Mo,W)Si2N4 vdWH family exhibits strong optical absorption in both the visible and UV regimes. Exceedingly large peak UV absorptions over 40%, approaching the maximum absorption limit of a freestanding 2D material, can be achieved in (Mo,W)Si2N4/α2‐(Mo,W)Ge2P4 vdWHs. The findings unravel the enormous potential of (Mo,W)Si2N4 vdWHs in designing ultimately compact excitonic solar cell device technology.

Seed Layer Optimisation for Ultra-Thin Sb2Se3 Solar Cells on TiO2 by Vapour Transport Deposition.

Antimony selenide (Sb2Se3) material has drawn considerable attention as an Earth-abundant and non-toxic photovoltaic absorber. The power conversion efficiency of Sb2Se3-based solar cells increased from less than 2% to over 10% in a decade. Different deposition methods were implemented to synthesize Sb2Se3 thin films, and various device structures were tested. In search of a more environmentally friendly device composition, the common CdS buffer layer is being replaced with oxides. It was identified that on oxide substrates such as TiO2 using vacuum-based close-space deposition methods, an intermediate deposition step was required to produce high-quality thin films. However, little or no investigation was carried out using another very successful vacuum deposition approach in Sb2Se3 technology called vapour transport deposition (VTD). In this work, we present optimized VTD process conditions to achieve compact, pinhole-free, ultra-thin (<400 nm) Sb2Se3 absorber layers. Three process steps were designed to first deposit the seed layer, then anneal it and, at the final stage, deposit a complete Sb2Se3 absorber. Fabricated solar cells using absorbers as thin as 400 nm generated a short-circuit current density over 30 mA/cm2, which demonstrates both the very high absorption capabilities of Sb2Se3 material and the prospects for ultra-thin solar cell application.

Efficiency enhancement of ultrathin CIGS solar cells by optimal bandgap grading. Part II: finite-difference algorithm and double-layer antireflection coatings.

In Part I [Appl. Opt.58, 6067 (2019)APOPAI003-693510.1364/AO.58.006067], we used a coupled optoelectronic model to optimize a thin-film C u I n 1-ξ G a ξ S e 2 (CIGS) solar cell with a graded-bandgap photon-absorbing layer and a periodically corrugated backreflector. The increase in efficiency due to the periodic corrugation was found to be tiny and that, too, only for very thin CIGS layers. Also, it was predicted that linear bandgap-grading enhances the efficiency of the CIGS solar cells. However, a significant improvement in solar cell efficiency was found using a nonlinearly (sinusoidally) graded-bandgap CIGS photon-absorbing layer. The optoelectronic model comprised two submodels: optical and electrical. The electrical submodel applied the hybridizable discontinuous Galerkin (HDG) scheme directly to equations for the drift and diffusion of charge carriers. As our HDG scheme sometimes fails due to negative carrier densities arising during the solution process, we devised a new, to the best of our knowledge, computational scheme using the finite-difference method, which also reduces the overall computational cost of optimization. An unfortunate normalization error in the electrical submodel in Part I came to light. This normalization error did not change the overall conclusions reported in Part I; however, some specifics did change. The new algorithm for the electrical submodel is reported here along with updated numerical results. We re-optimized the solar cells containing a CIGS photon-absorbing layer with either (i)a homogeneous bandgap, (ii)a linearly graded bandgap, or (iii)a nonlinearly graded bandgap. Considering the meager increase in efficiency with the periodic corrugation and additional complexity in the fabrication process, we opted for a flat backreflector. The new algorithm is significantly faster than the previous algorithm. Our new results confirm efficiency enhancement of 84% (resp. 63%) when the thickness of the CIGS layer is 600nm (resp. 2200nm), similarly to Part I. A hundredfold concentration of sunlight can increase the efficiency by an additional 27%. Finally, the currently used 110-nm-thick layer of M g F 2 performs almost as well as optimal single- and double-layer antireflection coatings.

Radiation effects in ultra-thin GaAs solar cells

Ultra-thin solar cells are of significant interest for use in space due to their intrinsic radiation tolerance, which may allow them to be used in particularly harsh radiation environments, where thicker cells would degrade rapidly and enable reduction in cover glass thickness to reduce launch mass. In this study, devices with an 80 nm GaAs absorber layer were irradiated with 3 MeV protons. It is shown that integrated light management in these ultra-thin devices offers enhanced efficiency, in addition to extended lifetime through radiation resilience. Time-resolved cathodoluminescence is employed to map the introduction of radiation-induced defects with increasing proton fluence and characterize a decrease in carrier lifetime from 198 ± 5 ps pre-radiation to 6.2±0.6 ps, after irradiation to 2×1014 cm−2 fluence. Despite the substantial reduction in carrier lifetime, short-circuit current does not degrade up to a proton fluence of 1 × 1015 cm−2, beyond which a collapse in short-circuit current is observed. This exposure correlates with the point at which the carrier lifetime, extrapolated from cathodoluminescence, becomes comparable to the transit time for carriers to cross the ultra-thin device. Variation in current–voltage behavior with carrier lifetime and fluence shows that the recombination statistics are similar to those of a Shockley–Read–Hall single deep-level trap model, but that bimolecular recombination does not fully describe the observed behavior. An implication of these highly radiation tolerant cells for space power systems is shown to offer significant savings in cover glass mass, compared with a thicker cell.

Simulation of photon recycling in ultra-thin solar cells

A comprehensive quantum-kinetic simulation framework considering both the optical confinement and the electronic effects of finite size and strong built-in fields is introduced to assess the impact of photon recycling on the photovoltaic performance of ultra-thin absorber solar cells. The radiative recombination accounts for the actual photon density of states that is modified by cavity effects and plasmonic resonances, and via coupling to a quantum transport formalism, the impact of photon recycling is propagated from rigorous wave optical simulation of secondary photogeneration directly into a modification of the current–voltage characteristics of the full photovoltaic device. The self-consistent microscopic treatment of the interacting electronic and optical degrees of freedom in a functional device context elucidates the impact on photovoltaic performance of nanoscale device design in terms of band profiles and contact layers by revealing their effect on the radiative rates and currents. As an example, plasmonic losses related to metallic reflectors are identified in both, emission and re-absorption, and partial mitigation is achieved via dielectric passivation or detaching of the reflector.

Performance enhancement of CZTS-based solar cells with tungsten disulfide as a new buffer layer

2D layered Transition Metal Dichalcogenide materials (TMDCs) have shown promising potential for ultra-thin photovoltaic and solar cells applications owing to their outstanding photon absorption and electrical and optoelectronics features. This paper intended to discuss a numerical exploration of the CZTS based solar cells employing the solar cell capacitance simulator (SCAPS-1D), using a novel non-toxic n-type WS2 TMDCs as a buffer layer. The cell parameters, such as the thickness and defect density of the CZTS absorber, are optimized. Then, the impact of the energy bandgap (Eg) and the back contact work function of the WS2 buffer layer on cell performance is investigated. An optimized Eg of 2.2 eV is declared. The results refer to the promoting conduction band alignments at the interface of the buffer absorber (i.e., WS2/CZTS). Further, we have studied the photovoltaic cell performance versus the defect level of the WS2 buffer layer. It was resolved that deep defect levels exceeding 1 × 1018 cm−3 degrade cell efficiency. The results show an optimized power conversion efficiency of about 26.81% with Voc = 1.17 V, Jsc = 27.7 mA/cm2, and FF = 83.66%. The simulation was further analyzed and discussed at various operating temperatures. The novel device architecture using WS2 as a buffer layer might encourage the fabrication of non-toxic CZTS solar cells.

Role of metallic nanoparticles in the optoelectronic performance enhancement of InP ultrathin film solar cell

III-V material-based ultrathin Solar Cells (SCs) garnered a great deal of interest due to their benefits such as efficient charge transport, recycling of photons, adaptability, and material usage but suffer from low optical absorption due to thicker active material. In order to increase the optical absorption in the ultra-thin SC, metal nanoparticles (MNPs) are employed that scatter the incident light in the absorber layer resulting in higher optical absorption with the reduced requirement of active material. The role of MNPs in the efficiency improvement of InP SCs has not yet been explored. Therefore, in this paper, we have investigated the impact of plasmonic MNPs of different materials such as gold (Au), silver (Ag) and aluminium (Al) placed on the top of ITO coated 280 nm ultra-thin InP SC with FDTD simulations, which employ the surface plasmon resonance (SPR) to increase the optical absorption by tuning the dimensions of the MNPs. The thickness of InP thin-film and an anti-reflective coating of ITO are optimized to achieve maximum absorption. In addition, the diameter and period of Au, Ag, and Al MNPs are also optimized to achieve higher optical Jsc, and results show that Au nanoparticle with diameter of 50 nm and period of 100 nm shows higher Jsc when compared to Ag and Al nanoparticles of optimized diameter. The device analysis shows the Au nanoparticles placed on the top surface of ITO coated InP ultrathin SC with a power conversion efficiency (PCE) of 22.3% outperform the Ag NPs and Al NPs ITO coated InP ultrathin SC and ITO/InP ultrathin SC without MNPs.

High broadband light absorption in ultrathin MoS2 homojunction solar cells.

Transition metal dichalcogenides (TMDCs) have been proposed as light absorber materials for ultrathin solar cells. These materials are characterized by their strong light-matter interaction and the possibility to be assembled into devices at room temperature. Here, we model the optical absorptance of an ultrathin MoS2 absorber embedded in different designs of a 1D optical cavity. We find that up to 87% of the photons contained in the 300-700 nm range of the AM1.5G spectrum can be absorbed employing MoS2 absorbers as thin as 10 nm sandwiched between a h-BN top layer and an optically thick Ag reflector. An h-BN/MoS2/h-BN/Ag cavity produces 0.89 average absorptance for a 57-nm-thick MoS2 slab and it also maximizes the absorption of extremely thin absorbers, between 1 and 9 nm. We also model a possible large-scale device on a glass substrate combined with indium-tin oxide (ITO) whose absorptance is comparable to the other presented structures. The high broadband absorption in these light-trapping structures is caused by the amplification of the zeroth Fabry-Perot interference mode. This study demonstrates that light absorption in ultrathin solar cells based on nanometric TMDC absorbers can compete with conventional photovoltaic technology and provides different simple optical designs to choose from depending on the electronic characteristics of the TMDC junction.

Optical absorption enhancement in ultrathin chalcopyrite solar cells with Ag reflective back contact

The optical performance of ultrathin solar cells based on chalcopyrite CuInS2 absorber has been studied, simulating the total absorption as a function of the absorber thickness with and without Ag reflective back contact. The structure chosen is ZnO:Al/SnS2/CuInS2/Ag/Mo/glass, using for the simulation the experimental data extracted from the layers prepared in our laboratory by evaporation (CuInS2 and SnS2) and sputtering (ZnO:Al, Ag and Mo). The main purpose has been to apply realistic input parameters (refractive index and extinction coefficient extracted from transmittance and reflectance measurements for each layer) to simulate and analyze the optical behavior of the entire device. It is found that the overall absorption of the cell with 0.2 μm-thick CuInS2 and 60 nm-thick Ag is the same as that obtained for 0.4 μm-thick CuInS2 without Ag layer. Thus, the incorporation of Ag reflective contact allows reducing the absorber layer thickness and therefore the time and cost of manufacturing chalcopyrite cells, being especially relevant for absorber thicknesses below 0.4 μm.

Enhanced light absorption of kinked nanowire arrays for high-performance solar cells

A kinked InP nanowire array solar cell architecture is proposed for high-performance solar cells. Coupled three-dimensional optoelectronic simulations are performed to investigate the optical absorption and photovoltaic conversion properties. The results show that the kinked morphology significantly enhances the absorption by increasing the optical path, exciting more resonance modes, and reducing the transmission into the substrate. Moreover, the kinked morphology also increases the absorption in the intrinsic region by suppressing the absorption loss in the top doped region. For short nanowires with a total length of 1–1.5 μm, the kinked structures exhibit remarkable efficiency exceeding 14%, significantly higher than the vertical nanowires. Nanowires with different kinked angles are studied, and a moderate kinked angle is beneficial for obtaining optimal performance. This work demonstrates the potential of kinked nanowires in ultra-thin low-cost high-efficiency solar cells.

Theoretical modeling and ultra-thin design for multi-junction solar cells with a light-trapping front surface and its application to InGaP/GaAs/InGaAs 3-junction.

Light-trapping design is a good strategy to obtain ultra-thin solar cells without sacrificing conversion efficiency. If applied to III-V compound multi-junction solar cells (MJSCs), it not only can greatly reduce the cell cost and weight, but also improve its radiation tolerance when operating in space. This paper formulates all subcell absorptance in an arbitrary N-junction solar cell with an ideal front textured surface and perfect rear mirror, including the effects of complex absorption and luminescence coupling in the stack. Taking the well-known InGaP/GaAs/InGaAs triple-junction solar cell (3J) for instance, the ultra-thin design and the conversion efficiency both in radiative limit and that with subcell internal radiative efficiency below-unity are predicted. Our results show that such front-textured 3J with top-subcell thickness varying from 200 to 500 nm can enhance light absorption so significantly that more than 28% of top-subcell, 56% of middle-subcell, and 90% of bottom-subcell thickness will be cut down when compared with the smooth-surfaced 3J. Typically, (350 nm, 315 nm, 28 nm) is recommended as the optimal design for the front-textured 3J with an experimental efficiency of over 38%. For the same benchmarks on photocurrent of 15.1 mA/cm2 or detailed balance limit of 44%, the minimum total thickness (all subcells only) in the front-textured 3J is only 1453 nm, that is even 71% of that in the rear-textured 3J, quantitatively revealing front texturization has a greater potential for material cut-down than rear texturization. Finally, the impacts of non-ideal scattering texturization on cell performance and ultra-thin design are also discussed. This work provides theoretical guidance for experimental studies on ultra-thin and high-efficient MJSCs with various light-trapping strategies.

Integration of body-mounted ultrasoft organic solar cell on cyborg insects with intact mobility

Cyborg insects have been proposed for applications such as urban search and rescue. Body-mounted energy-harvesting devices are critical for expanding the range of activity and functionality of cyborg insects. However, their power outputs are limited to less than 1 mW, which is considerably lower than those required for wireless locomotion control. The area and load of the energy harvesting device considerably impair the mobility of tiny robots. Here, we describe the integration of an ultrasoft organic solar cell module on cyborg insects that preserves their motion abilities. Our quantified system design strategy, developed using a combination of ultrathin film electronics and an adhesive–nonadhesive interleaving structure to perform basic insect motion, successfully achieved the fundamental locomotion of traversing and self-righting. The body-mounted ultrathin organic solar cell module achieves a power output of 17.2 mW. We demonstrate its feasibility by displaying the recharging wireless locomotion control of cyborg insects.

Transient performance modelling of ultra-thin Sn-based perovskite solar cells based on electrode contact design to improve thermal stability

Transient performance modelling of ultra-thin Sn-based perovskite solar cells based on electrode contact design to improve thermal stability

Titanium‐Oxide‐Based Electron‐Selective Contact for Ultrathin Germanium Quantum Well Solar Cell

In solar cells with an optical cavity as a light trapping mechanism, parasitic absorption is among the main detrimental optical losses. One approach to reducing these losses is the implementation of charge carrier‐selective contacts with wide bandgaps using thin metal oxides like titanium oxide (TiOx). Herein, it is proved that TiOx is a suitable alternative for lossy n‐doped hydrogenated amorphous silicon (n a‐Si:H) as electron selective contact in ultrathin solar cells based on intrinsic hydrogenated amorphous germanium (a‐Ge:H). The integration of the TiOx layer leads to an improved photocurrent generation in the blue light wavelengths. Furthermore, a substantial extraction of charge carriers is demonstrated from the a‐Ge:H quantum well nanoabsorber embedded between intrinsic a‐Si barrier layers. However, the substitution of n a‐Si:H by TiOx results in limited photovoltaic performance due to a lower open‐circuit voltage. This effect is analyzed via electrical simulation considering a variation in the electron affinity and the doping of TiOx as well as the defect density in the silicon buffer. Moreover, the TiOx‐based solar cell exhibits improved light transmittance when the opaque back contact is omitted, which is beneficial for semi‐transparent applications.

Ultrathin Film Amorphous Silicon Solar Cell Performance using Rigorous Coupled Wave Analysis Method

The issues related to global energy needs and environmental safeties as well as health crisis are some of the major challenges faced by the human, which make us to generate new pollution-free and sustainable energy sources. For that the optical functional nanostructures can be manipulated the confined light at the nanoscale level. These characteristics are emerging and leading candidate for the solar energy conversion. The combination of photonic (dielectric) and plasmonic (metallic) nanostructures are responsible for the development of better optical performance in solar cells. Here, the enhancement of light trapping within the thin active region is the primary goal. In this work, we have studied the influence of front-ITO (rectangular) and back-Ag (triangular) nanogratings were incorporated with ultrathin film amorphous silicon (a-Si) solar cell by using rigorous coupled wave analysis (RCWA) method. The improvement of light absorption, scattering (large angle), diffraction and field distributions (TE/TM) were demonstrated by the addition of single and dual nanogratings structures. Significantly, the plasmonic (noble metal) nanogratings are located at the bottom of the cell structure as a backside reflector which is helpful for the omni-directional reflection and increased the path length (life time) of the photons due to that the collection of the charge carriers were enhanced. Further, the proposed solar cell structure has optimized and compared to a back-Ag, front-ITO and dual nanogratings based ultrathin film amorphous silicon solar cell. Finally, the obtained results were evidenced for the assistance of photonic and plasmonic modes and achieved the highest current density (Jsc) of 23.82 mA/cm2(TE) and 22.75 mA/cm2 (TM) with in 50 nm thin active layers by integration of (dual) cell structures.

Mechanically and Ultraviolet Light Stable Ultrathin Organic Solar Cell via Semi-Embedding Silver Nanowires in a Hydrogen Bonds-Based Polyimide.

Ultrathin organic solar cells (OSCs) with both high power conversion efficiency (PCE) and operational stability are of great significance for the industrial applications but still challenging. Here, a polyimide (PI) substrate for high-performance and stable ultrathin OSCs, which is physically crosslinked via strong hydrogen bonds (denoted as HB-PI) to enhance the mechanical, thermal, solvent-resistant, and UV filtering properties (with a cut-off wavelength of 376nm), is synthesized. An ultrathin flexible transparent composite electrode (FTCE, ≈7µm) is fabricated via semi-embedding AgNWs in the HB-PI substrate. The FTCE possesses excellent optoelectronic property, smooth surface, and high mechanical stability simultaneously. Based on this FTCE, an ultrathin OSC is constructed with a PCE of 13.52% (average of 13.22%). Moreover, the ultrathin OSC shows outstanding mechanical stability (PCE decreased by less than 4% after 1000 bending cycles at a small bending radius of 0.5mm) and superior UV light stability (no evident PCE degradation after irradiation under UV light for 10h). This work will provide a new avenue for fabricating high-performance and stable ultrathin OSCs.