Thin-film Tandem Solar Cells Research Articles

Full optoelectronic simulation of all antimony chalcogenide thin film tandem solar cell: Design routes from 4-T to 2-T configuration

Antimony chalcogenide, as a newcomer to light harvesting materials, is regarded as an auspicious contender for incorporation as a photoactive layer in thin film tandem solar cells (TFTSCs). The current study introduces the design of all-antimony chalcogenide TFTSC comprised of an Sb2S3 (1.7 eV) front subcell and an Sb2Se3 (1.2 eV) rear subcell. The challenges to migrating from four-terminal (4-T) to two-terminal (2-T) designs are highlighted and possible solutions are proposed. To commence, a calibration procedure for the two subcells is conducted in alignment with experimental investigations. The benchmarked solar cells yield a power conversion efficiency (PCE) of 8.08 % for the upper subcell and 10.58 % for the lower subcell. Subsequently, upon integration of both subcells within the initial 4-T Sb2S3/Sb2Se3 TFTSC, the resultant PV cell attains a PCE of 12.27 %. Before transitioning it to a more efficient 2T tandem configuration, we explore alternative inorganic HTL materials to the Spiro-OMeTAD HTL to overcome its practical considerations. Cu2O is found to be the best HTL alternative to be included for both subcells. Upon stacking into the tandem structure, the combined cell exhibited an efficiency of 15.68 % and a notable Jsc of 16.23 mA/cm2. To further enhance the tandem performance, the device structure is optimized by engineering the CBO of two sub-cells and employing a double ETL design for the front sub-cell. At the considered current matching criterion, the tandem device PCE and Jsc are boosted to 27.86 % and 17.60 mA/cm2, respectively. Based on this full optoelectronic analysis, developed in the Silvaco TCAD environment, a 2-T all antimony chalcogenide tandem configuration can be realized and optimized, paving the way for future experimental endeavors.

Comprehensive design and analysis of thin film Sb2S3/CIGS tandem solar cell: TCAD simulation approach

This research presents a design and analysis of a tandem solar cell, combining thin film wide bandgap Sb2S3 (1.72 eV) and narrow bandgap CIGS (1.15 eV) for the top and bottom sub-cells, respectively. The integration of all thin film layers enhances flexibility, rendering the tandem solar cell suitable for applications such as wearable electronics. To optimize the power conversion efficiency (PCE) of the tandem solar device, advanced technology computer-aided design (TCAD) simulation tools are employed to estimate loss mechanisms and fine-tune parameters for each layer. An experimentally validated optoelectronic model is introduced, calibrated and validated against fabricated reference solar cells for the individual top and bottom cells. The calibrated model is then utilized to propose optimization routines for the Sb2S3/CIGS tandem solar cell. The initial tandem cell exhibits a J SC of 15.72 mA cm−2 and a PCE of 15.36%. The efficiency drop in the tandem configuration is identified primarily in the top cell. A systematic optimization process for the top cell is initiated, exploring various configurations, including HTL-free and ETL-free setups. Moreover, an np homojunction structure for the top cell is proposed. Optimization routines are applied that involve determining optimal thickness and doping concentration of the n-layer, investigating the effect of p-layer doping concentration, and exploring the influence of the work function of the front contact. As a result, the tandem cell efficiency is significantly improved to 23.33% at the current matching point (CMP), with a J SC of 17.15 mA cm−2. The findings contribute to the advancement of thin-film tandem solar cell technology, showcasing its potential for efficient and flexible photovoltaic applications.

Optimization of all-polymer/Sb2Se3 tandem solar cells for enhanced efficiency: a comprehensive TCAD modeling approach

Abstract This paper introduces a novel tandem configuration, utilizing an all-thin film all-polymer solar cell (all-PSC) with a wide bandgap of 1.76 eV for the front cell and Sb2Se3 with a narrow bandgap of 1.2 eV for the bottom cell. The design of this tandem is performed by comprehensive optoelectronic TCAD tools, essential for optimizing parameters across multiple layers to reach maximum power conversion efficiency (PCE). Experimental validation of models is conducted through calibration and validation against fabricated reference all-polymer and Sb2Se3 solar cells, yielding calibrated PCEs of approximately 10.1% and 10.5%, respectively. Subsequently, validated simulation models for both top and rear cells are utilized to design a 2-T all-polymer/Sb2Se3 tandem cell, which initially achieves a PCE of 10.91%. Through systematic optimization steps, including interface engineering and homojunction structure design, a remarkable PCE of 24.24% is achieved at the current matching point, showcasing the potential of our proposed tandem solar cell design. This study represents a significant advancement in the field of thin-film tandem solar cells, offering promising avenues for efficient and cost-effective photovoltaic technologies, particularly in applications requiring flexibility.

Opportunities and challenges in perovskite-organic thin-film tandem solar cells.

Efficiency is paramount in enhancing the performance and cost-effectiveness of solar cells. Recent advancements in single-junction perovskite solar cells (PSCs) have yielded an impressive efficiency of 26.1%, nearing their theoretical limit. Meanwhile, multi-junction tandem solar cells exhibit a remarkable efficiency potential exceeding 42%, surpassing the 33% limit of single-junction cells, thereby opening avenues for ultra-high-efficiency solar cells. Tandem solar cells (TSCs) represent a groundbreaking photovoltaic technology, offering high efficiency, low cost, and a simple fabrication process. Among various TSCs, perovskite-organic TSCs (PO TSCs) are particularly promising due to their ability to leverage the complementary strengths of PSCs and organic solar cells (OSCs). PO TSCs are poised to outperform existing TSCs in terms of device performance, manufacturing cost, and diverse applications. The introduction of Y6-series non-fullerene acceptors (NFAs) over the past three years has significantly advanced the development of OSCs, leading to remarkable progress in PO TSCs. This paper commences by elucidating the advantages and potential of OSCs as bottom sub-cells in PO TSCs, followed by an in-depth review of mainstream interconnection layer (ICL) design. It then addresses key challenges in wide bandgap PSCs, including phase segregation, photovoltage loss, energy loss, and long-term stability. The paper concludes by examining critical factors influencing the future development of PO TSCs.

Investigation of Polymer/Si Thin Film Tandem Solar Cell Using TCAD Numerical Simulation.

The current study introduces a two-terminal (2T) thin-film tandem solar cell (TSC) comprised of a polymer-based top sub cell and a thin crystalline silicon (c-Si) bottom sub cell. The photoactive layer of the top sub cell is a blend of PDTBTBz-2F as a polymer donor and PC71BM as a fullerene acceptor. Initially, a calibration of the two sub cells is carried out against experimental studies, providing a power conversion efficiency (PCE) of 9.88% for the top sub cell and 14.26% for the bottom sub cell. Upon incorporating both sub cells in a polymer/Si TSC, the resulting cell shows a PCE of 20.45% and a short circuit current density (Jsc) of 13.40 mA/cm2. Then, we optimize the tandem performance by controlling the valence band offset (VBO) of the polymer top cell. Furthermore, we investigate the impact of varying the top absorber defect density and the thicknesses of both absorber layers in an attempt to obtain the maximum obtainable PCE. After optimizing the tandem cell and at the designed current matching condition, the Jsc and PCE of the tandem cell are improved to 16.43 mA/cm2 and 28.41%, respectively. Based on this TCAD simulation study, a tandem configuration established from an all thin-film model may be feasible for wearable electronics applications. All simulations utilize the Silvaco Atlas package where the cells are subjected to standard one Sun (AM1.5G, 1000 W/m2) spectrum illumination.

Optical Simulation Study of Perovskite/CIGS Tandem Solar Cells With Reduced Graphene Oxide Layers

Tandem solar cells present a promising solution to overcome the Schottky–Queisser efficiency limit of single-junction solar cells. In this article, an all–thin-film tandem solar cell based on perovskite (PK) top cell and chalcopyrite Cu (In, Ga) Se2 (CIGS) bottom cell is researched. Device optical simulations are validated on the top and bottom cells and employed for the analysis of PK/CIGS tandem cells. In particular, the optical effects of introduced laser reduced graphene oxide (rGO) layers at two positions in the tandem cell: 1) at the position between the top PK and bottom CIGS cell and 2) underneath the front transparent electrode. The purpose of introducing rGO layers is to improve the optoelectrical properties of the device, based on the tunable electronic and optical characteristics of rGO layers. Optical simulation results show that the parasitic absorption in rGO layers may noticeably affect the optical performance of the tandem cell if the layers are not optimized. The use of a thin and a few nanometer-thick rGO is suggested from the analysis if its parasitic absorption is not reduced. Directions for further optimization of optical rGO, including the reduction of parasitic absorption and tuning of the real part of the refractive index, are performed.

Highly flexible radial tandem junction thin film solar cells with excellent power-to-weight ratio

High power-to-weight ratio (PTWR) is an important figure-of-merit for high performance flexible/portable solar cells. Marrying advanced tandem junction design with three-dimensional (3D) Si nanowire (SiNW) framework enables a promising route to boost the PTWR. In this work, a radial tandem junction (RTJ) thin film solar cell has been demonstrated, for the first time, over SiNWs, which consist of radially deposited p-i-n multilayers with hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon germanium (a-SiGe:H) absorption layers in the outer and the inner junctions, respectively. The strong light trapping within the 3D SiNW framework allows for the use of a very thin a-SiGe:H (~45 nm) absorption layer to harvest efficiently the long wavelengths. The RTJ cells fabricated via a one-pump-down process in a single PECVD chamber, directly upon 15 µm thick aluminum foils demonstrate an excellent flexibility that can bend to 10 mm radius and achieve a record PTWR~1628 W/kg, and accomplish a high open-circuit voltage, filling factor and conversion efficiency of 1.2 V, 61.5% and 8.1% on glass, respectively, substantially improved compared to those accomplished by radial single junction cells. These results highlight the unique potential of 3D radial tandem technology to enable a new generation of high performance and durable flexible photovoltaics.

Improving the light absorption efficiency in thin-film plasmonic tandem solar cell

Recently, thin-film solar cells have received much attention due to low production cost. However, such cells suffer from low efficiency due to which they cannot be used for practical applications. To cater this problem, we have numerically investigated thin-film tandem solar cells comprising of double active layers made of amorphous silicon (a-Si) and crystalline silicon (c-Si) of different energy bandgaps. The tandem cell is found to absorb large amount of solar photons compared to a single a-Si and c-Si solar cells. To further improve the absorption efficiency, we efficiently utilized the surface plasmon resonance (SPR) effect of plasmonic nanoparticles, which are deposited in the form of a square lattice in the top a-Si active layer. The absorption characteristics of the cell are enhanced and tuned by optimizing the material and size of the nanoparticles. Moreover, periodic disorders are incorporated, which allow mixing of plasmonic modes having different angular momenta, resulting in a super broadband light absorption from 300 to 1100 nm and yielding a short circuit current density of 33.917 mA/cm2 in the active layers. The proposed plasmonic tandem cell can be advantageous for most of the photovoltaic applications.

Analysis of CIGS-based thin film tandem solar cell with ZnS buffer layers

In this paper, a thin film tandem solar cell based on CGS/CIGS structure incorporating ZnS buffer layers has been designed and its performance characteristics were obtained using Silvaco-Atlas 2D numerical simulator. A tandem cell with CdS buffer layers was also modeled and simulated with the same method for reference. Our results show that the tandem solar cell with ZnS buffer layers has a maximum conversion efficiency of 28.34% compared to a maximum conversion efficiency of 26.85% obtained for CdS-based tandem solar cell used as a reference. The maximum conversion efficiency for theoretically studied CdS-based tandem solar cell found in literature is 26.21%. Thus, ZnS can be used as a potential replacement for CdS that is notoriously known as a highly toxic compound. Optimum values of doping concentration and thickness are obtained for all layers of the solar cell. In addition, the effect of temperature on ZnS-based CGS/CIGS tandem cell was studied.

Performance improvement of Perovskite/CZTS tandem solar cell using low-cost ZnS/Ag/ITO multilayer spectrum splitter

In this paper, a new approach based on strategic combination between Dielectric1/Metal/Dielectric2 multilayer aspect and Particle Swarm Optimization (PSO) technique is proposed to design an efficient low-cost spectrum splitter for tandem solar cell applications. This approach allows selecting the suitable dielectric materials, noble metal and geometry of each sub-layer, providing high transparency, while maintaining a superior reflectance within well selected spectral ranges. It is revealed that the optimized ZnS/Ag/ITO multilayered structure offers 92% of transparency and a high reflectance of 89% with an optimum cut-off wavelength of 700 nm. These outstanding results are mainly attributed to the role of the adopted PSO approach in promoting an enhanced light-management. Subsequently, the influence of the optimized spectrum splitter on the solar cell efficiency is analyzed by implementing it in a Perovskite/CZTS tandem cell. It is found that the investigated cell exhibits a high efficiency exceeding 16%, far surpassing that of the conventional monolithic tandem photovoltaic device. This is due to the reduced optical and recombination losses enabled by the use of an optimized and low-cost spectrum splitter system. Therefore, the proposed strategy based on combined Dielectric1/Metal/Dielectric2 spectrum splitting and PSO metaheuristic technique pinpoints a new pathway towards reaching improved efficiencies, making it potential alternative for designing high-efficiency and cost-effective thin-film tandem solar cells.

Tunnel recombination junction influence on the a-Si:H/SHJ tandem solar cell

An effective tunnelling recombination junction (TRJ) is the most important part in a series connected tandem solar cell, and it always plays a significant role to match the current densities of individual solar cells. The aim of this paper is to find a TRJ that shows more efficient ohmic behavior compared to that used in typical thin film tandem solar cells, due to high current nature. Silicon heterojunction (SHJ) based tandem solar cell structure (a-Si:H/SHJ) was studied in detail with simulations using Advanced Semiconductor Analysis (ASA) software. Trap assisted recombination tunnelling and field enhanced mobility mechanisms have been included in our model analysis. Moreover, we also have simulated individual device characteristics of each a-Si:H (n-i-p), SHJ cell (top and bottom subcells of an a-Si:H/SHJ tandem cell), and correlated with the performance of the a-Si:H/SHJ tandem solar cell. The tandem device with a TRJ, the type which used in a thin film silicon tandem cell, shows low open circuit voltage (Voc) = 1.12 V and poor fill factor (FF) = 0.29 with S-shape in light current density–voltage (J-V) characteristics due to charge transport issue at the interface of top and bottom cells. An appropriate TRJ gives efficient recombination and an excellent ohmic contact at the interface between the subcells to match the current of each device. With the implementation of the optimum TRJ at the junction of two cells, Voc and FF have improved significantly to 1.35 V and 0.79 respectively. Also, we observed that the Voc of the tandem solar cell is nearly equal to the sum of the corresponding individual subcells, confirming no trapping related field loss at the junction.

Simulation, design and optimization of Si/InP thin-film tandem solar cell by using a plasmonic back reflector structure

In this paper, Si/InP thin-film tandem plasmonic solar cell was designed, simulated and optimized to obtain ultimate efficiency. The proposed solar cell structure has a periodic array of plasmonic back reflector which consists of a silver layer and two perpendicular silver nanowires placed on top of each other. This design creates a waveguide-scale structure by using a plasmonic back reflector with an anti-reflection coating layer on top, which dramatically enhances light trapping in the solar cell structure. In order to optimize the proposed solar cell structure, seven characteristic parameters of solar cell structure were optimized using the central composite design method. The optimized structures showed a maximum weighted absorption, ultimate efficiency and short-circuit current density of 0.982, 52% and 41.62 mA/cm2, respectively.

Thin-Film Tandem Organic Solar Cells With Improved Efficiency

Seeking high power conversion efficiency is always a striving pathway for many researchers to commercialize organic solar cells (OSCs). Thus, it is essential to achieve high conversion efficiency to make solar oriented devices as truly green energy resource. In this paper, we report novel tandem structures based on organic materials in which homo and hybrid schemes are utilized. The homo tandem structures involve the well-known organic materials such as P3HT: PCBM and PTB7: PCBM as top and bottom absorber layers, while the hybrid tandem structure is made by the combination of P3HT: PCBM and PTB7: PCBM, respectively. Due to different absorption coefficients, simulation results indicate that the hybrid tandem structure exhibit large values for current density J sc = 22.60mA/cm 2 , open circuit voltage V oc = 0.85V, fill factor FF = 68.21%, and efficiency η = 13.96%, compared to homo tandem cell and proves to be more efficient and highly stable towards high temperatures, which indicates that the proposed structure is more suitable for practical applications.

Enhancing PbS Colloidal Quantum Dot Tandem Solar Cell Performance by Graded Band Alignment.

Colloidal quantum dot solids are attractive candidates for tandem solar cells because of their widely tunable bandgaps. However, the development of the quantum dot tandem solar cell has lagged far behind that of its single-junction counterpart. One of the fundamental problems with colloidal quantum dot solar cells is the relatively small diffusion length, which limits the quantum dot absorbing layer thickness and hence the power conversion efficiency. In this research, guided by optical modeling and utilizing a graded band alignment strategy, a two-terminal monolithic solution-processed quantum dot tandem solar cell has been successfully fabricated and a power conversion efficiency of 6.8% has been achieved. The band grading approach utilized the complementary tuning of work functions and band alignment through judicious choices of the nanoparticle surface chemistry and quantum dot confined size. This work demonstrates a general approach to improving the efficiency for tandem thin-film solar cells.

Bimolecular Additives Improve Wide-Band-Gap Perovskites for Efficient Tandem Solar Cells with CIGS

Summary Tandem solar cells coupling narrow- and wide-band-gap thin-film polycrystalline absorbers are attractive for achieving ultrahigh efficiency with low manufacturing cost. For established narrow-band-gap CIGS thin-film bottom cells, a challenge is to develop highly efficient polycrystalline wide-band-gap top cells. Here, we demonstrate a 1.68-eV (FA0.65MA0.20Cs0.15)Pb(I0.8Br0.2)3 wide-band-gap perovskite solar cell with an efficiency of ∼20% enabled by using PEAI and Pb(SCN)2 complementary additives in the perovskite precursor. The coupling of PEA+ and SCN− provides a synergistic effect that overcomes growth challenges with either additive individually and improves perovskite film quality with enhanced crystallinity, reduced formation of excess PbI2 (in comparison to using Pb(SCN)2 additive alone), lower defect density and energetic disorder, and an improved carrier mobility (∼47 cm2 V−1s−1) and lifetime (∼2.9 μs). When coupling a semi-transparent 1.68-eV perovskite top cell fabricated by this approach with a 1.12-eV CIGS bottom cell, we achieve 25.9%-efficient polycrystalline perovskite/CIGS 4-terminal thin-film tandem solar cells.

Fabrication of p-type BaCuSF and n-type In2O3:Sn bilayer films and their applications to the back contact of CdS/CdTe solar cells

For applications to polycrystalline thin-film tandem solar cells, we studied p-type conductive BaCuSF single layer and p-type BaCuSF and n-type In2O3:Sn (ITO) bilayer films. The BaCuSF films were prepared by pulsed laser deposition (PLD), and the ITO films were prepared by RF sputtering. The bilayer film showed ohmic current–voltage characteristic. A tunnel junction between these two layers was successfully fabricated, because p-type BaCuSF and n-type ITO layers had sufficiently high carrier concentrations. The BaCuSF/ITO bilayer films were employed as the back electrodes of CdS/CdTe solar cells. A CdTe solar cell with a 20-nm-thick BaCuSF/a 300-nm-thick ITO bilayer back contact showed a high conversion efficiency of 13.9% (VOC = 818 mV, JSC = 25.2 mA/cm2, and FF = 0.675), which was higher than that of a CdTe solar cell with a BaCuSF single-layer back contact (11.1%). The efficiency is comparable to that of a CdTe solar cell with a SrCuSeF/ITO bilayer back contact (14.3%).

Optical design of perovskite solar cells for applications in monolithic tandem configuration with CuInSe2 bottom cells

Abstract:Monolithic integrated thin film tandem solar cells consisting of a high bandgap perovskite top cell and a low bandgap thin film bottom cell are expected to reach higher power conversion efficiencies (PCEs) with lower manufacturing cost and environmental impacts than the market-dominant crystalline silicon photovoltaics. There have been several demonstrations of 4-terminal and 2-terminal perovskite tandem devices with CuInGaSe2 (CIGS) or CuInSe2 (CIS) and, similar to the other tandem structures, the optimization of this device relies on optimal choice for the perovskite bandgap and thickness. Therefore, further advancement will be enabled by tuning the perovskite absorber to maximize the photocurrent limited by the current match condition. Here, we systematically study the optical absorption and transmission of perovskite thin films with varying absorber band gap. Based on these results, we model the photocurrent generations in both perovskite and CIS subcells and estimate the performances of projected tandem devices by considering the ideally functioning perovskite and CIS device. Our results show that for perovskite layers with 500 nm thickness the optimal bandgap is around 1.6 eV. With these configurations, PCEs above 20% could be achieved by monolithically integrated perovskite/CIS tandem solar cells. Also by modelling the absorption at every layer we calculate the quantum efficiency at each subcell in addition to tracking optical losses.

Variation in efficiency with change in band gap and thickness in thin film amorphous silicon tandem heterojunction solar cells with AFORS-HET.

Numerical simulation of both single and double absorbing layers in amorphous silicon thin film solar cell is performed with the use of AFORS-HET. A single absorbing layer solar cell with both a-SiH and a-SiGeH is designed and compared with a tandem heterojunction solar cell, a-SiC/a-SiH/a-Si(i)/a-SiGeH. Design parameters are investigated, compared and optimized. The maximum efficiency for each single absorbing layer and for a tandem heterojunction thin film solar cell, a-SiC/a-SiH/a-Si(i)/a-SiGeH, is predicted. The results are validated by comparing with two different method of analysis.

Optimization approach for optical absorption in three-dimensional structures including solar cells

The rigorous coupled-wave approach (RCWA) and the differential evolution algorithm (DEA) were coupled in a practicable approach to maximize absorption in optical structures with three-dimensional morphology. As a model problem, optimal values of four geometric parameters and the bandgaps of three i-layers were found for an amorphous-silicon, multi-terminal, thin-film tandem solar cell comprising three p-i-n junctions with a metallic hexagonally corrugated back-reflector. When the optical short-circuit current density was chosen as the figure of merit to be maximized, only the bandgap of the topmost i-layer was significant and the remaining six parameters played minor roles. While this configuration would absorb light very well, it would have poor electrical performance. This is because the optimization problem allows for the thicknesses and bandgaps of the semiconductor layers to change. We therefore devised another figure of merit that takes into account bandgap changes by estimating the open-circuit voltage. The resulting configuration was found to be optimal with respect to all seven variable parameters. The RCWA+DEA optimization approach is applicable to other types of photovoltaic solar cells as well as optical absorbers, with the choice of the figure of merit being vital to a successful outcome.

Economic viability of thin-film tandem solar modules in the United States

Tandem solar cells are more efficient but more expensive per unit area than established single-junction (SJ) solar cells. To understand when specific tandem architectures should be utilized, we evaluate the cost-effectiveness of different II–VI-based thin-film tandem solar cells and compare them to the SJ subcells. Levelized cost of electricity (LCOE) and energy yield are calculated for four technologies: industrial cadmium telluride and copper indium gallium selenide, and their hypothetical two-terminal (series-connected subcells) and four-terminal (electrically independent subcells) tandems, assuming record SJ quality subcells. Different climatic conditions and scales (residential and utility scale) are considered. We show that, for US residential systems with current balance-of-system costs, the four-terminal tandem has the lowest LCOE because of its superior energy yield, even though it has the highest US$ per watt (US$ W–1) module cost. For utility-scale systems, the lowest LCOE architecture is the cadmium telluride single junction, the lowest US$ W–1 module. The two-terminal tandem requires decreased subcell absorber costs to reach competitiveness over the four-terminal one. Multijunction solar cells are more efficient and more expensive than single-junction photovoltaic cells, but their cost-effectiveness remains unclear. Here, Sofia et al. study the manufacturing costs of thin-film devices to analyse the levelized cost of electricity of single and multijunctions in the United States.