Tandem Solar Cell Configurations Research Articles

Advances in Top Transparent Electrodes by Physical Vapor Deposition for Buffer Layer‐Free Semitransparent Perovskite Solar Cells

The advancements in halide perovskite materials, celebrated for their exceptional optoelectronic properties, have not only led to a remarkable increase in the efficiency of perovskite solar cells (PSCs) but also opened avenues for the development of semitransparent devices. Such devices are ideally suited for integration into building facades and for use in tandem solar cell configurations. However, depositing transparent electrodes (TEs) on top of the charge transport layers in PSC poses significant challenges. Physical vapor deposition (PVD), commonly used in the industry to prepare transparent conducting oxides (TCOs) as TEs, can introduce plasma‐induced damage during the process, which decreases the efficiency of the final devices. While incorporating a buffer layer is the typical approach to mitigate plasma damage, it also increases the complexity and costs of solar cell fabrication. This perspective focuses on the developments of buffer‐free semitransparent PSCs. It highlights the shift away from the typical approach of incorporating a buffer layer. Through a comprehensive analysis of recent research, this work presents successful cases of direct TCO deposition onto transport layers, evaluates scalability and stability, and concludes with recommendations for optimizing PVD processes in the fabrication of buffer‐free PSCs.

Surface heterojunction based on n-type low-dimensional perovskite film for highly efficient perovskite tandem solar cells.

Enhancing the quality of junctions is crucial for optimizing carrier extraction and suppressing recombination in semiconductor devices. In recent years, metal halide perovskite has emerged as the most promising next-generation material for optoelectronic devices. However, the construction of high-quality perovskite junctions, as well as characterization and understanding of their carrier polarity and density, remains a challenge. In this study, using combined electrical and spectroscopic characterization techniques, we investigate the doping characteristics of perovskite films by remote molecules, which is corroborated by our theoretical simulations indicating Schottky defects consisting of double ions as effective charge dopants. Through a post-treatment process involving a combination of biammonium and monoammonium molecules, we create a surface layer of n-type low-dimensional perovskite. This surface layer forms a heterojunction with the underlying 3D perovskite film, resulting in a favorable doping profile that enhances carrier extraction. The fabricated device exhibits an outstanding open-circuit voltage (VOC) up to 1.34V and achieves a certified efficiency of 19.31% for single-junction wide-bandgap (1.77eV) perovskite solar cells, together with significantly enhanced operational stability, thanks to the improved separation of carriers. Furthermore, we demonstrate the potential of this wide-bandgap device by achieving a certified efficiency of 27.04% and a VOC of 2.12V in a perovskite/perovskite tandem solar cell configuration.

New numerical model for a 2T-tandem solar cell device with narrow band gap SWCNTs reaching efficiency around 35 %

With a large-band gap top cell and a low-band gap bottom cell, double-junction tandem solar cells have a huge potential to exceed existing single-junction photovoltaic technology. To fully benefit, serious attention must go into the choice and performance amelioration of both cells. Tandem solar cells with two terminals (2 T) are highly efficient in converting energy. As the 2 T tandem solar cell configuration is equivalent to an electric series connection between the sub-cells, one of its key constraints is the circulation of current density. The monolithic device's performance is constrained because the sub-cell with the lowest current (top cell) forces it to run at its value. Using a bottom sub-cell made of Single-Walled Carbon Nanotubes (SWCNTs), which has an interesting current density and matches the top cell, is a possible solution for such a challenge as presented in this simulation work. The 2 T monolithic solar cell resulting from this study offers interesting photovoltaic parameters with an excellent fill factor and power conversion efficiency of 34.8 %.

Insights into the charge carrier dynamics in perovskite/Si tandem solar cells using transient photocurrent spectroscopy

Direct bandgap perovskite and indirect bandgap Si, which form the two active layers in a tandem solar cell configuration, have different optoelectronic properties and thicknesses. The charge-carrier dynamics of the two-terminal perovskite-on-Si tandem solar cell in response to a supercontinuum light pulse is studied using transient photocurrent (TPC) measurements. Spectral dependence of TPC lifetime is observed and can be classified into two distinct timescales based on their respective carrier generation regions. The faster timescale (∼500 ns) corresponding to the spectral window (300–750 nm) represents the top-perovskite sub-cell, while the slower timescale regime of ∼25 μs corresponds to the bottom-Si sub-cell (>700 nm). Additionally, under light-bias conditions, the transient carrier dynamics of the perovskite sub-cell is observed to be coupled with that of the Si sub-cell. A sharp crossover from the fast-response to a slow-response of the device as a function of the light-bias intensity is observed. These results along with a model based on transfer matrix formulation highlight the role of charge-carrier dynamics in accessing higher efficiencies in tandem solar cells. The carrier transit times and lifetimes in addition to their optical properties need to be taken into account for optimizing the performance.

Over 30% efficiency bifacial 4-terminal perovskite-heterojunction silicon tandem solar cells with spectral albedo

We developed and designed a bifacial four-terminal perovskite (PVK)/crystalline silicon (c-Si) heterojunction (HJ) tandem solar cell configuration albedo reflection in which the c-Si HJ bottom sub-cell absorbs the solar spectrum from both the front and rear sides (reflected light from the background such as green grass, white sand, red brick, roofing shingle, snow, etc.). Using the albedo reflection and the subsequent short-circuit current density, the conversion efficiency of the PVK-filtered c-Si HJ bottom sub-cell was improved regardless of the PVK top sub-cell properties. This approach achieved a conversion efficiency exceeding 30%, which is higher than those of both the top and bottom sub-cells. Notably, this efficiency is also greater than the Schockley–Quiesser limit of the c-Si solar cell (approximately 29.43%). The proposed approach has the potential to lower industrial solar cell production costs in the near future.

Potential high efficiency of GaAs solar cell with heterojunction carrier selective contact layers

Advanced configurations of gallium arsenide (GaAs) solar cells are proposed, using hydrogenated amorphous silicon (a-Si: H) and zinc oxide (ZnO) layers as passivation and carrier selective contacts (CSC), as alternatives to the conventional epitaxial GaInP CSC layers. The cell operation is simulated based on the AFORS-HET simulation program. The results show that with a wide-gap ZnO window layer, single-junction GaAs solar cells can reach a higher short-circuit current density (Jsc) and open-circuit voltage (Voc) than that obtained with conventional GaInP CSC layers without affecting the fill factor (FF). Notably, wide-gap and n-type doping ZnO layers show great potential as electron selective contacts in GaAs solar cells with high barriers at the valence band for blocking hole-transport. An efficiency of 30% is reached for a single-junction GaAs cell with a front ZnO electron selective contact. A 4-terminal GaAs/c-Si tandem solar cell configuration with an estimated conversion performance of 35.16% is proposed. These results indicate enormous potential for the development of low-cost and high-efficiency GaAs-based solar cells in the future.

Band gap and thickness optimization for improvement of CIGS/CIGS tandem solar cells using Silvaco software

In this study, we investigated numerical simulations of the double junction solar cells based copper indium gallium diselenide (CIGS/CIGS) using the two-dimensional device simulator Silvaco-Atlas under standard AM1.5G Illumination. We considered the CIGS absorbing layer thickness and its bandgap of sub-cells as key parameters to optimize the performance of the CIGS/CIGS tandem solar cell. The electrical parameters of the best CIGS/CIGS tandem solar cell configuration were a short circuit current density (Jsc) of 18.82mA/cm², an open-circuit voltage (Voc) of 1.84V, a fill factor (FF) of 82.54 %, and the conversion efficiency (η) of 27.03 %. The optimal CIGS absorbing layer thickness of the top and bottom cells corresponding to maximum conversion efficiency obtained were 0.18μm and 3.2μm, respectively, while the optimal band gaps were 1.68eV for top cell and 1.13eV for the bottom cell. These results can be used as a basis for effectively developing low-cost and high-efficiency solar cells.

TCAD 2D numerical simulations for increasing efficiency of AlGaAs – GaAs Solar Cells

The performance of solar cells has improved quickly in recent years, the latest research focuses on thin cells, multijunction cells, solar cells of the group III-V compounds, Tandem cells, etc. In the present work, numerical simulations are developed, using SENTAURUS TCAD as a tool, in order to obtain a solar cell model based on Galium Arsenide (GaAs). This solar cell corresponds to the so-called "Thin Films" due to the fact that can make layers thinner than we would have if we work with conventional semiconductors, such as; Silicon or Germanium; thus opening the possibility of placing the cell as a top layer within a tandem solar cell configuration with compounds of group III-V. That is why two types of simulations are performed with respect to the contact of the rear contact; one corresponds to the cell with a lower contact equal to the length of the cell and the other with a small contact of 5 μm. In addition, the cell undergoes an optimization process by modifying the geometry and doping of the layers that comprise it, in order to improve its performance. To achieve this objective, the initial conditions and the appropriate simulation parameters must be determined, which have been selected and corroborated with the literature, allowing us to arrive at coherent results and optimal models of solar cell design through numerical simulations.

Simulations of Non-Monolithic Tandem Solar Cell Configurations for Electrolytic Fuel Generation

The efficient conversion of solar energy to fuels through electrochemical processes requires optimizing the photovoltage and current for an ideal coupling with the electrolysis reaction. A modular architecture for tandem photovoltaics is explored and modeled as a strategy to drive an arbitrary electrolysis reaction from sunlight to produce the maximum fuel product in a day. Non-monolithic tandem solar cells based on Si and organometal halide perovskites are simulated in two-terminal and four-terminal arrangements and coupled with experimental data on water-splitting and CO2 reduction to predict the performance of an integrated solar fuels system. An appropriately designed four-terminal system is modeled to match or exceed the output of a two-terminal system. The four-terminal configuration leads to a 15.8% increase in daily H2 production with a 1.5 eV/1.12 eV system, and a 5.3% increase with a more ideal 1.74 eV/1.12 eV combination. The four-terminal system is also simulated to match the production of formic acid and increase the production of ethylene by 20.4% in a Cu-catalyzed CO2 reduction process compared to a two-terminal tandem arrangement. The effects of series resistance in non-monolithic tandem devices are modeled as well, showing a much greater tolerance to cell width in the four-terminal systems.

Performance of silicon solar cells under filtered spectra and different light intensities

Solar cells operate under various light intensities. In addition, in a tandem solar cell configuration, the bottom cell receives a spectrum that is filtered by the top cell. The performance of the bottom cell at low light intensity is thus of great importance. In this paper, we study various types of silicon solar cells under various light intensities and filtered spectra. We find that, as expected, the short-circuit current varies linearly with the illumination intensity, regardless of the input spectrum. However, we also observe that for a constant number of incident photons but different long-pass filters (i.e., different photogeneration profiles), the short-circuit current density of the solar cells reduces with increasing cut-on wavelength of the used filter. According to our analysis, the loss in short-circuit current can be partly explained by the strong wavelength dependence of the external quantum efficiency at long wavelengths (1050–1200 nm) as well as the different carrier generation profiles under filtered spectra.

Progress in Tandem Solar Cells Based on Hybrid Organic–Inorganic Perovskites

Owing to their high efficiency, low‐cost solution‐processability, and tunable bandgap, perovskite solar cells (PSCs) made of hybrid organic‐inorganic perovskite (HOIP) thin films are promising top‐cell candidates for integration with bottom‐cells based on Si or other low‐bandgap solar‐cell materials to boost the power conversion efficiency (PCE) beyond the Shockley‐Quiesser (S‐Q) limit. In this review, recent progress in such tandem solar cells based on the emerging PSCs is summarized and reviewed critically. Notable achievements for different tandem solar cell configurations including mechanically‐stacked, optical coupling, and monolithically‐integrated with PSCs as top‐cells are described in detail. Highly‐efficient semitransparent PSC top‐cells with high transmittance in near‐infrared (NIR) region are critical for tandem solar cells. Different types of transparent electrodes with high transmittance and low sheet‐resistance for PSCs are reviewed, which presents a grand challenge for PSCs. The strategies to obtain wide‐bandgap PSCs with good photo‐stability are discussed. The PCE reduction due to reflection loss, parasitic absorption, electrical loss, and current mismatch are analyzed to provide better understanding of the performance of PSC‐based tandem solar cells.

Simulations of non-monolithic tandem solar cell configurations for electrolytic fuel generation

Multi-terminal tandem solar cell configurations were modeled for driving water-splitting and CO2 reduction to maximize fuel production throughout the day.

High efficiency, magnetron sputtered CdS/CdTe solar cells

Polycrystalline II–VI semiconductor materials show great promise for efficient, low-cost photovoltaics. Large-area deposition of the II–VI semiconductors such as CdTe is possible by a variety of methods but the use of a plasma-based method such as magnetron sputtering can have significant advantages. Here we present recent results in the fabrication of CdS/CdTe cells using rf magnetron sputtering and discuss some of the advantages that accrue from the use of sputtering methods in this class of materials. Some of these advantages are particularly relevant as the polycrystalline thin-film PV community addresses issues related to the fabrication of tandem cells with efficiencies over 25%. Our best results have been obtained with sputtered ZnO:Al to achieve a CdTe solar cell having 14.0% efficiency at one sun with an air mass 1.5 global spectrum. We have also studied reactive sputtering of ZnTe:N which shows promise for use as a transparent back contact or as a recombination junction with ZnO:Al for II–VI based alloy top cells in a tandem solar-cell configuration. Finally, some advances have been made in substrate-configuration CdTe cells on Mo using sputter deposition that hold promise for flexible CdTe-based PV.

N-CdS/p-ZnIn 2Se 4 thin film solar cell

The photovoltaic behaviour of a CdS/ZnIn 2Se 4 vacuum-evaporated thin film solar cell is reported for the first time. Because of the band gap of ZnIn 2Se 4 (1.93 eV) this combination of semiconductor materials seems to be suitable for use as one of the junctions in tandem solar cell configurations. Uncoated cells exhibited efficiencies of the order of 1.5% under an illumination of 100 mW cm -2.