All-perovskite Tandem Solar Cells Research Articles

Unveiling the ambipolar carrier transport property of SnO2−X for multiple-functional interlayers in perovskite solar cells

Tin oxides are the most promising electron transport layers in perovskite solar cells. An ambipolar carrier transport property has been recently demonstrated which enables a simple interconnection structure for all-perovskite tandem solar cells. However, the underlying mechanism for its ambipolar behavior is unclear, which cannot be explained by the intrinsic defects in SnO2−x. Here, by using density functional theory calculations, we unveil the origin of the ambipolar carrier transport of non-stoichiometry SnO2−x with a structure of SnO embedded in the SnO2 matrix. The hybridization of O 2p and Sn 5s orbitals of SnO introduces mid-gap states in the bandgap of SnO2, enabling hole transport property for SnO2−x when x is > 0.2. Increasing the percentage of SnO in SnO2−x significantly enhances the hole transport capability of SnO2−x due to the enlarged Sn–O–Sn angles that increase orbital overlapping between O and Sn atoms, thus providing strategies for the further tuning of the carrier transport properties of SnO2−x by compositional and structural designs.

Optical design of TCO-free interconnecting layer for all-perovskite tandem solar cells

Organic–inorganic hybrid perovskite materials are excellent candidates as light absorbers in tandem solar cells with advantages of tunable bandgaps, high absorption coefficients, and facile and low-cost fabrication processes. As the key component of a tandem structure, the interconnecting layer (ICL) requires optical transparency, efficient carrier recombination, and facile up-scalability. To demonstrate the feasibility of an efficient TCO-free ICL in all-perovskite tandem solar cell devices, we have performed a comprehensive computational analysis using the transfer matrix method. The results suggest that varying the silver recombination layers up to 3 nm does not present a significant effect on the maximum achievable photocurrent (MAPC) of the cell. Moreover, the highest MAPC from the tandem cell with the lowest sensitivity to electron and hole transport layer thicknesses can be obtained by the transport layers with refractive indices within the range of 1.9–2.6. The findings are of direct practical relevance, i.e., with meeting our optical framework, a fabrication procedure can be merely directed toward the electrical optimization of the ICL. The presented methodology can serve as an introduction to benchmark ICL design for multi-junction excitonic solar cells.

A new all-inorganic vacancy-ordered double perovskite Cs2CrI6 for high-performance photovoltaic cells and alpha-particle detection in space environment

Although MAPbI3 photovoltaics have gained increasing interest for space application, its low stability and radiation resistance is insurmountable. Here, we unexpectedly find a new vacancy-ordered double perovskite Cs2CrI6 to realize high-performance space solar cells and α-particle detectors through an innovative multi-scale simulation strategy based on the first-principle calculations coupling with drift-diffusion model and Monte Carlo method. Compared to the MAPbI3, Cs2CrI6 possesses more excellent stability and optical absorption, suitable band gap (1.08 eV), higher mobility (∼103 cm2/V) and lower capture cross-section. These lead to the ultra-high power conversion efficiency (PCE) for single-junction solar cells (22.4%) and monolithic all-perovskite tandem solar cells (26.6%), and excellent α-particle detectors with ultra-high charge collection efficiency (CCE = 99.3%) and mobility-lifetime product (μτh = 4.99 × 10−3 cm2V−1), which are superior to those of corresponding MAPbI3 devices. Meanwhile, the 90% of initial PCE can be remained even under the 5 × 1013 p. cm−2 fluence proton beam and several orders higher than traditional space solar cell. Moreover, the proton irradiation resistance of Cs2CrI6 α-particle detection can reach up to 1016 p. cm−2. The excellent device performance and irradiation resistance of Cs2CrI6 devices indicate the great potential application in photovoltaic cells, α-particle detectors and even their space applications.

Monolithic all-perovskite tandem solar cells: recent progress and challenges

All-perovskite tandem solar cells (TSCs) show great potential for achieving efficiencies beyond the Shockley–Queisser limit owing to their excellent photovoltaic properties and cost effectiveness. In this review, the current status of all-perovskite TSCs as well as recent research progress are introduced with a focus on three main strategies: optimization of the interconnecting layer (ICL), suppression of tin oxidation in low-bandgap perovskites, and prevention of halide segregation in wide-bandgap perovskites. The development of triple-junction all-perovskite devices and remaining issues facing all-perovskite TSCs are also discussed.

Optoelectronic modeling and sensitivity analysis of a four-terminal all-perovskite tandem solar cell – Identifying pathways to improve efficiency

We develop an optoelectronic model for a four-terminal all-perovskite tandem solar cell comprising a top and a bottom cell that are mechanically stacked together. In essence, the model captures conservation of charge carriers, the electric field via the Poisson equation, the coherent and incoherent light propagation and subsequent carrier generation and recombination mechanisms. Experiments for the stand-alone bottom and top cells as well as the tandem cell calibrate and validate the model with overall good agreement. To elucidate the relative importance of the geometrical and material parameters, a stochastic Monte Carlo simulation is carried out with a sample size of ten thousand for thirty-six simultaneously varied parameters. These parameters are ranked according to their influence on the efficiencies of the top, bottom, and tandem cell: The thicknesses for the top- and bottom-cell transparent electrode layers are ranked amongst the highest. Finally, we show how one can fine-tune the layer thicknesses to enhance the tandem efficiency from the base case of 23.1% to 24.4% and carry out further optimizations.

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Summary The development of mixed tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) with low band gap (1.2–1.4 eV) has become critical not only for pushing single-junction devices toward the maximum efficiency given by the Shockley-Queisser limit, but also for enabling all-perovskite tandem devices beyond this limit. However, achieving high power-conversion efficiency (PCE) and long-term device operation stability simultaneously remains a significant challenge for Sn-Pb-based PSCs. Here, we demonstrate near ideal-band-gap (∼1.34 eV) methylammonium-free Sn-Pb-based PSCs with high efficiency (∼20%) and promising operational stability of maintaining >80% of initial PCE over 750 h under maximum-power-point tracking. The key to this success is the use of a SnCl2⋅3FACl complex additive that improves the microstructure and reduces the development of residual stress in the Sn-Pb perovskite thin films, which in turn enhances the efficiency and stability of the Sn-Pb-based ideal-band-gap PSCs.

Optical and Electronic Losses Arising from Physically Mixed Interfacial Layers in Perovskite Solar Cells.

Perovskite solar cell device performance is affected by optical and electronic losses. To minimize these losses in solar cells, it is important to identify their sources. Here, we report the optical and electronic losses arising from physically mixed interfacial layers between the adjacent component materials in highly efficient two terminal (2T) all-perovskite tandem, single-junction wide-bandgap, and single-junction narrow-bandgap perovskite-based solar cells. Physically mixed interfacial layers as the sources of optical and electronic losses are identified from spectroscopic ellipsometry measurements and data analysis followed by comparisons of simulated and measured external quantum efficiency spectra. Parasitic absorbance in the physically mixed regions between silver metal electrical contacts and electron transport layers (ETLs) near the back contact and a physical mixture of commercial indium tin oxide and hole transport layers (HTL) near the front electrical contact lead to substantial optical loss. A lower-density void + perovskite nucleation layer formed during perovskite deposition at the interface between the perovskite absorber layer and the HTL causes electronic losses because of incomplete collection of photogenerated carriers likely originating from poor coverage and passivation of the initially nucleating grains.

Limiting factors and improving solutions of P-I-N type tin-lead perovskite solar cells performance

In order to break through the limit of Shockley-Queisser (SQ) radiation and further improve the efficiency of perovskite solar cells, tin-lead perovskite solar cells have widely and successfully been used as narrow-bandgap bottom cells in all-perovskite tandem solar cells. The highest efficiency of tin-lead perovskite solar cells has recently reached 21.7%, which, however, is still lower than that of lead-based perovskite solar cells. This article analyzes the main factors that limit the further improving of their performances, and summarizes the effective solutions proposed by researchers in recent years. The main points are as follows: 1) by adding tin-rich additives, strong reducing agents or compounds containing large organic cations, Sn<sup>2+</sup> oxidation is inhibited and the p-doped degree of tin-lead perovskite and the open-circuit voltage loss are reduced; 2) through regulating the composition, changing the method of preparing the perovskite film, adding functional groups or solvent engineering, the crystallization rate of tin-lead perovskite film is delayed and the crystallization quality of the film is improved; 3) by selecting an appropriate electron transport layer or hole transport layer the influence of energy level mismatch on carrier transport or the instability of carrier transport layer on devices can be avoided. Finally, the future development of Sn-Pb perovskite solar cells is prospected. It is believed that the tin-lead perovskite solar cells can realize not only the high efficiency and stable single-junction solar cells, but also high efficiency perovskite-perovskite tandem solar cells.

Wide-bandgap organic–inorganic hybrid and all-inorganic perovskite solar cells and their application in all-perovskite tandem solar cells

We summarize the progress in organic–inorganic hybrid and all-inorganic wide-Egperovskite solar cells. Key challenges and effective strategies are discussed, followed by applications in tandems. We outline perspectives to design superior devices.

Progress of all-perovskite tandem solar cells: the role of narrow-bandgap absorbers

Perovskite solar cells (PSCs) have gained increasing attention due to their excellent photovoltaic performance, achieving certified power conversion efficiency (PCE) of 25.2%. To further enhance PCE and break the Shockley-Queisser limit of the single junction PSCs, great efforts have been made in tandem solar cells based on perovskite, including perovskite/Si, and perovskite/perovskite (all-perovskite). Among them, all-perovskite tandem solar cells exhibit unique advantages of both low-cost fabrication and high efficiency. They have advanced rapidly in these years, due to the realization of stable and efficient narrow-bandgap perovskites. In this work, we review the development of monolithic all-perovskite tandem solar cells and highlight the critical role of narrow-bandgap perovskites in recent progress of all-perovskite solar cells. We also propose our perspective of future directions on this subject.

Tin-Based Defects and Passivation Strategies in Tin-Related Perovskite Solar Cells

Tin (Sn)-based and mixed tin–lead (Sn–Pb) perovskites have attracted increased attention as promising candidates for new generation lead-free perovskite and all-perovskite tandem solar cells. Howev...

16.8% Monolithic all-perovskite triple-junction solar cells via a universal two-step solution process

Perovskite semiconductors hold a unique promise in developing multijunction solar cells with high-efficiency and low-cost. Besides design constraints to reduce optical and electrical losses, integrating several very different perovskite absorber layers in a multijunction cell imposes a great processing challenge. Here, we report a versatile two-step solution process for high-quality 1.73 eV wide-, 1.57 eV mid-, and 1.23 eV narrow-bandgap perovskite films. Based on the development of robust and low-resistivity interconnecting layers, we achieve power conversion efficiencies of above 19% for monolithic all-perovskite tandem solar cells with limited loss of potential energy and fill factor. In a combination of 1.73 eV, 1.57 eV, and 1.23 eV perovskite sub-cells, we further demonstrate a power conversion efficiency of 16.8% for monolithic all-perovskite triple-junction solar cells.

All-perovskite tandem solar cells with 24.2% certified efficiency and area over 1 cm2 using surface-anchoring zwitterionic antioxidant

Monolithic all-perovskite tandem solar cells offer an avenue to increase power conversion efficiency beyond the limits of single-junction cells. It is an important priority to unite efficiency, uniformity and stability, yet this has proven challenging because of high trap density and ready oxidation in narrow-bandgap mixed lead–tin perovskite subcells. Here we report simultaneous enhancements in the efficiency, uniformity and stability of narrow-bandgap subcells using strongly reductive surface-anchoring zwitterionic molecules. The zwitterionic antioxidant inhibits Sn2+ oxidation and passivates defects at the grain surfaces in mixed lead–tin perovskite films, enabling an efficiency of 21.7% (certified 20.7%) for single-junction solar cells. We further obtain a certified efficiency of 24.2% in 1-cm2-area all-perovskite tandem cells and in-lab power conversion efficiencies of 25.6% and 21.4% for 0.049 cm2 and 12 cm2 devices, respectively. The encapsulated tandem devices retain 88% of their initial performance following 500 hours of operation at a device temperature of 54–60 °C under one-sun illumination in ambient conditions. Ensuring both stability and efficiency in mixed lead–tin perovskite solar cells is crucial to the development of all-perovskite tandems. Xiao et al. use an antioxidant zwitterionic molecule to suppress tin oxidation thus enabling large-area tandem cells with 24.2% efficiency and operational stability over 500 hours.

Enhancing the Performance of Two-Terminal All-Perovskite Tandem Solar Cells by the Optical Coupling Layer Beyond the Antireflection Function

All-perovskite tandem solar cells have great potential to realize the efficiency beyond the Shockley-Queisser efficiency limitation of single junction solar cells. Here we investigate the photon redistribution effect induced by introduction of the optical coupling layer in two terminal (2 T) tandem solar cells. In this work, it is shown that the introduction of the optical coupling layer could not only reduce the reflection loss, but also would affect the redistribution of the absorbed photons in the tandem device due to the optical interference effect, which will disturb the previous balance and complicate the optical modulation. This photon redistribution phenomenon is systemically investigated by combining the optical and electrical aspects. By considering the coupling effect beyond the antireflection function after introducing the optical coupling layer, the new current match could be achieved, which would obviously improve the device performance further. Various materials such as LiF, MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , ZnO have been adopted as the optical coupling layer and it is demonstrated that this phenomenon is universal for all the cases. The improvement brought by photon redistribution effect may be even more obvious than antireflection function. Through analyzing the inner optical mechanism and modulating the structure, a higher performance can be achieved by carefully considering the optical coupling effect.

Low-bandgap mixed tin–lead iodide perovskites with reduced methylammonium for simultaneous enhancement of solar cell efficiency and stability

High-performance perovskite/perovskite tandem solar cells require high-efficiency and stable low-bandgap perovskite subcells. State-of-the-art low-bandgap mixed tin–lead iodide perovskite solar cells exhibit either a high power-conversion efficiency or improved stability, but not both. Here we report a two-step bilayer interdiffusion growth process to simultaneously meet both requirements for formamidinium-based low-bandgap mixed tin–lead iodide perovskite solar cells. The bilayer interdiffusion growth process allows for the formation of high-quality and large-grained perovskite films with only 10 mol% volatile methylammonium. Additionally, one-dimensional pyrrolidinium perovskite was applied to passivate the perovskite film and improve the junction quality, which resulted in a carrier lifetime of 1.1 μs and an open circuit voltage of 0.865 V for our perovskite film and device with a bandgap of 1.28 eV. Our strategies enabled a power-conversion efficiency of 20.4% for low-bandgap perovskite solar cells under AM 1.5G illumination. More importantly, an encapsulated device can retain 92% of its initial efficiency after 450 h of continuous 1 sun illumination. Low-bandgap tin–lead perovskites are key to all-perovskite tandem solar cells but simultaneous improvement in efficiency and stability has proven challenging. Now, Li et al. fabricate tin–lead perovskite cells with reduced methylammonium content that are 20.4% efficient and stable under illumination for 450 h.

All-Perovskite Tandem Solar Cells: A Roadmap to Uniting High Efficiency with High Stability

ConspectusOrganic–inorganic halide perovskite photovoltaics (PVs)─only a decade-old field─have reached impressive power conversion efficiencies (PCEs) and passed industrial stability requirements (IEC 61215:2016 Damp Heat and Humidity Freeze tests), solidifying their status among candidates for next generation PVs. Among the various perovskite PV technologies, all-perovskite tandem solar cells (PTSCs) are frontrunners for commercialization. PTSCs unite a narrow-bandgap (NBG; Eg ≈ 1.2 eV) perovskite back cell with a wide-bandgap (WBG; Eg ≈ 1.7–1.9 eV) perovskite front cell. Despite their nascency, PTSCs have achieved certified PCEs of 24.8% and 24.2% for small-area (0.049 cm2) and large-area devices (1.041 cm2), respectively. With further advances in materials development, PTSCs are capable of moving beyond the PCE limits of single-junction cells due to reduced thermalization losses and improved utilization of the solar spectrum. By contrast, the PCE of single-junction perovskite devices is already approaching its saturation level, which is already very close to the device’s Shockley–Queisser limit for a bandgap of around 1.55 eV. The tandem architecture, thus, provides the most viable path forward to further exploiting the potential of perovskite solar cells.However, PTSC technology faces a set of challenges distinct from those in perovskite single-junction devices because (i) NBG perovskites─typically achieved by Pb–Sn alloying─are prone to oxidation (Sn2+ to Sn4+), which results in a high density of Sn vacancies that degrade the optoelectronic performance of NBG perovskite films, (ii) practically complete photon absorption and charge extraction require thick, NBG perovskite films having long carrier diffusion lengths, and (iii) WBG perovskites with high Br/(I + Br) ratio experience large voltage losses and inferior light stability due to surface trap states and phase segregation.In this Account, we discuss how to manage these considerations and maximize the power output in PTSCs via light management. We then review strategies, including composition- and additive-engineering, defect passivation, and matching charge transport layers, for enhancing the carrier diffusion length of NBG perovskite cells and mitigating voltage losses in WBG perovskite cells. We also summarize the advances made in the fabrication of PTSCs on the device level, especially the evolution of tunnel recombination junctions and tandem device architectures. Finally, we highlight further research efforts needed to overcome roadblocks to commercialization (e.g., improving the environmental, thermal, and operating stability of these devices) and offer our perspective on the future development of this rapidly advancing field.

Numerical simulation of highly efficient lead-free all-perovskite tandem solar cell

The numerical simulation of lead-free all-perovskite tandem solar cell using solar capacitance one dimensional tool (SCAPS 1D) has been performed. The combination of methyl ammonium germanium halide (CH3NH3GeI3) as wide band-gap (1.9 eV) perovskite layer and FA0.75MA0.25Sn0.25 Ge0.5I3 (FAMASnGeI3) as a low band-gap (1.4 eV) perovskite layer is considered for the first time which shows the optimal device efficiency of 26.72%. The present work studies the effect of the different electron transport layer, perovskite absorber thickness and its defect density on photovoltaic performance. Further, the effect of front electrode work function on the device photovoltaic performance is also studied. It has been observed that the device open circuit voltage (VoC) is significantly affected by the built-in voltage (Vbi) across the perovskite layer. In addition, the effect of thickness of the perovskite absorber layers is also investigated. Moreover, the effect of defect density of the absorber layer is also explored, and it has been found that for better device performance the defect density needs to be as low as possible. Furthermore, it has been observed that the work function of the front contact plays a significant role and for the proposed device its value should not be more than 4.4 eV. The proposed all–perovskite tandem solar cell shows the remarkable photovoltaic parameters i.e., open circuit voltage (VOC) = 1.07 Volts, short circuit current density (JSC) = 28.36 mA/cm2, fill factor (FF) = 84.39% and efficiency (η) = 26.72%.

Simplified interconnection structure based on C60/SnO2-x for all-perovskite tandem solar cells

The efficiencies of all-perovskite tandem devices are improving quickly. However, their complex interconnection layer (ICL) structures—with typically four or more layers deposited by different processes—limit their prospects for applications. Here, we report an ICL in all-perovskite tandem cells consisting merely of a fullerene layer and a SnO2–x (0 < x < 1) layer. The C60 layer is unintentionally n-doped by iodine ions from the perovskite and thus acts as an effective electron collecting layer. The SnO2–x layer, formed by the incomplete oxidization of tin (x = 1.76), has ambipolar carrier transport property enabled by the presence of a large density of Sn2+. The C60/SnO1.76 ICL forms Ohmic contacts with both wide and narrow bandgap perovskite subcells with low contact resistivity. The ICL boosts the efficiencies of small-area tandem cells (5.9 mm2) and large-area tandem cells (1.15 cm2) to 24.4% and 22.2%, respectively. The tandem cells remain 94% of its initial efficiency after continues 1-sun illumination for 1,000 h. Interconnecting layers are critical to the efficiency of tandem solar cells and a high number of layers is typically needed to ensure good electrical properties. Yu et. al show that a fullerene/tin-oxide interconnecting layer enables 24.4% efficiency and improved stability in all-perovskite tandem solar cells.

Recent progress in developing efficient monolithic all-perovskite tandem solar cells

Organic–inorganic halide perovskites have received widespread attention thanks to their strong light absorption, long carrier diffusion lengths, tunable bandgaps, and low temperature processing. Single-junction perovskite solar cells (PSCs) have achieved a boost of the power conversion efficiency (PCE) from 3.8% to 25.2% in just a decade. With the continuous growth of PCE in single-junction PSCs, exploiting of monolithic all-perovskite tandem solar cells is now an important strategy to go beyond the efficiency available in single-junction PSCs. In this review, we first introduce the structure and operation mechanism of monolithic all-perovskite tandem solar cell. We then summarize recent progress in monolithic all-perovskite tandem solar cells from the perspectives of different structural units in the device: tunnel recombination junction, wide-bandgap top subcell, and narrow-bandgap bottom subcell. Finally, we provide our insights into the challenges and scientific issues remaining in this rapidly developing research field.

Tin and Mixed Lead-Tin Halide Perovskite Solar Cells: Progress and their Application in Tandem Solar Cells.

Metal halide perovskites have recently attracted enormous attention for photovoltaic applications due to their superior optical and electrical properties. Lead (Pb) halide perovskites stand out among this material series, with a power conversion efficiency (PCE) over 25%. According to the Shockley-Queisser (SQ) limit, lead halide perovskites typically exhibit bandgaps that are not within the optimal range for single-junction solar cells. Partial or complete replacement of lead with tin (Sn) is gaining increasing research interest, due to the promise of further narrowing the bandgaps. This enables ideal solar utilization for single-junction solar cells as well as the construction of all-perovskite tandem solar cells. In addition, the usage of Sn provides a path to the fabrication of lead-free or Pb-reduced perovskite solar cells (PSCs). Recent progress in addressing the challenges of fabricating efficient Sn halide and mixed lead-tin (Pb-Sn) halide PSCs is summarized herein. Mixed Pb-Sn halide perovskites hold promise not only for higher efficiency and more stable single-junction solar cells but also for efficient all-perovskite monolithic tandem solar cells.