A supramolecular approach to improve the performance and operational stability of all-perovskite tandem solar cells – Nature

 

Report on Supramolecular Engineering for High-Performance All-Perovskite Tandem Solar Cells

Executive Summary

This report details a novel supramolecular engineering strategy to enhance the performance and operational stability of wide-bandgap (WBG) perovskite solar cells (PSCs), a critical component in next-generation tandem solar cells. The intrinsic instability of WBG perovskites, primarily caused by vacancy defects and ion migration, poses a significant barrier to their commercial viability and contribution to global energy goals. By incorporating an ether ring super-molecule, dibenzo-30-crown-10 (DB30C10), into the perovskite structure, this research demonstrates effective control over crystallization kinetics and suppression of halide segregation under illumination. This advancement directly supports the achievement of Sustainable Development Goal 7 (Affordable and Clean Energy) by improving the efficiency and durability of solar technology. The engineered 1.77 eV perovskite solar cells achieved a power conversion efficiency (PCE) of 21.01% and maintained 95% of this initial efficiency after 1000 hours of continuous operation. When integrated into a two-terminal all-perovskite tandem configuration, a champion efficiency of 28.44% (certified at 27.92%) was recorded. This work establishes a promising pathway for developing high-quality, stable mixed-halide WBG perovskites, accelerating the transition to a sustainable energy future.

Introduction: Advancing Solar Technology for Sustainable Development

The global transition to renewable energy is paramount for addressing climate change and achieving sustainable development. Perovskite solar cells (PSCs) represent a promising next-generation photovoltaic technology due to their potential for high efficiency and low production cost. Tandem solar cells (TSCs), which utilize a wide-bandgap (WBG) perovskite top cell, are capable of surpassing the efficiency limits of single-junction cells, making them a key area of innovation.

The Challenge: Instability in Perovskite Solar Cells

Despite their high potential, WBG PSCs suffer from significant degradation under operational stimuli like light and heat. The primary challenges include:

• Ion Migration: The soft lattice structure of mixed-halide perovskites allows for the migration of halide anions (iodine and bromine), leading to phase segregation.
• Vacancy Defects: The migration of ions creates defects that act as non-radiative recombination centers, trapping photogenerated carriers and reducing the cell’s voltage and overall efficiency.
• Performance Degradation: These instabilities result in a rapid decline in photovoltaic performance and limit the operational lifetime of both WBG PSCs and the tandem devices they enable.

Alignment with Sustainable Development Goals (SDGs)

Overcoming these challenges is critical for leveraging solar technology to meet several UN Sustainable Development Goals. This research directly contributes to:

1. SDG 7 (Affordable and Clean Energy): By increasing the efficiency and operational stability of solar cells, this work makes clean energy more reliable and economically competitive, facilitating universal access to sustainable energy.
2. SDG 9 (Industry, Innovation, and Infrastructure): The development of a novel supramolecular engineering approach represents a significant scientific innovation that can foster a new generation of resilient and sustainable industrial processes for photovoltaic manufacturing.
3. SDG 13 (Climate Action): Enhancing the performance of solar technology provides a more effective tool to combat climate change by accelerating the displacement of fossil fuels with carbon-free energy sources.

Methodology: A Supramolecular Engineering Approach

To address the instability of WBG perovskites, this study employed a host-guest chemical strategy using a macrocyclic ether, dibenzo-30-crown-10 (DB30C10), as a molecular additive in the perovskite precursor solution.

Material Selection and Rationale

The DB30C10 molecule was selected for its unique properties:

• Large Cavity Size: The large, oxygen-rich ether ring is capable of forming stable complexes with multiple cations present in the perovskite (formamidinium FA+, cesium Cs+, and lead Pb2+).
• Strong Coordination: Density functional theory (DFT) calculations confirmed superior adsorption energies between DB30C10 and the perovskite cations, indicating a strong tendency for complexation.
• Multi-functional Interaction: The molecule interacts with cations via its inner cavity and can stabilize halide anions through dipole-ion interactions and van der Waals forces, creating a more robust crystal lattice.

Mechanism of Action

The incorporation of DB30C10 modulates the perovskite film through a synergistic mechanism:

1. Defect Passivation: The crown ether complexes with uncoordinated cations, neutralizing vacancy defects that would otherwise facilitate ion migration and non-radiative recombination.
2. Inhibition of Halide Segregation: By anchoring the cations, the DB30C10 molecules create positively charged regions that attract and stabilize negatively charged halide anions, effectively suppressing their light-induced migration and preventing the formation of performance-limiting I-rich and Br-rich phases.
3. Controlled Crystallization: The additive regulates the crystal growth process, leading to more uniform, higher-quality perovskite films with fewer grain boundaries and residual impurities like PbI2.

Key Findings and Performance Metrics

The supramolecular engineering approach yielded significant improvements in film quality, device performance, and stability, directly advancing the viability of perovskite technology for meeting the targets of SDG 7 and SDG 13.

Improved Film Quality and Stability

• Suppressed Phase Segregation: In situ photoluminescence (PL) mapping confirmed that DB30C10-modified films remained stable under continuous illumination, whereas control films showed significant phase segregation.
• Reduced Defect Density: Space-charge-limited current (SCLC) measurements showed a marked reduction in both electron and hole trap densities in the modified films.
• Enhanced Durability: The modified films exhibited superior stability against humidity (retaining 82.2% of initial PCE after 120 hours at 60% RH) and heat (retaining 91.3% of initial PCE after 240 hours at 85°C).

Enhanced Photovoltaic Performance of WBG PSCs

The optimized WBG PSCs demonstrated state-of-the-art performance:

• Champion Efficiency: A PCE of 21.01% was achieved for opaque cells, with an open-circuit voltage (Voc) of 1.30 V and a fill factor (FF) of 86.18%.
• Operational Stability: The unencapsulated device retained 95% of its initial efficiency after 1000 hours of maximum power point (MPP) tracking under continuous illumination.

Breakthroughs in All-Perovskite Tandem Solar Cells

The high-performance WBG cells were integrated into all-perovskite tandem devices, showcasing their potential to push the boundaries of solar efficiency and contribute to SDG 9 through technological innovation.

1. Four-Terminal (4T) Tandem Cell: By stacking a semi-transparent WBG top cell (18.97% PCE) with a narrow-bandgap (NBG) bottom cell, a combined efficiency of 28.37% was achieved.
2. Two-Terminal (2T) Tandem Cell: A monolithic 2T tandem device achieved a champion PCE of 28.44%, with a certified efficiency of 27.92%. The well-matched current between the sub-cells underscores the effectiveness of the modification strategy.

Conclusion: Implications for the Global Energy Transition

This research successfully demonstrates that a supramolecular host-guest strategy can overcome critical instability issues in wide-bandgap perovskite solar cells. The use of DB30C10 as a molecular additive significantly enhances film quality, reduces defects, and suppresses ion migration, leading to unprecedented levels of efficiency and operational stability. The certified 27.92% efficiency for a 2T all-perovskite tandem solar cell marks a significant milestone in photovoltaic research.

These findings have profound implications for the global energy landscape. By making solar technology more efficient, durable, and reliable, this work directly accelerates progress towards SDG 7 (Affordable and Clean Energy) and SDG 13 (Climate Action). The innovative approach contributes to SDG 9 (Industry, Innovation, and Infrastructure) by paving the way for advanced manufacturing of next-generation solar technologies. This study provides a robust and scalable method to advance perovskite photovoltaics from the laboratory to real-world applications, supporting a sustainable and secure energy future for all.

Analysis of Sustainable Development Goals (SDGs) in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The research detailed in the article directly or indirectly addresses several Sustainable Development Goals by focusing on advancing solar energy technology. The primary SDGs connected to the article’s content are:

• SDG 7: Affordable and Clean Energy

  This is the most relevant SDG. The article’s entire focus is on improving the efficiency and stability of perovskite solar cells, a key technology for renewable energy generation. By developing “ultra-high-efficiency solar cells” with a “champion power conversion efficiency of 21.01%” and “outstanding operational stability,” the research contributes to making solar energy more affordable, reliable, and accessible, which is the core mission of SDG 7.

• SDG 9: Industry, Innovation, and Infrastructure

  The article embodies the principles of SDG 9 by showcasing cutting-edge scientific innovation. The development of a “supramolecular approach” to engineer perovskite films is a significant technological advancement. This work contributes to Target 9.5 (Enhance scientific research, upgrade the technological capabilities) and Target 9.4 by promoting the “greater adoption of clean and environmentally sound technologies” like high-efficiency photovoltaics.

• SDG 11: Sustainable Cities and Communities

  The article explicitly connects the technology to urban sustainability by mentioning its potential application in “building-integrated PVs (BIPVs).” This directly relates to making cities and human settlements more sustainable by integrating renewable energy generation into the urban infrastructure, which helps reduce the environmental impact of cities (Target 11.6).

• SDG 13: Climate Action

  While not explicitly mentioned, advancing solar technology is a fundamental strategy for combating climate change. By creating more efficient and cost-effective solar cells, the research helps accelerate the transition away from fossil fuels, thereby reducing greenhouse gas emissions and contributing to the broader goals of SDG 13.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the article’s focus on improving solar cell technology, the following specific SDG targets can be identified:

1. Target 7.2: Increase substantially the share of renewable energy in the global energy mix.

   The research directly supports this target. The article states, “Ever-increasing efficiency is the foremost guarantee to reduce the cost of commercialized solar cells.” By achieving higher power conversion efficiencies (up to 28.44% for tandem cells) and longer operational stability (“retaining 95% of initial efficiency after 1000 h”), the technology becomes more economically competitive with traditional energy sources, facilitating a substantial increase in the share of solar energy.

2. Target 7.a: Enhance international cooperation to facilitate access to clean energy research and technology… and promote investment in energy infrastructure and clean energy technology.

   This scientific paper is itself a contribution to the global pool of clean energy research. By publishing these findings, the authors facilitate access to new knowledge on “highly efficient and stable TSCs,” which can guide further research and investment in perovskite solar technology worldwide.

3. Target 9.5: Enhance scientific research, upgrade the technological capabilities of industrial sectors… encouraging innovation.

   The article is a direct outcome of activities described in this target. It details a novel “supramolecular approach” and a “host-guest strategy” to overcome key challenges in perovskite solar cells, such as “vacancy defects” and “halide segregation.” This represents a significant enhancement of scientific research and an upgrade to the technological capabilities within the renewable energy sector.

4. Target 11.6: Reduce the adverse per capita environmental impact of cities.

   The article’s mention of “building-integrated PVs (BIPVs)” as an application for wide-bandgap (WBG) PSCs directly links the research to this target. Integrating solar cells into building materials allows cities to generate clean energy on-site, reducing their reliance on centralized, often fossil-fuel-based, power plants and thereby lowering their overall environmental and carbon footprint.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article provides several specific, technical indicators that serve as direct measures of progress toward the identified targets, particularly in making solar technology more effective and viable.

• Power Conversion Efficiency (PCE)

  This is the most prominent indicator used throughout the article. It directly measures how effectively a solar cell converts sunlight into electricity. Higher PCE means more power from a smaller area, which is crucial for cost-effectiveness. The article quantifies this with specific values:

  • “a champion power conversion efficiency of 21.01%” for the single-junction cell.
  • “the champion efficiency of 28.44% (certified 27.92%)” for the tandem solar cell.

• Operational Stability and Durability

  This indicator measures the longevity and reliability of the solar cells, which is critical for commercial viability and reducing long-term costs. The article provides a clear metric for this:

  • The engineered solar cell retains “95% of initial efficiency after 1000 h of maximum-power-point tracking test.”
  • Improved moisture stability is shown by the contact angle increasing from 44.7° to 64.96°, indicating “that Crown increased the hydrophobicity of the perovskite films.”

• Cost Reduction (Implied)

  While the article does not provide direct cost figures, it explicitly links efficiency to cost, implying that PCE is a proxy indicator for economic viability. The statement, “Ever-increasing efficiency is the foremost guarantee to reduce the cost of commercialized solar cells,” establishes this connection. By improving efficiency and stability, the research contributes to lowering the levelized cost of solar energy.

4. Table of SDGs, Targets, and Indicators

SDGs	Targets	Indicators Identified in the Article
SDG 7: Affordable and Clean Energy	7.2: Increase substantially the share of renewable energy in the global energy mix. 7.a: Enhance access to clean energy research and technology.	Power Conversion Efficiency (PCE): Achieved 21.01% (single-junction) and 28.44% (tandem), making solar more competitive. Operational Stability: Retained 95% of initial efficiency after 1000 hours, improving long-term viability. Implied Cost Reduction: Stated that increased efficiency is the “foremost guarantee to reduce the cost.”
SDG 9: Industry, Innovation, and Infrastructure	9.5: Enhance scientific research and upgrade technological capabilities.	Technological Innovation: Development of a novel “supramolecular approach” and “host-guest strategy” to solve material instability. Improved Material Properties: Reduced defect density, suppressed halide segregation, and inhibited non-radiative recombination.
SDG 11: Sustainable Cities and Communities	11.6: Reduce the adverse per capita environmental impact of cities.	Application in Urban Infrastructure: Mention of suitability for “building-integrated PVs (BIPVs)” to create sustainable buildings.
SDG 13: Climate Action	(Implied) Strengthen resilience and adaptive capacity to climate-related hazards.	Contribution to Decarbonization: The entire research effort to advance solar technology supports the transition away from fossil fuels, which is the primary strategy for climate action.

Source: nature.com