Over recent years, solar power has gained significant traction as one of the most effective solutions to the growing climate crisis, driven by the need to transition away from fossil fuels and reduce greenhouse gas emissions. Photovoltaic (PV) technologies, in particular, have become central to this quest for clean and renewable energy. Traditionally, silicon-based solar cells have dominated the market due to their efficiency and relatively established manufacturing processes. However, as the demand for even more efficient, affordable, and scalable solar energy technologies continues to rise, researchers are increasingly exploring alternative materials that can offer greater performance.
Among these materials, perovskites—organic-inorganic hybrid compounds—have emerged as some of the most promising candidates for next-generation photovoltaic solutions. They offer the potential to deliver solar cells that are not only cheaper to produce but also capable of achieving high power conversion efficiencies, making them attractive alternatives to silicon-based solar cells. While perovskite solar cells (PSCs) offer numerous benefits, one of the major challenges that hinders their widespread adoption is their limited stability, especially under high temperatures and fluctuating environmental conditions. Nonetheless, recent advancements in material engineering, including the design of new self-assembled monolayers (SAMs), have offered hope for significantly improving the durability of PSCs.
The Promise of Perovskite Solar Cells
In recent years, researchers have focused extensively on enhancing the efficiency and stability of perovskite-based solar cells. These materials can be engineered with a wide range of tunable properties, enabling them to absorb light across a broad spectrum, which makes them particularly attractive for energy harvesting. Perovskite solar cells have shown impressive improvements in power conversion efficiency (PCE), one of the key metrics used to measure how effectively a solar cell can convert sunlight into usable electricity.
As of today, PSCs have reached power conversion efficiencies comparable to, and in some cases even surpassing, silicon-based cells, which have been the industry standard for decades. With efficiency records exceeding 25% in lab settings, PSCs have created significant excitement in the renewable energy sector. Their thin-film nature also allows for flexibility in their use, and they can be integrated into diverse environments, from building-integrated photovoltaics to portable solar-powered devices.
However, despite the remarkable progress in perovskite solar cell efficiency, one key barrier has yet to be overcome: their stability, particularly in the face of environmental challenges. Perovskite materials are highly susceptible to degradation under elevated temperatures, moisture, UV exposure, and mechanical stress, limiting their long-term performance in real-world conditions. The photovoltaic industry requires materials that maintain optimal performance for years to come, particularly when the temperature changes dramatically, a characteristic of daily and seasonal weather cycles.
The Role of Hole-Selective Self-Assembled Monolayers (SAMs) in PSC Stability
One factor contributing to the thermal instability of perovskite solar cells is their reliance on hole-selective self-assembled monolayers (SAMs). These SAMs are molecular films that play a critical role in perovskite devices by attracting and facilitating the transport of positive charge carriers, also known as holes. Hole-selective SAMs are typically used in perovskite solar cells to help improve charge extraction, a crucial function for achieving high efficiencies. However, conventional SAMs face significant challenges when it comes to their stability and adhesion to the perovskite surface.
The adhesion between the SAMs and the perovskite layer tends to be weak, which compromises the overall stability of the solar cell. Additionally, under high temperatures and environmental stress, these layers are prone to desorption, causing them to lose their functional integrity over time. This results in a decrease in the solar cell’s performance, and, as a consequence, perovskite solar cells tend to experience quicker efficiency losses compared to traditional silicon solar cells. To address these issues, researchers have been looking for innovative ways to improve the interfacial contact between the SAMs and perovskite surfaces to increase the thermal stability of PSCs.
A Breakthrough: The Self-Assembled Bilayer Film
To overcome these inherent limitations of conventional SAMs, a team of researchers from Xi’an Jiaotong University, Uppsala University, and other institutions has recently proposed a new approach—designing a self-assembled bilayer film. In their groundbreaking paper published in Nature Energy, the researchers showed how the bilayer structure could enhance both the adhesion strength and the thermal stability of perovskite solar cells.
The innovative bilayer film involves the covalent interconnection of a phosphonic acid SAM with a triphenylamine (TPA) upper layer. This hybrid SAM-bilayer structure introduces a polymerized network between the two layers, forming a more robust and durable film that adheres much more effectively to the perovskite surface than traditional monolayers. The process used to form this network, known as Friedel-Crafts alkylation, enables the triphenylamine layer to bind tightly with the phosphonic acid SAM, strengthening the overall adhesion and preventing the layers from detaching or degrading when exposed to high temperatures.
According to the research team, this self-assembled bilayer shows impressive results in thermal stability, resisting degradation even when subjected to temperatures up to 100°C for prolonged periods—specifically, 200 hours of continuous exposure. The thermal stability of this bilayer allows for better performance in real-world conditions where temperature fluctuations are common, addressing one of the main limitations of current PSC technologies.
Furthermore, the introduction of the TPA upper layer also improves the interaction between the SAM and the perovskite layer, leading to a 1.7-fold increase in the adhesion energy compared to conventional SAM-perovskite interfaces. This enhanced adhesion helps to maintain a stronger connection between the two materials over time, further improving the PSC’s durability.
Performance Results: Efficiency and Stability Improvements
The researchers tested the new self-assembled bilayer in a series of practical experiments, focusing on evaluating the effects on power conversion efficiency (PCE) and long-term stability. The results were remarkable. The devices incorporating this new self-assembled bilayer achieved power conversion efficiencies exceeding 26%. These devices also demonstrated significant improvements in both short-term and long-term performance. In particular, after 2,000 hours of damp heat exposure (85°C with 85% relative humidity), the PSCs exhibited less than a 4% reduction in efficiency. Additionally, after enduring over 1,200 thermal cycles (ranging from -40°C to 85°C), the devices maintained more than 97% of their original efficiency. These results suggest that the perovskite solar cells incorporating the bilayer film are much more resistant to temperature variations than traditional PSCs and even meet the rigorous stability standards defined by the International Electrotechnical Commission (IEC 61215:2021).
This data indicates a substantial improvement in the longevity of perovskite solar cells, particularly under extreme environmental conditions, which would be crucial for their commercial and large-scale deployment. The ability to maintain efficiency in the face of temperature changes and humidity levels typically encountered in outdoor conditions is one of the key challenges facing the widespread adoption of perovskite solar cells.
Versatility and Potential for Future Research
One of the significant advantages of this new bilayer film is its versatility. The method employed to produce this bilayer is not limited to a specific set of materials but can be adapted for different self-assembled monolayer molecules and alkylating agents. This flexibility means that the approach can be extended to a wide variety of material systems, paving the way for future advancements in perovskite solar cell technology.
The researchers anticipate that this self-assembled bilayer film could play an important role in advancing perovskite-based photovoltaics as a viable and reliable energy solution in the coming years. By improving both efficiency and long-term stability, this innovation may soon help perovskite solar cells compete more effectively with silicon-based technologies, even in harsh environmental conditions. As further research builds upon these breakthroughs, perovskite-based photovoltaics could see further improvements in efficiency, cost-effectiveness, and durability.
Conclusion
In conclusion, perovskite solar cells represent one of the most exciting avenues in the development of next-generation photovoltaics, offering the potential for lower production costs and higher power conversion efficiencies compared to traditional silicon-based systems. However, for these materials to be widely adopted, solutions are needed to address their stability challenges. The self-assembled bilayer films developed by researchers at Xi’an Jiaotong University, Uppsala University, and other collaborating institutes represent a promising step toward overcoming these obstacles. Their innovation enhances both the thermal stability and long-term performance of PSCs, contributing to the broader effort to create more sustainable, efficient, and affordable solar energy solutions. With further refinement, perovskite solar cells could play a crucial role in driving the global transition toward renewable energy.
Reference: Bitao Dong et al, Self-assembled bilayer for perovskite solar cells with improved tolerance against thermal stresses, Nature Energy (2025). DOI: 10.1038/s41560-024-01689-2.