The race towards achieving carbon neutrality by 2050 demands innovative solutions in the field of renewable energy. Among these, solar cell technology plays a critical role, and advancements in efficiency and functionality are crucial for widespread adoption. In this context, semi-transparent perovskite solar cells emerge as a promising technology with the potential to revolutionize how we integrate solar energy into our built environment.

Breaking Efficiency Records With A Collaborative Effort

Researchers at the Korea Institute of Energy Research (KIER), specifically the Photovoltaics Research Department and the KIER Energy AI and Computational Science Lab, have achieved a breakthrough in the development of semi-transparent perovskite solar cells. These cells hold immense potential for applications in building windows and tandem solar cells, offering a unique combination of transparency and high energy conversion efficiency.

The research team successfully fabricated semi-transparent perovskite solar cells with a record-breaking efficiency of 21.68%, surpassing all existing perovskite solar cells utilizing transparent electrodes. This achievement is particularly noteworthy considering the inherent challenges associated with balancing transparency and efficiency in these devices. Furthermore, the cells exhibited remarkable durability, retaining over 99% of their initial efficiency after 240 hours of operation.

Addressing Challenges and Unveiling Opportunities

Achieving “ultra-high efficiency” and “diversifying application areas” are key factors in realizing the full potential of next-generation solar cell technology, as emphasized by Dr. Ahn SeJin, the leader of the research team. This necessitates overcoming limitations in installation space and national land availability. Semi-transparent perovskite solar cells, with their unique ability to integrate seamlessly into building facades and windows, offer a compelling solution to these challenges.

However, fabricating these cells presents a unique hurdle. Replacing the metal electrodes of conventional opaque solar cells with transparent alternatives, while crucial for allowing light to pass through, introduces complexities. This process can lead to the generation of high-energy particles that degrade the performance of the hole transport layer, a critical component responsible for efficient charge collection.

Revealing the Culprit and Finding the Solution

To address this challenge, researchers typically employ a metal oxide layer as a buffer between the hole transport layer and the transparent electrode. However, this approach often leads to compromised charge-transporting properties and stability in semi-transparent devices compared to their opaque counterparts. The underlying reasons for this disparity remained unclear, hindering further development.

The KIER research team employed a combination of electro-optical analysis and atomic-level computational science to shed light on the root cause of this performance decline. Their meticulous investigation revealed that lithium ions (Li), commonly added to enhance the electrical conductivity of the hole transport layer, were diffusing into the metal oxide buffer layer. This unintended migration resulted in alterations to the electronic structure of the buffer layer, ultimately compromising its functionality.

Optimizing for Efficiency and Stability

The researchers didn’t stop at identifying the problem. They devised a solution by optimizing the oxidation time of the hole transport layer. This innovative approach facilitated the conversion of lithium ions into stable lithium oxide (LixOy) through controlled oxidation. This transformation effectively mitigated the diffusion of lithium ions, preserving the integrity of the buffer layer and consequently enhancing the overall stability of the device.

This groundbreaking discovery underscores the previously overlooked potential of lithium oxide. Previously considered merely a byproduct of the reaction, lithium oxide, when properly controlled, can play a pivotal role in boosting both efficiency and stability.

Exploring Tandem Applications

The developed fabrication process yielded semi-transparent perovskite solar cells with an impressive 21.68% efficiency, surpassing all existing transparent electrode perovskite solar cells. Furthermore, these cells exhibited exceptional stability, retaining over 99% of their initial efficiency for extended periods under various conditions, including dark storage and continuous illumination.

Building upon this success, the research team ventured further by integrating the developed solar cells as the top cell in tandem solar cell configurations. This innovative approach resulted in the creation of South Korea’s first bifacial tandem solar cells, capable of harnessing both direct and reflected sunlight, significantly enhancing overall energy capture.

In collaboration with Jusung Engineering Co., Ltd. and the German Jülich Research Center, the bifacial tandem solar cells achieved remarkable bifacial equivalent efficiencies of 31.5% for four-terminal and 26.4% for two-terminal configurations under simulated real-world conditions.

Another advantage of stacking these cells with complementary solar cells is the ability to absorb different portions of the light spectrum, researchers can achieve theoretically higher conversion efficiencies compared to single-junction solar cells. This approach has the potential to revolutionize the solar energy landscape, paving the way for the development of ultra-high-efficiency solar panels.

Implications and Potential Applications

The advancements achieved by the KIER research team hold immense promise for the future of renewable energy, particularly in the context of building-integrated photovoltaics (BIPV) and tandem solar cell technology.

Building Integration: Powering the Future of Architecture

Semi-transparent perovskite solar cells offer a unique opportunity to transform building facades into active energy-generating elements. Their ability to seamlessly integrate into windows and building materials presents a plethora of advantages:

• Enhanced aesthetics: Unlike traditional opaque solar panels, these cells can be designed with varying degrees of transparency, allowing for architects to achieve desired visual effects while simultaneously generating clean energy.

• Reduced building energy consumption: By integrating these cells into windows and facades, buildings can harness solar energy to power internal lighting and appliances, thereby reducing reliance on conventional electricity sources and lowering operational costs.

• Improved thermal insulation: Depending on the material composition and design, these cells can offer additional benefits such as improved thermal insulation, contributing to energy efficiency in both heating and cooling seasons.

Beyond Building Applications: Broadening the Horizons

The potential applications of semi-transparent perovskite solar cells extend far beyond building integration. These versatile devices can be incorporated into various innovative applications, including:

• Greenhouse power generation: By strategically integrating these cells into greenhouse roofs, researchers can explore the possibility of generating clean energy within controlled environments while maintaining optimal light conditions for plant growth.

• Vehicle sunroofs and windows: Semi-transparent solar cells can be seamlessly integrated into car sunroofs and windows, potentially contributing to powering onboard electronics and extending battery life in electric vehicles.

• Consumer electronics: The incorporation of these cells into portable devices like laptops and mobile phones could enable them to partially harvest solar energy, extending their battery life and reducing reliance on conventional charging methods.

Challenges and Opportunities: The Road Ahead

While the KIER team’s research represents a significant leap forward, further advancements are necessary to fully realize the potential of semi-transparent perovskite solar cells. Key challenges include:

• Long-term stability: Ensuring long-term operational stability under various environmental conditions remains an ongoing area of research.

• Scalability: Developing cost-effective and scalable fabrication processes is crucial for widespread adoption and commercialization.

• Environmental impact: Assessing the potential environmental impact of these devices throughout their lifecycle is essential for ensuring sustainable development.

Despite these challenges, the potential benefits of semi-transparent perovskite solar cells are undeniable. Continued research and development efforts hold the key to unlocking their full potential and paving the way for a more sustainable future powered by clean and efficient renewable energy solutions.

Conclusion

The KIER research team’s groundbreaking advancements in semi-transparent perovskite solar cells represent a significant milestone in the quest for sustainable energy solutions. These versatile devices offer exciting possibilities for building integration, tandem solar cell technology, and various innovative applications. With continued research and development efforts addressing the remaining challenges, semi-transparent perovskite solar cells have the potential to revolutionize the way we generate and utilize clean energy, contributing to a more sustainable future for generations to come.