The Korea Institute of Energy Research has made significant strides in the development of semi-transparent perovskite solar cell technology, achieving a world-leading efficiency of 21.68% and showcasing exceptional durability. This breakthrough, aimed at advancing solar cell applications in windows and tandem configurations, addresses critical challenges in achieving carbon neutrality by 2050. The institute’s innovative research has substantially improved the stability and efficiency of these cells, contributing significantly to the field of solar energy.
The persistent issue of metal oxide layer degradation in semi-transparent perovskite solar cells has been successfully addressed for the first time globally, marking significant progress in this burgeoning technology.
The Photovoltaics Research Department at the Korea Institute of Energy Research, in collaboration with the KIER Energy AI and Computational Science Lab, has focused on enhancing the durability and performance of semi-transparent perovskite solar cells. These cells hold promise for applications in building windows and the development of tandem solar cells.
These semi-transparent solar cells have achieved a record-breaking efficiency of 21.68%, surpassing all other perovskite solar cells using transparent electrodes globally. Additionally, they exhibit outstanding durability, maintaining over 99% of their initial efficiency after 240 hours of operation.
Aiming for Carbon Neutrality and Solar Innovation The pursuit of carbon neutrality by 2050 necessitates achieving ‘ultra-high efficiency’ and diversifying the application areas of next-generation solar cell technology. Overcoming constraints in installation spaces and national land area requires efficient and multi-functional technologies like tandem solar cells and solar cells for windows, demanding highly efficient and stable semi-transparent perovskite solar cells.
To fabricate these cells, conventional opaque solar cell metal electrodes must be replaced with transparent electrodes allowing light to pass through. However, the process generates high-energy particles leading to the degradation of the hole transport layer’s performance. The common solution involves depositing a metal oxide layer acting as a buffer between the hole transport layer and the transparent electrode layer. Yet, the charge-transporting properties and stability of semi-transparent devices are compromised compared to opaque solar cells under the same conditions, with unclear causes and solutions.
Breakthrough in Understanding and Enhancing Solar Cell Stability Researchers utilized electro-optical analysis and atomic-level computational science to identify causes of reduced charge transporting properties and stability during semi-transparent perovskite solar cell fabrication. Their findings revealed that lithium ions (Li), added to enhance the electrical conductivity of the hole transport layer, diffuse into the metal oxide layer, altering its electronic structure and degrading its characteristics.
The researchers addressed this challenge by optimizing the oxidation time of the hole transport layer, converting lithium ions into stable lithium oxide (LixOy) and mitigating their diffusion. This optimization significantly enhanced the stability of the device, showcasing that lithium oxide, considered a simple reaction byproduct, plays a crucial role in improving efficiency and stability.
The developed process resulted in semi-transparent perovskite solar cells achieving an impressive 21.68% efficiency, the highest among all transparent electrode perovskite solar cells. Furthermore, the research demonstrated an outstanding retention of over 99% of its initial efficiency for 400 hours in dark storage and more than 240 hours in continuously illuminating operational conditions, highlighting its remarkable efficiency and stability.
Implementation in Bifacial Tandem Solar Cells Taking a step further, the research team applied the developed solar cells as the top cell of tandem solar cells, creating the country’s first bifacial tandem solar cells. These cells utilize light reflected from the rear as well as that incident from the front surface. In collaboration with Jusung Engineering Co., Ltd. and the German Jülich Research Center, the bifacial tandem solar cells achieved high bifacial equivalent efficiencies of 31.5% for four-terminal and 26.4% for two-terminal configurations under conditions where the reflected light from the rear was 20% of standard sunlight.
Dr. Ahn SeJin, the leader of the research in the Photovoltaics Research Department, stated, “This study represents a significant advance in the field by examining the degradation process occurring at the interface of an organic compound and metal oxide buffer layer which is unique to semi-transparent perovskite solar cells,” and added, “Our solution is readily implementable, demonstrating great potential for the future use of the technologies we have developed.”