As the demand for renewable energy grows, scientists are developing new types of solar cells that are both highly efficient and scalable. The back-contact perovskite solar cell (BC-PSC) is one such innovative architecture, emerging as a promising alternative to traditional front-contact designs. In conventional perovskite solar cells, the electrode contacts and charge transport materials are placed on front of the device – the surface that faces the sun. Because incoming light must first pass through these layers before reaching the active perovskite material, a portion of the light is inevitably lost.
In contrast, BC-PSCs position the perovskite absorber layer at the top of the stack, allowing direct sunlight exposure, while electron and hole-collection contacts are positioned at the back. When light falls on the perovskite layer, it generates holes and electrons, which subsequently migrate to their respective transport layers to produce photocurrent. This design minimizes optical losses, enhances charge collection, and improves power conversion efficiency. However, this design introduces new challenges. Since charge carriers must travel longer distances, they are more likely to encounter interfacial defects, leading to recombination losses. This leads to reduced efficiency and stability, limiting practical application.
In a breakthrough, a research team led by Associate Professor Min Kim from the Department of Chemical Engineering, University of Seoul, Republic of Korea and Mr. Dohun Baek, a PhD student from School of Chemical Engineering, Jeonbuk National University, Republic of Korea, has developed a novel bilayer tin oxide (SnO2) electron transport layer (ETL), via a simple spin-coating method, that significantly improves efficiency and stability of BC-PSCs. The study was made available online on July 04, 2025, and published in Volume 654 of the Journal of Power Sources on October 30, 2025.
"We selected SnO2 for the ETL due to its favorable conduction band alignment with perovskite and superior electron mobility compared to conventional titanium oxide. As a result, our bilayer ETL enhances interfacial contact, reduces recombination losses, and optimizes energy alignment for electron charge carriers," explains Dr. Kim.
To evaluate the role of ETL engineering, the researchers fabricated three BC-PSC devices with different SnO2-based ETLs: a colloidal SnO2 made of nanoparticles, a sol-gel SnO2, and a bilayer SnO2 consisting of a nanoparticle SnO2 layer combined with a sol-gel layer. Each ETL was spin-coated onto indium tin oxide substrates and patterned via photolithography.
The researchers conducted a series of experiments to compare the performance of the devices. The results showed that the device with bilayer SnO2 yielded the highest average photocurrent of 33.67 picoampere (pA), outperforming the sol-gel SnO2 device at 26.69 pA and colloidal SnO2 device at 14.65 pA. Furthermore, the bilayer SnO2 device also achieved a maximum power conversion efficiency of 4.52%, highest among the three, and improved operational stability, owing to its enhanced suppression of charge recombination.
"BC-PSC devices hold great promise for a variety of applications, including flexible devices and large-area solar modules, due to their high efficiency, enhanced stability, and scalable design. We believe our findings will help accelerate the development of practical BC-PSC technologies for real-world applications while advancing sustainable energy solutions," concludes Mr. Baek.
About Jeonbuk National University
Founded in 1947, Jeonbuk National University (JBNU) is a leading Korean flagship university.Located in Jeonju, a city where tradition lives on, the campus embodies an open academic community that harmonizes Korean heritage with a spirit of innovation.Declaring the "On AI Era," JBNU is at the forefront of digital transformationthrough AI-driven education, research, and administration.JBNU leads the Physical AI Demonstration Project valued at around $1 billion and spearheads national innovation initiatives such as RISE (Regional Innovation for Startup and Education) and the Glocal University 30, advancing as a global hub of AI innovation.
Website: https://www.jbnu.ac.kr/en/index.do
About Mr. Dohun Baek
Mr. Dohun Baek is a PhD student in the School of Chemical Engineering at Jeonbuk National University. He received his M.S. in Jeonbuk National University in 2023. His research focuses on enhancing the performance of perovskite optoelectronic devices for solar cells and photodetectors.
About Associate Professor Min Kim
Dr. Min Kim is an Associate Professor in the Department of Chemical Engineering at University of Seoul. His research group focuses on developing nanostructures of organic-inorganic semiconductors for optoelectronics using perovskite. His group is also developing advanced nanomaterials and next-generation optoelectronic devices for high-performance solar cells, sensors, and flexible wearable technologies. Before coming to University of Seoul, he previously served as an Associate Professor at Jeonbuk National University. He completed postdoctoral training in Dr. Annamaria Petrozza's group at the Italian Institute of Technology. In 2014, Min Kim received a PhD from Pohang University of Science and Technology (POSTECH).
