SKKU develops ultra-low-defect semiconductor thin films through eutectic engineering, enabling both solar cells and LEDs

Sungkyunkwan University External Affairs Division (PR team)

A research team led by Professor Seong Sik Shin of the SKKU Advanced Institute of Nanotechnology (SAINT) at Sungkyunkwan University (SKKU), in international collaboration with the Korea Research Institute of Chemical Technology (KRICT), the University of California, San Diego, and Princeton University, has developed a next-generation perovskite semiconductor thin film with dramatically reduced defects. Using the same material platform, the researchers successfully demonstrated both high-performance solar cells and LEDs.

Perovskites have attracted considerable attention as key materials for next-generation electronic devices because of their low manufacturing costs and relatively simple processing. They can be used in solar cells that convert light into electricity as well as LEDs that convert electricity into light. However, when a liquid precursor solution is solidified into a thin film, microscopic crystal grains form and join together, often creating numerous defects at grain boundaries and surfaces. These defects can trap or eliminate photo-generated charge carriers, significantly reducing device performance and operational lifetime.

The research team found a solution in the eutectic phenomenon, in which the melting temperature of a mixture becomes substantially lower than that of its individual components. The researchers focused on the fact that when two materials with relatively high individual melting temperatures—methylammonium chloride (MACl) and a zinc halide (ZnX₂)—are combined, the mixture begins to melt at a much lower temperature.

When the perovskite film was gently heated to around 100°C, the mixture located at the grain boundaries transformed into a thin liquid layer. In the liquid state, atoms can diffuse approximately 10,000 times faster than in a solid, allowing small crystal grains to rapidly merge and grow into larger, cleaner crystals with fewer defects. MACl, which facilitates crystal growth, subsequently evaporates during thermal annealing, while the remaining zinc segregates toward the grain boundaries and helps suppress defects.

The resulting films demonstrated the highest level of quality reported to date for perovskite thin films. The charge-carrier lifetime reached approximately 295 μs, among the longest ever reported, while the surface recombination velocity, which indicates carrier losses caused by surface defects, was reduced to 0.3 cm/s, the lowest reported value for lead halide perovskites. This performance is comparable to the best values reported for passivated silicon.

Solar cells fabricated using the new films achieved a high power conversion efficiency of 26.5% (certified 25.9%), together with an open-circuit voltage of 1.208 V, a certified record for solar cells with the same n-i-p architecture. Remarkably, an LED with the same device architecture as the solar cell achieved an external quantum efficiency of 26.1%, demonstrating that a single device structure can function both as a power-generating device that absorbs light and as a light-emitting device.

Dr. Seongsik Nam, co-first author of the study, said, “We reduced the surface recombination velocity to 0.3 cm/s, the lowest reported for perovskite thin films, demonstrating that solution processing can achieve surface quality comparable to that of silicon. As we have also demonstrated strong performance over large areas, we expect this technology to help accelerate the commercialization of perovskite solar cells.”

Professor Seong Sik Shin, who led the research, said, “This study is the world’s first to develop a crystal-growth method based on a volatile eutectic mixture that fundamentally reduces defects in perovskites. Beyond realizing both a highly efficient solar cell and an LED within a single device architecture, the process requires no expensive specialized equipment.”

He added, “We expect this approach to find broad applications not only in various optoelectronic devices, including displays and photodetectors, but also across the wider field of materials science.”

The study was jointly led by corresponding authors Professor Seong Sik Shin of Sungkyunkwan University, Professor David P. Fenning of the University of California, San Diego, and Professor Dane W. deQuilettes of Princeton University. Dr. Seongsik Nam of Sungkyunkwan University, Dr. Jason J. Yoo of the Korea Research Institute of Chemical Technology, and Dr. Connor J. Dolan of the University of California, San Diego participated as co-first authors.