Professor Do-Kyeong Ko's research team identifies the core driving principles of next-generation optoelectronic devices

□ Professor Do-Kyeong Ko of the Department of Physics and Photon Science at the Gwangju Institute of Science and Technology (GIST, President Seung Hyeon Moon) has identified the dynamics of the energy carrier generated in the perovskite thin film depending on the thin film fabrication process.

□ Perovskite semiconductors can be fabricated through inexpensive and easy manufacturing methods, such as solution process, and, because they exhibit high light absorption and flexible material properties, they can be used as next generation thin film type solar cells *.

* Thin-film solar cells: Solar cells that are made by depositing thin-film semiconductors on cheap substrates, such as glass or stainless steel.

□ However, previous research has only verified the microscopic morphology of the perovskite thin film and that the microscopic morphology and device performance can be changed according to the manufacturing process. Research on the generation and destruction of energy carriers * that determine the performance of substantially perovskite optoelectronic devices is still insufficient. In addition, the time scale of the energy carrier behavior in optoelectronic devices is known to be so fast that it is difficult to find out by any electronic means currently available.

* Energy carriers: free particles that carry energy in matter. Typical examples are electrons and holes generated in semiconductors, which carry a charge.

□ The researchers introduced femtosecond instantaneous absorption spectroscopy, one of the femtosecond (1000 tenths of a second) laser-based optical time-resolved techniques, to investigate and measure the energy carrier behavior in perovskite film.

∘ The size, uniformity, and defect of the crystalline grain of the microstructure of the perovskite thin film can cause hot-carrier generation and relaxation in specific photo excitation conditions and directly affects the recombination pattern.

*  Hot-carrier: An energy carrier that is generated momentarily when semiconductor material absorbs energy greater than the band-gap of the semiconductor material.

∘ It is known that extracting a high-energy hot-carrier can reduce the energy loss of a solar cell element, which requires dynamical control such as increasing the duration of the hot-carrier. The results of this study show that the duration of the hot-carrier is increased when the size of the perovskite grain is large. This can be an experimental basis for controlling the performance of the photoelectric device through controlling the perovskite microstructure.

□ Professor Do-Kyeong Ko said, "Our research has identified the origin of the ultrahigh-speed behavior of energy carriers occurring in ferro-acoustic materials. This will contribute to predict the optimal structure for increasing the energy conversion efficiency of the perovskite photoelectric device."

□ The research entitled "Fabrication-Method-Dependent Excited State Dynamics in CH3NH3PbI3 Perovskite Films" was published on November 28, 2017, in Scientific Reports and was supported by the National Research Foundation of Korea (NRF) grants funded by the Korean government (MSIP) and was further supported by the “Ultra-short Quantum Beam Facility Program” through grant provided by the Gwangju Institute of Science and Technology in 2017.