Professor Ji-Hee Kim and Professor Young-Hee Lee's Research Team 

Drive 3^rd Generation High-Efficiency Solar Cell Development 

by Implementing Photoelectronic Current Amplification
- published online on March 4 (Wed.) in Advanced Materials

Professor Ji-hee Kim of SKKU’s Department of Energy Science and Professor Young-hee Lee of the Nanostructure Physics Research Group (first author: Seong-tae Kim, student of the Department of Energy Science) succeeded in attaching a single quantum dot to an atomic microscope probe and amplifying the light current of a shining light.

In general, only a grain of light (photon) can produce a pair of charge carrying particles (carriers). Since the extra light energy is released into heat, it is difficult to convert all of the solar energy into electricity. Under certain conditions, however, the carrier amplification phenomenon, which generates two or more carriers instead of transmitting heat from extra energy of a pair of electron hole (carriers) generated by a single photon, has been noted as a key to significantly improve the efficiency of third-generation solar cells.

Although quantum dots are expected to have high carrier amplification efficiency without heat loss because the energy level can be separated to suppress electron-phonon scattering, optical measurement methods used previously to identify carrier amplification phenomena have limited applications in devices such as solar cells. Also, it was difficult to accurately analyze the carrier amplification phenomenon that occurred in one quantum dot, as conventional measurement methods allowed the study of carrier amplification only on solutions that dispersed quantum dots or even quantum dot film specimens.

Therefore, the researchers devised a method of re-extracting optical carriers generated by atomic microscopes, measuring them with photovoltaic currents, and observing current changes in amplified carriers within a single quantum point.

The researchers attached a sulphurized quantum dot to the apex of an atomic microscope conductive probe and accurately approached a graphene electrode with quantum dots within tens of nanometers to achieve small contact resistance and short channel distances. This structure is a vertical junction structure similar to thin-film solar cells, which enables control of the recombination rate of electron holes and can generate local light currents by increasing carrier extraction efficiency. The quantum efficiency extracted from the measured local light current reached 99%, the highest efficiency of the quantum dot carrier amplification reported to date, and achieved the lowest carrier amplification critical energy.

The photoelectric amplification using atomic microscopy developed by the research team is a new and unique evaluation technology that can directly evaluate the photoelectric amplification phenomenon in low-dimensional devices. It is expected that it will secure leading infrastructure technology in developing third-generation high-efficiency solar cells that utilize photoelectric amplification in the future and will serve as a foundation for creating new industries.

This paper was published online on March 4 (Wed.) in Advanced Materials (Effectiveness Index=25.809) which is within the top 2% of international journal rankings in applied physics.