Prof Hidefumi AKIYAMA

Prof Hidefumi AKIYAMA

Solid State Physics (ISSP), University of Tokyo, Japan

Absolute electroluminescence measurements and radiative-efficiency analysis on high-efficiency solar cells

Absolute electroluminescence (EL) measurements provide a way to evaluate internal properties of individual subcells in multi-junction (MJ) solar cells. To establish methodology of absolute EL measurements for solar-cell characterizations, we studied accuracy of the measurement by comparing independently calibrated absolute EL methods and by evaluating uncertainty of individual methods. The results showed good quantitative agreements within 10% discrepancy among the individually calibrated methods. The absolute EL measurement methods were then applied not only to evaluation of subcells internal voltages, but also to quantitative studies on subcells radiation damages and resulted internal radiative efficiency representing materials quality in MJ solarcells. They were also applied to diagnosis of multiple-quantum-well solar cells with distributed Bragg reflector mirrors, clarifying the advantages of such advanced structures. After the internal radiative efficiency of realistic subcell materials were evaluated, the detailed-balance theory was used to re-analyze the optimized MJ cell designs and the efficiency limit in the presence of non-radiative loss. 


Hidefumi AKIYAMA is a professor in the Institute for Solid State Physics (ISSP), University of Tokyo, where he has studied physics of solar cells, short-pulse generations in gain-switched semiconductor lasers, quantum-wire semiconductor lasers, solid-immersion micro-spectroscopy, and firefly bioluminescence. He received doctoral degree in physics from University of Tokyo in 1991. In 1996, and in 2000-2001, he visited Bell Labs, Lucent Technologies, as a consultant, for optical study of T-shaped quantum-wire lasers. He authored or co-authored more than 200 technical papers and 13 patents. He is a member of the Physical Society of Japan, the Japan Society of Applied Physics, and the American Physical Society.