Quantum-dot PV Cell Efficiency Reaches 20.3% With 100x Light Condensing

Mar 20, 2012
Motonobu Kawai, Nikkei Electronics

A Japanese professor achieved a cell conversion efficiency of 20.3% with an intermediate band-type quantum-dot photovoltaic (PV) cell at the time of 100x light condensing.

Yoshitaka Okada, professor at the Research Center for Advanced Science and Technology of the University of Tokyo, realized the efficiency in collaboration with the Technical University of Madrid. The details of the research results will be announced at the CPV-8 (8th International Conference on Concentrating Photovoltaic Systems), an international academic conference that will take place from April 16 to 18, 2012, in Toledo, Spain.

For an intermediate band-type quantum-dot PV cell, it is not enough to embed quantum dots. And it is necessary to confirm that they function as an intermediate band. Thus far, Okada has played a leading role in the research of intermediate band-type quantum-dot PV cells. For example, he verified for the first time in the world that current increases due to two-step light absorption via an intermediate band at room temperatures.

This time, to evaluate a cell that has been proved to be able to function as an intermediate band and applied to a light condensing system, Okada collaborated with the Technical University of Madrid, which owns facilities for evaluating light condensing systems.

As a result, he achieved a cell conversion efficiency of 20.3% at the time of 100x light condensing and 21.2% at the time of 1,000x light condensing. Okada said that it will be possible to realize a cell conversion efficiency of 35% at the time of 100x light condensing and 45% at the time of 1,000x light condensing by (1) increasing the density of quantum dots, (2) improving layer structure that lowers series resistance to deal with large current generated by light condensing and (3) improving electrode structure.