RESEARCHORGANIC PV
Figure 1: Photoelectric conversion of near-infrared light using charge-transfer photo-absorption
34
As the findings enable the utilization of near- infrared light that has been a crucial subject in the R&D of OPCs, the new concept is expect to improve the efficiency of OPCs.
Figure 2
Optical absorption spectra of a single component molecular semiconductor and a molecular compound semiconductor
Social Background of Research OPCs are now intensively studied in the world because of their advantages over silicon-based solar cells in the capability of producing light- weight and flexible solar cell sheets. In addition, as OPCs can be manufactured in the process neither under vacuum nor with high temperature, it is feasible to realize the large-area and low-cost cells. The feature is expected as a key technology to realize the green innovation for the low-carbon
society. The efficiency of OPCs has reached about 7~8% in the past few years, although the further improvement in the conversion efficiency should be necessary for the practical use. The factors hindering the improvement in the efficiency include (1) a limited wavelength range of optical absorption, i.e. visible light (wavelength < 800 nm), which results in the inactivity of OPCs to near- infrared light that holds about 40% of the total solar radiation energy and (2) an extremely short lifetime of photo-excited states, which results in the large energy loss before the photoelectric conversion.
These problems originate from the inherent nature of organic semiconductors, i.e. the excitonic states are strongly confined to the individual molecules. Consequently, it is considered to be quite difficult to give fundamental solutions to these problems.
History of Research At AIST, researchers have been developing a new type of OPC that is based on the optical absorption due to the charge-transfer arisen between different molecules. Since the wavelength region of the charge-transfer optical absorption varies depending on the combination of the molecules, it becomes possible to use near- infrared light for photovoltaic conversion that is impossible for conventional organic materials.
www.solar-pv-management.com Issue I 2011
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48