About AIST > Organization > Research Center for Photovoltaics > Research Teams & Themes > Compound Semiconductor Thin Film Team

Research Center for Photovoltaics


Compound Semiconductor Thin Film Team ( CSTFT )



We clarify and determine the essential mechanisms which lead high-efficiency solar cells and develop the advanced device processing technologies to overcome the difficulties, particularly for compound semiconductor thin-film solar cells, such as CIGS and CZTS solar cells. We also introduce the developed technologies to industrial sectors, and contribute to the development of solar cell industries in Japan.


Our research target covers fundamental materials science for the development of submodule fabrication technologies. We improve the performance of the materials for light-absorbing layers and transparent electrodes, and develop various device processing technologies, such as,

  1. Improving the performance of laboratory-scale CIGS and CZTS devices up to their potential limit and applying the results to submodules,
  2. Developing novel materials as well as alternative materials for high efficiency CIGS and CZTS solar cells,
  3. Developing advanced technology to characterize materials for solar cells, and,
  4. Developing the device processing technologies to realize high efficiency CIGS and CZTS submodules, particularly for flexible solar cells.

Research Activities

(1)Improvement of the performance of laboratory-scale CIGS solar cells

We have made a number of essential reasons clear which prevent the solar cells from achieving high efficiency and obtained laboratory-scale CIGS devices with efficiency of 22%. In addition, we have developed laboratory-scale indium-free CGS devices with efficiency of 11.0 %. These results strengthen the technological prospects of CIGS solar cells with high gallium concentration, which are expected as promising solar cells in the future.

(2)Development of CIGS submodules

We have developed CIGS submodules using soda lime sheet glass as substrates and have obtained efficiency of 20.3%. The technology developed here is an important elemental technology to improve the conversion efficiency of CIGS submodules, and hence can be applied to large area CIGS modules as well as flexible CIGS modules.

(3)Improvement of the performance of laboratory-scale CZTS and solar cells

We develop laboratory-scale CZTS solar cells using Ge-doped CZTSe (CZTGSe) system. As the results, we obtained high open circuit voltage of 0.527 V and conversion efficiency of 12.32% at the alloy composition ratio of Ge/(Ge+Sn) = 0.2.

(4)Development of the technology to characterize the electronic states by inversed photoemission spectroscopy

We develop new methods to characterize the electronic states of semiconductors for photovoltaics by combining both inversed photoemission spectroscopy and photoemission spectroscopy. We can characterize both the conduction band and valence band of the sample precisely by the method.


 ⇒  recent publication list


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Fig. 1 CIGS submodule with efficiency of 20.3%.

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figure. 2 CZTGSe solar cell with efficiency of 12.32%.

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figure. 3 Fabrication apparatus of chalcogenide solar cells.

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figure.4 Inversed photoemissions pectroscopy measurement system.

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figure.5 Inversed photoemission spectra (right hand) and photoemission spectra (left hand) of CdS and single crystalline CIGS thin films.

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