2. High-efficiency flexible solar cell technology

High-efficiency flexible solar cell technology

  • School of Engineering/Graduate School of Engineering

Noritaka Usami [Professor]


Outline of Seeds

Solar cells are becoming increasingly widespread as a green energy source, leading to demand for the creation of solar cells that (1) have high energy conversion efficiency to product substantial output in a compact space, (2) are lightweight and flexible enough to be installed in a variety of locations, and (3) are durable enough to withstand long-term sun exposure. Our team has created a solar cell on a flexible silicon substrate no more than 100 microns in thickness made up of elements that are plentiful in nature and using a silicide semiconductor to achieve high durability. The result is a high-efficiency, flexible solar cell.

Novelty and originality of this research

Our team also has photonic nanostructure technologies that support unique light management that can even be applied to ultrathin silicon substrates, as well as high-performance passivation technologies. We are also in the process of researching and developing barium silicide as a new semiconductor material whose contituent elements are found abundantly in nature and can be applied to the top cell. Barium silicide has great advantages across multiple solar cell applications, including band gaps, absorption coefficient, and minority carrier lifetime. We have a unique technology that uses a vacuum evaporation method with barium silicide granules, which are stable in air, as a raw material in order to get a thin silicide film on a silicon substrate in a single phase and oriented along the a-axis. Because a chemical compound is being used as the evaporation source, controlling the gas phase composition and substrate temperature are the keys to growing a high-quality thin film. By depositing a silicon thin film with high-concentration doping as well as silicon-based alloy on the substrate surface in advance, we have been able to control electronic properties as well.

Application and research area for Industry collaboration

We are moving forward with applied research on the homogenous growth of thin silicide films on large-area substrates based on insights weve gained from compact film formation equipment at the university, which has allowed us to accelerate the real-world applications of high-efficiency, flexible solar cells. With these advances, dreams of next-generation vehicles able to supply the power required for average traveling distances, the development of integrated solar cells with significant economic impact, and net-zero energy homes with zero CO2 emissions may soon become realities.

Key Takeaway

We are working to funnel our research outcomes back into society as soon as possible, and by selecting materials based on silicon (a plentiful research resource that is safe and enjoys widespread social acceptance) as our primary topic of study, we are taking steps to ensure that the end goal of what we do is clearly defined, and eagerly doing so from the earliest stages in our industrial-academic joint research as well.


Barium silicide, light management, tandem solar cells, flexible solar cells


  • Crystal growth/processing technologies (from bulk to nano scale)
  • Solar cell fabrication process and evaluation techniques
  • Techniques for evaluating the optical properties and electrical characteristics of semiconductors
  • Techniques for evaluating microstructures


  • Gas-source molecular beam epitaxy
  • plasma CVD
  • ALD
  • nanospace microscope spectrometer
  • minority carrier lifetime measurement system
  • solar simulator
  • photoluminescence imaging


  • Japanese Unexamined Patent Application Publication No. 2015-220371
  • Japanese Unexamined Patent Application Publication No. 2016-008316
  • Japanese Unexamined Patent Application Publication No. 2016-031984

Monographs, Papers and Articles

  • Exploring the Potential of Semiconducting BaSi2 for Thin-Film Solar Cell Application, Journal of Physics D: Applied Physics 50, 023001 (2017).
  • p-BaSi2/n-Si heterojunction solar cells with conversion efficiency reaching 9.0%, Applied Physics Letters 108, 152101 (2016).
  • Fabrication of single-phase polycrystalline BaSi2 thin films on silicion substrates by vacuum evaporation for solar cell applications, Japanese Journal of Applied Physics 54, 08KC03 (2015).
  • Determination of bulk minority-carrier lifetime in BaSi2 earth-abundant absorber films by utilizing a drastic enhancement of carrier lifetime by post-growth annealing, Applied Physics Express 6, 112302 (2013).