Multijunction PV Team

CO2-free electricity
Developing Ultra-High-Efficiency Solar Cells to Maximize Power Generation within a Limited Area

Multijunction SCs are conventionally used in a limited range of areas such as artificial satellites. We develop fabrication technologies to reduce the cost of these devices, as well as to reduce the weight and increase the power generation capacity of existing Si SCs.

SCs: Solar Cells

Multijunction PV Team

Research themes

  • R&D in low-cost fabrication techniques for ultra-high efficiency III-V semiconductor SCs (hydride vapor phase epitaxy)
  • Work to realize low-cost bonding technology (smart stack) for various SCs
  • R&D in lightweight and flexible CIGS SCs and minimodules
  • R&D in wide- and narrow-gap CIGS SCs for multijunction applications
  • Developments in chalcogenide energy conversion materials and devices such as SCs, radiation detectors, and water splitting hydrogen evolution

Concept for social contributions and implementation

Realizing PV-powered vehicles that drive using only electricity generated from on-vehicle solar panels, with no need for charging from the existing electric power system.

Lightweight, flexible, and highly efficient cost-effective solar cells and modules, which can be installed in places where weight restrictions are severe and surfaces are curved.

Research Team Leader / Greetings


SUGAYA Takeyoshi

Multijunction SCs featuring multiple combined cells are extremely efficient, but they have not been widely adopted due to restrictive manufacturing costs. Our Hydride Vapor Phase Epitaxy (HVPE) and smart stack technologies realize the low-cost manufacturing of multijunction SCs at an unprecedented level worldwide. We will further refine these technologies and introduce practical implementations.

SUGAYA Takeyoshi


Senior Researcher





SAI Hitoshi


MIZUNO Hidenori


SVRCEK Vladimir


KOIDA Takashi

Technical Staff

IIOKA Masayuki

Technical Staff

KATOU Shunichi

Technical Staff


Technical Staff


Technical Staff

HIGUCHI Hirofumi

Clerical Staff


Clerical Staff


Low-cost Ⅲ-Ⅳ solar cells fabricated using hydride vapor phase epitaxy (HVPE) and smart stack technology

Multijunction SCs featuring multiple combined cells are extremely efficient, but they have not been widely adopted due to their manufacturing costs. We have been working on an epitaxial growth technology known as HVPE (hydride vapor phase epitaxy) which can grow materials at a cost of around a tenth of previous methods, and smart stack technology which is a low-cost bonding technique using low-cost bottom cells such as Si or CIGS. Our target is 35% for conversion efficiency and ¥200/W for the fabrication cost. We will be able to mount these SCs on unmanned aerial vehicles and cars.

 We have achieved world record conversion efficiencies of 28.3% for HVPE grown SCs and 28.1% for CIGS based 3-junction SCs fabricated using smart stack technology.

Chalcogenide thin-film photovoltaics: applications for lightweight, flexible, and multi-junction solar cells and related energy conversion devices

CIGS (a generic term for chalcopyrite compounds consisting of Cu, In, Ga, and Se and related elements) and derivative chalcogenide-based photovoltaic (PV) thin-film solar cells and modules have numerous advantages which are different from those of conventional crystalline silicon PV technology, and thus, the development of new PV markets is anticipated. CIGS thin-film PV technology enables us to fabricate lightweight, flexible, and highly efficient solar cells and modules, which can be installed in places where weight restrictions are severe and surfaces are curved. Also, space use applications are highly likely because of the high tolerance of radiation of CIGS materials. In addition to photovoltaic solar cells and modules, a wide variety of high-performance energy conversion devices such as radiation detectors and photoelectrochemical water splitting hydrogen evolution are predicted with the use of CIGS-based materials.

To date, we have demonstrated an over 18.6% CIGS photovoltaic solar minimodule efficiency using a 17-cell monolithically interconnected structure (area: 68 cm2) on a lightweight and flexible substrate.



Selected as the Journal Cover | Performance of Hydride Vapor Phase Epitaxy-Grown GaInP Photovoltaics with Double-Sided Al-Containing Passivation Layers Under Air Mass 1.5 Global Solar Irradiation and Low-Intensity Indoor Light Irradiation (Solar RRL)

Watanabe, Y.; Makita, K.; Tayagaki, T.; , Sugaya, T.; Yamada, N., Simultaneous Photovoltaic Power Generation and Electroluminescence in Three-Terminal Tandem Solar Cells, IEEE J. Photovolt. 2024, 14, 473-479

Published MAR 25 2024

Nishinaga, J.; Kamikawa, Y.; Sugaya, T.; Ishizuka, S., Comparison of polycrystalline and epitaxial Cu(In, Ga)Se2 solar cells with conversion efficiencies of more than 21%, Sol. Energy Mater. Sol. Cells 2024, 269, 112791

Published FEB 28 2024

Makita, K.; Mizuno, H.; Kamikawa, Y.; Oshima, R.; Shoji, Y.; Takamoto, T.; Ishizuka, S.; Sugaya, T., Large-Area GaAs-Based Multijunction Solar Cells by “Smart Stack” Approach Using Pd Nanoparticle Array and Silicone Adhesive, Sol. RRL 2024, 8, 2400012

Published FEB 19 2024