Tokyo Institute of Technology · Engineering
Professor Shinsuke Miyajima's research lab specializes in advanced thin-film materials and heterojunction devices for next-generation photovoltaics. The lab focuses on developing high-quality wide-bandgap semiconductors—such as hydrogenated aluminum oxide, nanocrystalline silicon carbide, and perovskite/silicon tandem structures—for efficient, low-temperature processed solar cells. Key research directions include surface passivation, transparent conductive emitters, photon management in thin silicon, and tunnel recombination junctions for monolithic tandem devices. The lab combines materials synthesis, advanced characterization, and device simulation to achieve high efficiency and stability in silicon-based photovoltaics.
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We investigated hydrogenated aluminum oxide (a-Al1-xOx:H) as a high quality rear surface passivation layer of crystalline silicon solar cells. The a-Al1-xOx:H films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using a mixture of trimethylaluminum (TMA), carbon dioxide (CO2), and hydrogen (H2) at a low substrate temperature of about 200 °C. The ratio of CO2 to TMA during deposition and thermal annealing after the film deposition are the key factors in achieving high quality
We developed a highly transparent n-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C–SiC:H) emitter for crystalline silicon (c-Si) heterojunction solar cells. A low emitter saturation current density (J0e) of 1.4×101 fA/cm2 was obtained under optimal deposition conditions. A c-Si heterojunction solar cell fabricated on a p-type c-Si wafer without texturing showed an active area efficiency of 17.9% [open-circuit voltage (Voc)=0.668 V, short-circuit current density (Jsc)=36.7 mA/cm2,
Undoped, n- and p-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C–SiC:H) films were successfully deposited on glass and silicon substrates at a low substrate temperature of about 300 °C by hot-wire chemical vapor deposition. The structural, optical, and electrical properties of the films were investigated by X-ray diffraction (XRD), Fourier transform infrared absorption (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsomet
Highly conductive n-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) films have been deposited by hot-wire chemical vapor deposition at low temperatures below 300 °C. We found that hexamethyldisilazane is an effective dopant for n-type doping into nc-3C-SiC:H films. Dark conductivity and its activation energy for the n-type nc-3C-SiC:H film were found to be 5.32 S/cm and 25 meV. We also fabricated nc-3C-SiC:H/crystalline silicon heterojunction diodes and solar cells. These d
We investigate perovskite/heterojunction crystalline silicon monolithic tandem solar cells by using device simulation. A hydrogenated amorphous and microcrystalline silicon‐based tunnel recombination junction is applied to the tandem solar cells. The influence of the conduction and valence band offset between the n‐type layer of the perovskite top cell and the tunnel recombination junction was investigated. To obtain excellent solar cell performance, the conduction band offset should be 0–0.6 eV
Stoichiometric hydrogenated microcrystalline cubic silicon carbide (µc-3C-SiC:H) films were successfully deposited by hot wire chemical vapor deposition (HWCVD) at a substrate temperature of 280°C using monomethylsilane and hydrogen. The ratio of hydrogen to monomethylsilane (hydrogen dilution ratio) strongly affected the structural and electrical properties of µc-3C-SiC:H films. Subgap absorption measurements on the films revealed that the defect density of the films was influenced by hydrogen
We have developed a simulation model for a heterojunction crystalline silicon (HJ-c-Si) solar cell with an n-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) emitter and a p-type hydrogenated microcrystalline silicon oxide back surface field layer. Analyses of experimentally obtained solar-cell performance using the simulation model indicate that the conversion efficiency of the solar cell is limited by the rear-surface recombination velocity (Sr) and acceptor concentration
We have successfully deposited nanocrystalline cubic silicon carbide (nc-3C-SiC:H) films at a low substrate temperature of 360 °C by very high-frequency plasma-enhanced chemical vapor deposition using monomethylsilane and hydrogen. Spectroscopic ellipsometry revealed that the crystalline volume fraction of the films increased from 69 to 92% with increasing hydrogen dilution ratio from 100 to 500. We found that the dark conductivity of the films was strongly affected by the crystalline volume fra
Passivation quality of hydrogenated amorphous aluminum oxide (a-Al1-xOx:H) films were investigated for the rear side passivation layer of c-Si solar cells using a p-type wafer. a-Al1-xOx:H films were deposited by plasma enhanced chemical vapor deposition (PECVD) using a mixture of trimethylaluminum (TMA), carbon dioxide (CO2) and hydrogen (H2) at a low substrate temperature of about 200oC. Gas flow ratio of CO2/TMA influences film properties of a-Al1-xOx:H films and is a key factor to realize hi
The effect of plasma power on the structural properties of hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) films deposited by very high frequency plasma-enhanced chemical vapor deposition was investigated. The film structure was strongly influenced by the plasma power due to the change in atomic hydrogen density in the vapor phase. A high plasma power of above 170 W (2.17 W/cm2) is required for depositing nc-3C-SiC:H films.
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