Chitose Sada

Fundamental Properties of Titanium-Doped Indium Oxide and Its Application to Thin-Film Silicon Solar Cells

We have investigated the fundamental optoelectronic properties of newly developed transparent conductive oxide (TCO) materials, e.g., titanium-doped indium oxide (InTiO). InTiO films, being deposited at 50 °C by the RF-magnetron-sputtering method followed by thermal annealing at 200 °C, show excellent optoelectronic properties for solar-cell application. We have demonstrated the improved photovoltaic performance of n–i–p microcrystalline-silicon (µc-Si:H) solar cells whose i layer is prepared at a high rate of 2.3 nm/s using a stacked structure of InTiO with aluminum-doped zinc oxide (AZO) as top (front) TCO layers.

Importance of Starting Procedure for Film Growth in Substrate-Type Microcrystalline-Silicon Solar Cells

The starting procedure of hydrogenated microcrystalline-silicon (µc-Si:H) film growth at a high rate has been controlled in a plasma-enhanced chemical vapor deposition process to improve the optoelectronic properties of the resulting n/i interface as well as the intrinsic bulk layer in µc-Si:H-based substrate-type (n–i–p) solar cells. The electron temperature, monitored using optical emission spectroscopy, in the plasma during film growth is successfully controlled by changing the starting procedure, i.e., gradual SiH4 introduction and slow power application, leading to the preparation of high-quality µc-Si:H films with a low dangling-bond defect density. Reduction of the defect density in the intrinsic layer and improvement of the optoelectronic properties at the n/i interface are demonstrated through the fabrication of single-junction n–i–p solar cells showing high photovoltaic performance.

Control of electron temperature in SiH4/H2 plasma for obtaining high photovoltaic performance in microcrystalline silicon solar cells

We have proposed two novel processes for the formation of fine n/i interface to improve the photovoltaic performance in substrate-type (n-i-p type) hydrogenated microcrystalline-silicon (?c-Si:H) solar cells whose i layer is deposited at high growth rate of > 2.0 nm/sec; (1) gradual monosilane-(SiH4)-molecule-introduction method and (2) amorphous silicon (a-Si:H) thin-layer-insertion method. When applying these two methods to the formation process of n/i interface in the solar cells, drastic improvement of the production reproducibility has been achieved in the fabrication process of high efficiency (> 9%) substrate-type ?c-Si:H solar cells.