Study of multi-band solar cells using dilute nitride semiconductors

2019 Fiscal Year Final Research Report

• Project/Area Number: 16H05895
• Research Category: Grant-in-Aid for Young Scientists (A)
• Allocation Type: Single-year Grants
• Research Field: Design and evaluation of sustainable and environmental conscious system
• Research Institution: Saitama University
• Principal Investigator: Yagi Shuhei 埼玉大学, 理工学研究科, 准教授 (30421415)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 中間バンド型太陽電池 / 希釈窒化物混晶半導体

Outline of Final Research Achievements

This research was conducted for the purpose of developing high-efficiency intermediate-band (multi-band) solar cells based on a superlattice in which nitrogen delta-doped layers are inserted into a host material such as GaAs.
Samples with various alloy compositions and superlattice parameters were fabricated by MBE. They revealed the dependence of the band edge energy on the structural parameters. Physical characteristics important for designing the solar cell such as electron mobility and absorption coefficient were also obtained.
Fabricated cell showed current generation originating from two-step optical transitions via the intermediate band under two wavelength light illumination. It was found that designing a carrier blocking layer to optimize carrier accumulation in the intermediate-band and carrier extraction from the conduction band is important to enhance the current generation via the two-step optical transition.

Free Research Field

半導体工学

Academic Significance and Societal Importance of the Research Achievements

太陽電池の変換効率を向上することはモジュールコスト削減や利用用途の拡大に有効であり、地球規模の環境保護の点から求められている太陽光発電の大規模普及の促進に資する。本課題では、複数バンドギャップ間の光学遷移を利用して変換効率を高める、中間バンド型太陽電池を対象に研究を行った。これまで量子ドット積層配列で形成される超格子ミニバンドを中間バンドとする方式が主流であったが、本研究では希釈窒化物半導体材料のもつ特異なバンド構造を利用することで、中間バンドの状態密度をより高め、動作上重要な2段階の光吸収の増強を試みた。特に窒素添加手法にδドープ技術を応用することで、材料品質や組成分布の制御性を改善した。