Thermal Stability of Cuprous Oxide Top Cells for High-Efficiency Cu2O/Si Tandem Solar Cells |
Sara Yoshio1, Atsushi Wada1, Soichiro Shibasaki1, Naoyuki Nakagawa1, Yukitami Mizuno1, Yuya Honishi1, Kodai Wakamatsu1, Motohiro Toyota1, Takashi Yamamoto1, Junji Sano2, Kanta Sugimoto2, Maho Hayase2, Kazushige Yamamoto1 1Toshiba Corp. Research & Development Center, Kawasaki, --, Japan /2Toshiba Corp. Manufacturing Engineering Center, Yokohama, --, Japan |
We are developing highly efficient tandem solar cells that consist of a transparent cuprous oxide (Cu2O) top cell and a silicon (Si) bottom cell, with the aim of supplying the power required for automotive and other mobility applications even when installation space is limited. The power conversion efficiency (PCE) of the Cu2O top cell is 10.5% (research scale: 10×3 mm), which now exceeds the milestone efficiency of 10% required to achieve 30% efficiency with Cu2O/Si tandem solar cells. Here, we report on the cells’ durability, which we are pursuing along with increases in size and efficiency. We conducted a heat resistance test (85℃ in air) of a Cu2O top cell (size: 40×42 mm) capped with cover glass and sealed with adhesive around the perimeter. The Cu2O top cell maintained a PCE of at least 90.6% of the initial value even after 2,300 h, and the open-circuit voltage remained almost unchanged, indicating that there was no deterioration inside the cell (Cu2O layer and pn interface). Analysis of the J-V characteristics by device simulation showed that the decrease in efficiency was due to increased resistance in the transparent Al-doped ZnO surface electrode. The decrease in efficiency might have resulted from imperfections in the sealing structure. This paper is partially based on results obtained from a joint project with the New Energy and Industrial Technology Development Organization (NEDO). |