Application of heterojunction to Si-based solar cells using photonic nanostructures coupled with vertically aligned Ge quantum dots

• Published in: Japanese Journal of Applied Physics 2015-08, Vol.54 (8S1), p.8
• Main Authors: Takahashi, Isao, Hoshi, Yusuke, Tayagaki, Takeshi, Oikawa, Takafumi, Ohdaira, Keisuke, Usami, Noritaka
• Format: Article
• Language: English
• Subjects: Carriers; Germanium; Heterojunctions; Nanostructure; Photonics; Photovoltaic cells; Quantum dots; Solar cells
• ISSN: 0021-4922; 1347-4065
• DOI: 10.7567/JJAP.54.08KA06

We have recently developed a new structure for solar cells that consists of photonic nanostructures coupled with vertically aligned Ge quantum dots on a crystalline Si substrate. For the fabrication of a solar cell device, a heterojunction with a-Si:H was chosen because its processing temperature is less than 200 °C, at which point Ge atoms cannot diffuse into Si layers. In this study, we developed a guideline for the most appropriate cell structures to take advantage of the Ge layer by fabricating heterojunction solar cells with various structures. As a result, we confirmed that the carriers absorbed in Ge quantum dots contributed output current when Ge quantum dots are fabricated on the pn-junction side. Hence, the presence of built-in potential in a Ge dot layer was found to be necessary to extract the carriers generated in the Ge layer. In addition, carrier transport in Ge quantum dots is improved under conditions of reverse bias. Therefore, the electrical field in the Ge layer is a key parameter to improve solar cell performance in our proposed structure.