Precise surface state control of carbon quantum dots to enhance charge extraction for solar cells

Abstract

Dye‐sensitized solar cells are regarded as promising candidates to resolve the energy and environmental issues in recent years, arising from their solution‐processable fabrication technology and high power conversion efficiency. However, there are still several problems regarding how to accelerate the development of this type of photovoltaics, including the limited light‐harvesting ability and high‐production cost of molecular dye. In the current work, we have systematically studied the role of nitrogen‐doped carbon quantum dots (N‐CQDs) as co‐sensitizers in traditional dye sensitized solar cells. A series of N‐CQDs have been prepared by employing chitosan as a precursor via one‐pot hydrothermal technology for various times, demonstrating a maximized efficiency as high as 0.089% for an only N‐CQDs‐based device. Moreover, the co‐sensitized solar cell based on N719 dye (C58H86N8O8RuS2) and optimized N‐CQDs shows significantly enhanced performance, yielding a solar‐to‐electric conversion efficiency of up to 9.15% under one standard sun (AM 1.5G) irradiation, which is much higher than the 8.5%‐efficiency of the controlled device without N‐CQDs. The matched characteristics of energy level, excellent up‐convention, and FRET (Förster resonance energy transfer) abilities of N‐CQDs are responsible for their improved power conversion efficiency.