Efficiency enhancement of PbS colloidal quantum dot/ZnO nanowire solar cells in the near-infrared region and long-term stability
Haibin Wang a, Takaya Kubo a, Jotaro Nakazaki a, Hiroshi Segawa a b
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Poster, Haibin Wang, 024
Publication date: 7th November 2016

Colloidal quantum dots (CQDs) give unique optical properties such as the size dependent absorption, which makes the quantum dots promising candidate materials toward high efficiency solar cells.  In particular, PbS CQD-based solar cells of depleted heterojunction structures showed high power conversion efficiency (PCE) over 11.3 % in 2016.  However, the short exciton and / or carrier diffusion lengths of PbS QD films limit the PbS QD active layer thickness, thereby limiting light harvesting efficiency.  Thus we focused on solar cells composed of PbS CQD/ZnO nanowire structures to achieve efficient carrier transport and light absorption in the near infrared region.  After some morphology control of the ZnO nanowire arrays, we achieved external quantum efficiency (EQE) values of approximately 60% at the first exciton peak (1020 nm) and over 80% in the visible region (J. Phys. Chem. Lett., 2013, 4, 2455).  To clarify the exact role of the ZnO NW in the PbS QD/ZnO NW solar cells, we studied photocurrent properties of the solar cells by focusing on the cell structure, and found out that, ZnO NWs act as a very efficient transporter and collector for the photogenerated electrons in the PbS QD region.  Therefore, once good electron pathways was established by incorporating ZnO NWs, holes in the PbS QD region can diffuse a distance over 1000 nm (J. Phys. Chem. C., 2015, 119, 27265).  Ensuring long-term durability of the solar cells is essential for practical applications.  Long-term stability tests under quasi-sunlight illumination were performed on the PbS QD/ZnO-NW solar cells without encapsulation.  The power conversion efficiency after 3000 hour illumination maintained approximately 90% of the initial value (Phys. Status Solidi RRL, 2014, 8, 961).

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