CdSe/ZnS Quantum Dot-to-ZnO Nanowires Charge Transfer Dynamics for Enhanced Efficiency Quantum Dot-Sensitized Solar Cell
- PDF / 43,979,034 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 55 Downloads / 205 Views
CdSe/ZnS Quantum Dot-to-ZnO Nanowires Charge Transfer Dynamics for Enhanced Efficiency Quantum Dot-Sensitized Solar Cells Bahareh Sadeghimakki, Navid Mohammad Sadeghi. Jahed, Bita Janfeshan, Shadi Dashmiz and Siva Sivoththaman Center for Advanced Photovoltaic Devices and Systems (CAPDS), ECE Department, University of Waterloo, Waterloo, ON, Canada ABSTRACT Core-shell quantum dots (QDs) with enhanced photostability compared with bare QDs are promising light absorbers for solar cell applications. In this work, electron injection from excited CdSe/ZnS QDs to Zinc Oxide (ZnO) nanowires (NWs) prepared by two techniques were demonstrated. Arrays of ZnO NWs were fabricated by hydrothermal growth and etching. ZnO NWs were sensitized with hydrophobically ligated colloidal CdSe/ZnS QDs. The electron transfer dynamic in QD/ZnO NW architecture was examined using photoluminescence (PL) and decay lifetime analyses. The quenching of the QD emission peak and lowered average lifetime in QD/ZnO NW architecture confirms the deactivation of the excited QDs via electron transfer to ZnO NWs. Electron transfer was enhanced by using smaller QDs. This study provides insight on charge transfer dynamics at the QD/ZnO NW interface in order to engineer high performance quantum dot sensitized solar cells (QDSSCs). INTRODUCTION Wide-band gap metal oxide NWs sensitized with QDs is a promising structure providing a transparent medium with high surface area for the QD absorbers and a directional path for the carriers to use in photovoltaic devices such as QDSSCs [1]. Although slow hole transfer, interface carrier recombination and poor counter-electrode performance still remain as challenges in the realization of high performance QDSSCs, the charge transfer dynamics from the QDs to the NWs are also key to better performance. To date, the carrier transfer mechanisms have been explored for QDs anchored to wide bandgap materials in the form of nanoparticles, nanotubes [2, 3], and NW structures [4, 5]. In order to provide NWs with high structural, electronic and optical properties, simple and scalable process technologies are required and significant characterization studies need to be performed. In this work, we report on two simple, low cost and scalable methods of ZnO NW synthesis. In the first approach ZnO NWs were grown with a hydrothermal method. Upright NWs with a relatively high aspect ratio and perfect crystalline structure were obtained using this method. To further control the electrical properties of the wires, an alternative approach was used for ZnO NW formation by combining nanosphere lithography and etching in fluorine-based plasma. Etching in flourine-based gases is a promising technique for pattern transfer to ZnO film. Flourine is relatively easier to handle than the toxic and corrosive chloride and bromide gases that have mostly been used for ZnO etching [6]. The wires were formed on a pre-sputtered Aluminum doped ZnO layer (Al:ZnO) with sheet resistance of 30Ω/□, carrier concentration of 4×1020 cm-3 and average transparency of 85% i
