1. Co-sensitized quantum dot solar cell based on ZnO nanowire a. J. Chena, J. Wua, W. Leia, b. J.L. Songb, W.Q. Dengb, c. X.W. Sunc a School of Electronic Science and Engineering, Southeast University, Sipai Lou 2#, JinLing Yuan 109, Nanjing 210096, China b Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Science, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore c School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore Speaker ： H. C. Chen Advisor ： H. C. Kuo 1 Applied Surface Science 256 (2010) 7438–7441

2. Outline  Introduction  Experiment  Results and Discussion  Conclusions 2

3. Introduction  CdS and CdSe QDs co-sensitized solar cell based on ZnO nanowire were studied in this work.  The co-sensitized structure has better performance than the single CdS or CdSe sensitized solar cell.  The power conversion efficiency of 1.42% is achieved for ZnO based CdS/CdSe co-sensitized solar cell  Electrochemical impedance spectroscopy (EIS) measured demonstrates that the electron lifetime for ZnO/CdS/CdSe (13.8 ms) is calculated longer than that of ZnO/CdS device (6.2 ms). 3

4. Experiment  ZnO nanowire was grown by a hydrothermal method at 95 ◦ C.  The chemical bath deposition (CBD) method was used to assemble CdS QDs onto ZnO film.  ZnO film with CdS QDs immersed into pre-synthesized CdSe ethanol solution for 6 h.  The ZnO/CdS and ZnO/CdS/CdSe photoelectrodes were assembled with a 20 nm platinum-coated indium tin oxide (ITO) substrate as the counter electrode.  They measured I-V curve, EQE, and EIS to analyze this cell. 4 electrolyte ITO Zno/Cds/CdSe

5. Results and Discussion  It can be seen that the optical range of ZnO/CdS/CdSe is broader than ZnO/CdS and ZnO/CdSe.  Both the conduction and valence bands positions of the three materials increase in the order: ZnO < CdS < CdSe, which is benefit for the electrons to transfer. 5

6. Results and Discussion – SEM & TEM 6 ZnO nanostructure consists of nanorod array on the bottom and the finer wires with 50nm in diameter and 9–10 µm length on the top.

7. Results and Discussion – J-V curve  The higher performance of ZnO/CdS/CdSe is attributed to its broader light absorption range which leads to a higher photocurrent. 7

8. Results and Discussion - EIS  The electron lifetime is calculated to be 6.2 and 13.8ms for ZnO/CdS and ZnO/CdS/CdSe device.  It is possibly due to the better coverage of ZnO/CdS/CdSe photoelectrode 8

9. Conclusions  ZnO/CdS/CdSe has a better performance than ZnO/CdS, which is attributed to its broader light absorption range and better coverage of QDs on ZnO nanowires.  EIS measured demonstrated longer electron lifetime for ZnO/CdS/CdSe than ZnO/CdS.  A PCE of 1.42% was achieved for ZnO/CdS/CdSe, which accounts for 54% improvement compared to ZnO/CdS device. 9

10. Thanks for your attention~ 10