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, Chinab Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Science, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singaporec School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798, Singapore

Speaker： H. C. Chen Advisor： H. C. Kuo

Applied Surface Science 256 (2010) 7438–7441

2

Outline

Introduction Experiment Results and Discussion Conclusions

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).

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.

electrolyteITO

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.

6

Results and Discussion – SEM & TEM

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.

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

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.

10

Thanks for your attention~