Enhancing photo-induced ultrafast charge transfer across heterojunctions of CdS and laser-sintered TiO2 nanocrystals

Bryan Spann, Purdue University, Birck Nanotechnology Center
Venkataprasad S. Bhat, Purdue University, Birck Nanotechnology Center
Qiong Nian, Purdue University
Kelly Rickey, Purdue University, Birck Nanotechnology Center
Gary Cheng, Purdue University
Xiulin Ruan, Purdue University, Birck Nanotechnology Center
Xianfan Xu, Purdue University, Birck Nanotechnology Center

Abstract

Enhancing the charge transfer process in nanocrystal sensitized solar cells is vital for the improvement of their performance. In this work we show a means of increasing photo-induced ultrafast charge transfer in successive ionic layer adsorption and reaction (SILAR) CdS-TiO2 nanocrystal heterojunctions using pulsed laser sintering of TiO2 nanocrystals. The enhanced charge transfer was attributed to both morphological and phase transformations. At sufficiently high laser fluences, volumetrically larger porous networks of the metal oxide were obtained, thus increasing the density of electron accepting states. Laser sintering also resulted in varying degrees of anatase to rutile phase transformation of the TiO2, producing thermodynamically more favorable conditions for charge transfer by increasing the change in free energy between the CdS donor and TiO2 acceptor states. Finally, we report aspects of apparent hot electron transfer as a result of the SILAR process which allows CdS to be directly adsorbed to the TiO2 surface.

Discipline(s)

Nanoscience and Nanotechnology