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Title: Unravelling Photocarrier Dynamics beyond the Space Charge Region for Photoelectrochemical Water Splitting

Semiconductor photoelectrodes for photoelectrochemical (PEC) water splitting require efficient carrier generation, separation, and transport at and beyond the space charge region (SCR) formed at the aqueous interface. The trade-off between photon collection and minority carrier delivery governs the photoelectrode design and implies maximum water splitting efficiency at an electrode thickness equivalent to the light absorption depth. Here, using planar ZnO thin films as a model system, we identify the photocarriers beyond the SCR as another significant source to substantially enhance the PEC performance. The high-quality ZnO films synthesized by pulsed laser deposition feature very few deep trap states and support a long photocarrier lifetime. Combined with photoelectrochemical characterization, ultrafast spectroscopy, and numerical calculations, it is revealed that engineering the exciton concentration gradient by film thickness facilitates the inward diffusion of photocarriers from the neighboring illuminated region to the SCR and, therefore, achieves a record high quantum efficiency over 80% at a thickness far beyond its light absorption depth and the SCR width. Furthermore, these results elucidate the important role of the photocarriers beyond SCR for the PEC process and provide new insight into exploring the full potential for efficient photoelectrode materials with large exciton diffusivity.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [1] ;  [3] ; ORCiD logo [3] ;  [3] ; ORCiD logo [1] ;  [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., Stony Brook, NY (United States)
  3. Stony Brook Univ., Stony Brook, NY (United States)
Publication Date:
Report Number(s):
BNL-205681-2018-JAAM
Journal ID: ISSN 0897-4756
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 9; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY
OSTI Identifier:
1438321

Zhang, Wenrui, Yan, Danhua, Appavoo, Kannatassen, Cen, Jiajie, Wu, Qiyuan, Orlov, Alexander, Sfeir, Matthew Y., and Liu, Mingzhao. Unravelling Photocarrier Dynamics beyond the Space Charge Region for Photoelectrochemical Water Splitting. United States: N. p., Web. doi:10.1021/acs.chemmater.7b00672.
Zhang, Wenrui, Yan, Danhua, Appavoo, Kannatassen, Cen, Jiajie, Wu, Qiyuan, Orlov, Alexander, Sfeir, Matthew Y., & Liu, Mingzhao. Unravelling Photocarrier Dynamics beyond the Space Charge Region for Photoelectrochemical Water Splitting. United States. doi:10.1021/acs.chemmater.7b00672.
Zhang, Wenrui, Yan, Danhua, Appavoo, Kannatassen, Cen, Jiajie, Wu, Qiyuan, Orlov, Alexander, Sfeir, Matthew Y., and Liu, Mingzhao. 2017. "Unravelling Photocarrier Dynamics beyond the Space Charge Region for Photoelectrochemical Water Splitting". United States. doi:10.1021/acs.chemmater.7b00672. https://www.osti.gov/servlets/purl/1438321.
@article{osti_1438321,
title = {Unravelling Photocarrier Dynamics beyond the Space Charge Region for Photoelectrochemical Water Splitting},
author = {Zhang, Wenrui and Yan, Danhua and Appavoo, Kannatassen and Cen, Jiajie and Wu, Qiyuan and Orlov, Alexander and Sfeir, Matthew Y. and Liu, Mingzhao},
abstractNote = {Semiconductor photoelectrodes for photoelectrochemical (PEC) water splitting require efficient carrier generation, separation, and transport at and beyond the space charge region (SCR) formed at the aqueous interface. The trade-off between photon collection and minority carrier delivery governs the photoelectrode design and implies maximum water splitting efficiency at an electrode thickness equivalent to the light absorption depth. Here, using planar ZnO thin films as a model system, we identify the photocarriers beyond the SCR as another significant source to substantially enhance the PEC performance. The high-quality ZnO films synthesized by pulsed laser deposition feature very few deep trap states and support a long photocarrier lifetime. Combined with photoelectrochemical characterization, ultrafast spectroscopy, and numerical calculations, it is revealed that engineering the exciton concentration gradient by film thickness facilitates the inward diffusion of photocarriers from the neighboring illuminated region to the SCR and, therefore, achieves a record high quantum efficiency over 80% at a thickness far beyond its light absorption depth and the SCR width. Furthermore, these results elucidate the important role of the photocarriers beyond SCR for the PEC process and provide new insight into exploring the full potential for efficient photoelectrode materials with large exciton diffusivity.},
doi = {10.1021/acs.chemmater.7b00672},
journal = {Chemistry of Materials},
number = 9,
volume = 29,
place = {United States},
year = {2017},
month = {4}
}