Efficient Type-II Heterojunction Nanorod Sensitized Solar Cells Realized by Controlled Synthesis of Core/Patchy-Shell Structure and CdS Cosensitization

Sangheon Lee; Joseph C Flanagan; Jaewook Kim; Alan Jiwan Yun; Byungho Lee; Moonsub Shim; Byungwoo Park

doi:10.1021/acsami.9b02873

Efficient Type-II Heterojunction Nanorod Sensitized Solar Cells Realized by Controlled Synthesis of Core/Patchy-Shell Structure and CdS Cosensitization

ACS Appl Mater Interfaces. 2019 May 29;11(21):19104-19114. doi: 10.1021/acsami.9b02873. Epub 2019 May 16.

Authors

Sangheon Lee¹, Joseph C Flanagan², Jaewook Kim¹, Alan Jiwan Yun¹, Byungho Lee¹, Moonsub Shim², Byungwoo Park¹

Affiliations

¹ WCU Hybrid Materials Program, Department of Materials Science and Engineering, Research Institute of Advanced Materials , Seoul National University , Seoul 08226 , Korea.
² Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory , University of Illinois at Urbana-Champaign , Urbana , Illinois 61801 , United States.

PMID: 31066260
DOI: 10.1021/acsami.9b02873

Abstract

Here, we report the successful application of core/patchy-shell CdSe/CdSe _xTe_{1- x} type-II heterojunction nanorods (HNRs) to realize efficient sensitized solar cells. The core/patchy-shell structure designed to have a large type-II heterointerface without completely shielding the CdSe core significantly improves photovoltaic performance compared to other HNRs with minimal or full-coverage shells. In addition, cosensitization with CdS grown by successive ionic layer adsorption and reaction further improves the power conversion efficiency. One-diode model analysis reveals that the HNRs having exposed CdSe cores and suitably grown CdS result in significant reduction of series resistance. Investigation of the intercorrelation between diode quality parameters, diode saturation current density ( J₀) and recombination order (β = (ideality factor)^-1) reveals that HNRs with open CdSe cores exhibit reduced recombination. These results confirm that the superior performance of core/patchy-shell HNRs results from their fine-tuned structure: photocurrent is increased by the large type-II heterointerface and recombination is effectively suppressed due to the open CdSe core enabling facile electron extraction. An optimized power conversion efficiency of 5.47% (5.89% with modified electrode configuration) is reported, which is unmatched among photovoltaics utilizing anisotropic colloidal heterostructures as light-harvesting materials.

Keywords: II−VI semiconductor; core/shell; cosensitization; heterojunction nanorod; sensitized solar cell.