Title: Solution-Processed Zinc Oxide/Polyethylenimine Nanocomposites as Tunable Electron Transport Layers for Highly Efficient Bulk Heterojunction Polymer Solar Cells
Authors: Chen, Hsiu-Cheng
Lin, Shu-Wei
Jiang, Jian-Ming
Su, Yu-Wei
Wei, Kung-Hwa
Department of Materials Science and Engineering
Keywords: photovoltaics;conduction band;zinc oxide: polyethylenimine nanocomposites;electron transport layer;grazing-incidence small-angle X-ray scattering
Issue Date: 25-Mar-2015
Abstract: In this study, we employed polyethylenimine-doped sol-gel-processed zinc oxide composites (ZnO:PEI) as efficient electron transport layers (ETL) for facilitating electron extraction in inverted polymer solar cells. Using ultraviolet photoelectron spectroscopy, synchrotron grazing-incidence small-angle X-ray scattering and transmission electron microscopy, we observed that ZnO:PEI composite films\' energy bands could be tuned considerably by varying the content of PEI up to 7 wt %-the conduction band ranged from 4.32 to 4.0 eV-and the structural order of ZnO in the ZnO:PEI thin films would be enhanced to align perpendicular to the ITO electrode, particularly at 7 wt % PEI, facilitating electron transport vertically. We then prepared two types of bulk heterojunction systems-based on poly(3-hexylthiophene) (P3HT):phenyl-C-61-butryric acid methyl ester (PC61BM) and benzo[1,2-b:4,5-b]dithiophene-thiophene-2,1,3-benzooxadiazole (PBDTTBO):phenyl-C-71-butryric acid methyl ester (PC71BM)-that incorporated the ZnO:PEI composite layers. When using a composite of ZnO:PEI (93:7, w/w) as the ETL, the power conversion efficiency (PCE) of the P3HT:PC61BM (1:1, w/w) device improved to 4.6% from a value of 3.7% for the corresponding device that incorporated pristine ZnO as the ETL-a relative increase of 24%. For the PBDTTBO:PC71BM (1:2, w/w) device featuring the same amount of PEI blended in the ETL, the PCE improved to 8.7% from a value of 7.3% for the corresponding device that featured pure ZnO as its ETL-a relative increase of 20%. Accordingly, ZnO:PEI composites can be effective ETLs within organic photovoltaics.
URI: http://dx.doi.org/10.1021/acsami.5b00521
ISSN: 1944-8244
DOI: 10.1021/acsami.5b00521
Issue: 11
Begin Page: 6273
End Page: 6281
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