Systematic investigation of organic photovoltaic cell charge injection/performance modulation by dipolar organosilane interfacial layers.
With the goal of investigating and enhancing anode performance in bulk-heterojunction (BHJ) organic photovoltaic (OPV) cells, the glass/tin-doped indium oxide (ITO) anodes are modified with a series of robust silane-tethered bis(fluoroaryl)amines to form self-assembled interfacial layers (IFLs). The modified ITO anodes are characterized by contact angle measurements, X-ray reflectivity, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, atomic force microscopy, and cyclic voltammetry. These techniques reveal the presence of hydrophobic amorphous monolayers of 6.68 to 9.76 Å thickness, and modified anode work functions ranging from 4.66 to 5.27 eV. Two series of glass/ITO/IFL/active layer/LiF/Al BHJ OPVs are fabricated with the active layer = poly(3-hexylthiophene):phenyl-C71-butyric acid methyl ester (P3HT:PC71BM) or poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)-carbonyl]thi-eno[3,4-b]thiophenediyl]]:phenyl-C71-butyric acid methyl ester (PTB7:PC71BM). OPV analysis under AM 1.5G conditions reveals significant performance enhancement versus unmodified glass/ITO anodes. Strong positive correlations between the electrochemically derived heterogeneous electron transport rate constants (ks) and the device open circuit voltage (Voc), short circuit current (Jsc), hence OPV power conversion efficiency (PCE), are observed for these modified anodes. Furthermore, the strong functional dependence of the device response on ks increases as greater densities of charge carriers are generated in the BHJ OPV active layer, and is attributable to enhanced anode carrier extraction in the case of high-ks IFLs.
Department of Chemistry and the Argonne-Northwestern Solar Energy Research Center, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Charles Kiseok
CK
Song
Alicia C
AC
White
Li
L
Zeng
Benjamin J
BJ
Leever
Michael D
MD
Clark
Jonathan D
JD
Emery
Sylvia J
SJ
Lou
Amod
A
Timalsina
Lin X
LX
Chen
Michael J
MJ
Bedzyk
Tobin J
TJ
Marks
D000588:Amines / Q000737:chemistry; D004566:Electrodes; D037741:Fullerenes / Q000737:chemistry; D005898:Glass / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D012821:Silanes / Q000737:chemistry; D012993:Solar Energy; D013876:Thiophenes / Q000737:chemistry; D017971:Tin Compounds / Q000737:chemistry
D000588:Amines; D037741:Fullerenes; D012821:Silanes; D013876:Thiophenes; D017971:Tin Compounds; C507295:poly(3-hexylthiophene); C109984:indium tin oxide