Abstract
An innovative bilayer cathode interlayer (CIL) with a nanostructure consisting of in situ thermal reduced graphene oxide (ITR-GO) and poly[(9,9-bis(3′-(N,N-dimethylamion)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl) fluorene] (PFN) has been fabricated for inverted organic solar cells (OSCs). An approach to prepare a CIL of high electronic quality by using ITR-GO as a template to modulate the morphology of the interface between the active layer and electrode and to further reduce the work function of the electrode has also been realized. This bilayer ITR-GO/PFN CIL is processed by a spray-coating method with facile in situ thermal reduction. Meanwhile, the CIL shows a good charge transport efficiency and less charge recombination, which leads to a significant enhancement of the power conversion efficiency from 6.47% to 8.34% for Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl} (PTB7):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)-based OSCs. In addition, the long-term stability of the OSC is improved by using the ITR-GO/PFN CIL when compared with the pristine device. These results indicate that the bilayer ITR-GO/PFN CIL is a promising way to realize high-efficiency and stable OSCs by using water-soluble conjugated polymer electrolytes such as PFN.
Highlights
Bulk heterojunction (BHJ) organic solar cells (OSCs) have drawn many interests in the past decades because of their suitability in the industrial manufacturing of large-area and flexible devices and in low-cost processing [1,2,3,4,5]
It has been demonstrated that interfacial engineering, such as inserting functional cathode interfacial layers (CILs) between the indium tin oxide (ITO) electrode and BHJ layer, plays a significant role in improving charge transportation and collection efficiency for inverted OSCs [10,11]
A large number of materials have been utilized as the CILs in OSCs, such as n-type metaloxides (zinc oxide (ZnO), titaniumoxide (TiOx), aluminum oxide (Al2O3), etc.) [12,13,14,15], metallic compounds (ZnS, CdS, etc.) [16,17], and conjugated polymer electrolytes (CPEs; poly[(9,9-bis(3 -(N,N-dimethylamino)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), etc.) [18,19,20]
Summary
Bulk heterojunction (BHJ) organic solar cells (OSCs) have drawn many interests in the past decades because of their suitability in the industrial manufacturing of large-area and flexible devices and in low-cost processing [1,2,3,4,5]. PFN spray-coated on single-layer ITR-GO (S-ITR-GO) can result in better energy-level alignment and a smoothed surface, enhancing charge-extraction efficiency and reducing recombination losses for the OSCs. As a result, by using the S-ITR-GO/PFN bilayer CIL, a significant enhancement in the PCE from 6.47% to 8.34% for a PTB7:PC71BM system has been obtained. The long-term stability of the OSC by using the ITR-GO/PFN CIL is improved, when compared with the pristine device
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