Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 13, Issue 10, Pages 12296-12304Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.1c00350
Keywords
cross-linkable polymer; cathode interface layer; organic solar cells; photovoltaic efficiency; environmental stability
Funding
- National Natural Science Foundation of China [51703040, 52063010, 51961010, 51521002]
- Natural Science Foundation of Guangxi Province [2017GXNSFAA198174]
- Applied Basic Research Major Program of Guangdong Province [2019B030302007]
- Young Innovative Talent Project for Higher Education Institution of Guangdong Province [2018KQNCX239]
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A novel cross-linkable and alcohol-soluble pyridine-incorporated polyfluorene derivative, PFOPy, was synthesized and used as a cathode interface layer in organic solar cells (OSCs), exhibiting excellent solvent resistance, reduced work function, and improved interface contact, leading to significant improvements in photovoltaic performance and stability.
Device performance and commercialization of organic solar cells (OSCs) are strongly influenced by the characteristics of the interface layers. Cross-linked polymer interface layers with solvent-resistant properties are very compatible with large-area solution-processing methods of OSCs and may be beneficial to the environmental stability of OSCs due to the viscoelastic and cross-linked characteristics of the crosslinked polymer. In this work, a novel cross-linkable and alcohol-soluble pyridine-incorporated polyfluorene derivative, denoted as PFOPy, is synthesized and used as a cathode interface layer (CIL) in OSCs. For PFOPy, the pendant epoxy group can be effectively cross linked through cationic polymerization under thermal treatment and the pendant pyridine group can offer good alcohol solubility. Optical absorption tests of PFOPy films before/after washing by chloroform demonstrate the excellent solvent-resistance property for the cross-linked PFOPy film. Compared with the typical ZnO CIL, the cross-linked PFOPy CIL can also substantially reduce ITO's work function and form a better interface contact with the active layer. Utilizing an inverted device structure and a typical active layer of PM6:Y6, ZnO-based OSCs display an optimal power conversion efficiency (PCE) of 15.83% while PFOPybased OSCs exhibit superior photovoltaic performance with an optimal PCE of 16.20%. Moreover, ZnO-based and PFOPy-based OSCs separately maintain 89% and 90% of the corresponding initial PCE after 12 h of illumination, indicating similarly excellent photostability. More importantly, after 26 complete thermal cycles, ZnO-based OSCs only maintain 81% of the initial PCE while PFOPy-based OSCs retain 92% of the initial PCE and exhibit obviously better thermal cycling stability, indicating that the cross-linked PFOPy CIL should offer stronger interface robustness against thermal cycling stress due to the viscoelastic and cross-linked characteristics of PFOPy. The impressive results indicate that the cross-linked PFOPy CIL would be a very promising CIL in OSCs.
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