Stability of Polymer Interlayer Modified ITO Electrodes for Organic Solar Cells

Abstract

Indium-tin-oxide (ITO) electrode surfaces were modified using thin polymeric films of ethoxylated polyethylenimine (PEIE) and poly(3,3′-([(9′,9′-dioctyl-9H,9′H-[2,2′-bifluorene]-9,9-diyl)bis(4,1-phenylene)]bis(oxy))bis(N,N-dimethylpropan-1-amine)) (PFPA-1) to investigate the resultant work function and its stability in ambient atmosphere. Both PEIE and PFPA-1 were found to significantly reduce the ITO work function, as a result of a surface dipole at the ITO–polymer interface. After aging for two weeks in ambient air atmosphere, the N-side groups and OH groups in PEIE-modified ITO were found to realign themselves away from the polymer surface, resulting in an orientation more parallel to the surface normal and thus in an increase in work function from 3.5 to 3.8 eV. The work function of PFPA-1-modified ITO was found to increase from 3.65 to 4.1 eV after two weeks of aging in air due to a complete re-orientation of the polar side chains away from the surface, aligning the dipoles more parallel to the surface normal. In both PEIE and PFPA-1 samples, the hydrophobic aliphatic carbon was found to dominate the polymer surface, after aging.

Facile Synthesis of an Efficient and Robust Cathode Interface Material for Polymer Solar Cells

“…Figure shows the shift in the secondary electron cutoff of the ultraviolet photoelectron spectroscopy (UPS) spectra and schematically depicts the corresponding vacuum level shift at the ITO–PNDIT10N interface, as a result of surface modification. The observed reduction in the work function agrees well with literature values for amino-containing interface materials with tertiary amine or pyridine pendant groups. ,,,,, This notable work function reduction is related to the free electron pair on the nitrogen in the PNDIT10N side group forming an interfacial dipole . This interfacial dipole further facilitates the electron collection and transport from the BHJ layer to the ITO cathode …”

“…The observed reduction in the work function agrees well with literature values for amino-containing interface materials with tertiary amine or pyridine pendant groups. 12,17,29,48,57,58 This notable work function reduction is related to the free electron pair on the nitrogen in the PNDIT10N side group forming an interfacial dipole. 9 This interfacial dipole further facilitates the electron collection and transport from the BHJ layer to the ITO cathode.…”

“…PNDIT10N is processed from BnOH at ambient temperatures as a direct replacement for zinc oxide (ZnO), which is a commonly used inorganic CIL. As a comparison, ZnO is either processed from a zinc acetate solution, requiring high annealing temperatures, or deposited from nanoparticle ink. − The photovoltaic performance of PNDIT10N CIL is studied in inverted configuration for ITO/PNDIT10N/BHJ layer/molybdenum oxide (MoO x )/Ag systems. This is due to the better stability offered by inverted device configuration in comparison with conventional devices, providing an advantage for upscaling via roll-to-roll processing under ambient conditions .…”

Preparation of Surlyn films reinforced with cellulose nanofibres and feasibility of applying the transparent composite films for organic photovoltaic encapsulation

“…The performance and stability of these solar cells are known to be highly sensitive to moisture and oxygen. Sharma et al [ 1 ], for example, showed that the stability of the OPV cells was strongly affected by the moisture level. After ageing for two weeks in an ambient air atmosphere, the power conversion efficiency (PCE) of the cells dropped rapidly.…”

35th Australasian Polymer Symposium (APS) Research Highlights

“…include a report from plenary speaker Professor Mats Andersson on the 'Stability of Polymer Interlayer Modified ITO Electrodes for Organic Solar Cells'. [1] A highlight paper by invited keynote speaker Professor Christine Luscombe entitled 'Poly(3-hexylthiophene) End-Functionalization via Quenching Resulting in Heteroatom-Bond Formation' illustrates how changing the end-functional groups of P3HT to incorporate chalcogens opens up the opportunity to control and alter interactions with different materials. [2] Two review articles from early career researchers include Dr Katherine Locock's (CSIRO, Melbourne, Australia) review entitled 'Bioinspired Polymers: Antimicrobial Polymethacrylates' which traces the development of the antimicrobial polymethacrylates from the initial mimicry of global cationic and lipophilic AMP properties through to the level of specific amino acids present in the peptides.…”