Single-walled carbon nanotubes (CNTs)
has been considered as a
promising material for a top electrode of perovskite solar cells owing
to its hydrophobic nature, earth-abundance, and mechanical robustness.
However, its poor conductivity, a shallow work function, and nonreflective
nature have limited further enhancement in power conversion efficiency
(PCE) of top CNT electrode-based perovskite solar cells. Here, we
introduced a simple and scalable method to address these issues by
utilizing an ex-situ vapor-assisted doping method. Trifluoromethanesulfonic
acid (TFMS) vapor doping of the free-standing CNT sheet enabled tuning
of conductivity and work function of the CNT electrode without damaging
underneath layers. The sheet resistance of the CNT sheet was decreased
by 21.3% with an increase in work function from 4.75 to 4.96 eV upon
doping of TFMS. In addition, recently developed 2D perovskite-protected
Cs-containing formamidium lead iodide (FACsPbI3) technology
was employed to maximize the absorption. Because of the lowered resistance,
better energy alignment, and improved absorption, the CNT electrode-based
PSCs produced a PCE of 17.6% with a J
SC of 24.21 mA/cm2, V
OC of 1.005
V, and FF of 0.72. Furthermore, the resulting TFMS-doped CNT-PSCs
demonstrated higher thermal and operational stability than bare CNT
and metal electrode-based devices.
A novel, hyperbranched, amphiphilic multiarm biodegradable polyethylenimine-poly(gamma-benzyl-L-glutamate) (PEI-PBLG) copolymer was prepared by the ring-opening polymerization of gamma-benzyl-L-glutamate-N-carboxyanhydride (BLG-NCA) with hyperbranched PEI as a macroinitiator. The copolymer could self-assemble into core-shell micelles in aqueous solution with highly hydrophobic micelle cores. As the PBLG content was increased, the size of the micelles increased and the critical micelle concentration (CMC) decreased. The surface of the micelles had a positive zeta potential. The cationic micelles were capable of complexing with plasmid DNA (pDNA), which could be released subsequently by treatment with polyanions. The PEI-PBLG copolymer formed unimolecular micelles in chloroform solution. The pH-sensitive phase-transfer behavior exhibited two critical pH points for triggering the encapsulation and release of guest molecules. Both the encapsulation and release processes were rapid and reversible. Under strong acidic or alkaline conditions, the release process became partially or completely irreversible. Thus, this copolymer system should be an attractive candidate for a gene- or drug-delivery system in aqueous media and could provide the phase-transfer carriers between water and organic media.
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