Suppressing hydrogen bonds and controlling surface dipole: effective passivation for hydrophobic perovskite photoabsorber layers in solar cells

Abstract

Perovskite passivation is instrumental for state-of-the-art perovskite solar cells; however, the passivation effect has not been understood in detail. Herein, wettability measurements with selected solutions reveal that passivation is crucial...

An Architype-Cation-Based Room Temperature Ionic Liquid: Aliphatic-Primary-Ammonium Bis(Trifluoromethylsulfonyl)Imide as An Additive for Hole Transport Layers in Perovskite Solar Cells Allowing Spontaneous Passivation of The Perovskite Layer

“…The PSCs of were prepared along the conventional method with minor modifications. 10,11 (See SI for the details) Briefly, after deposition of titanium oxide (TiO2) ETM layer onto fluorine doped tin oxide (FTO) transparent conductive glass, FAPbI3 perovskite layer was deposited by spin-coating.…”

“…23 This spontaneous passivation will reduce the number of production process (i.e., the conventional passivation process will be skipped), which is advantageous in terms of industrialization. Besides, we have recently advocated that perovskite passivation with aliphatic ammoniums will reduce wettability of HTM solution over perovskite layer due to a decrease in surface tension of the dipole term, 11 which would be detrimental for large scale PV module fabrication, whereas this spontaneous passivation proposed in this work will address this issue. In order to realize this spontaneous passivation, alkyl-primaryammoniums will be prominent candidate for the RTIL cation because of its prominent reactivity to perovskites and its thin morphology for dense perovskite passivation, compared to the counter cations in the modern RTILs.…”

“…While efficient correction of both electrons and holes is vital for high performance PSCs, the carrier mobility of organic HTM (e.g., Spiro-OMeTAD) generally is less than that of inorganic ETM (e.g., TiO2), and control of HTM/perovskite interface significantly affects PSC performance involving its stability. [8][9][10][11] Thus, an application of RTIL to facilitate the hole collection in PSCs will be a promising target.…”

“…To control the HTM/perovskite interface, one of the recent progresses is introduction of passivation layer over perovskite. [8][9][10][11] For the passivator material, solid salts based on primary-ammonium that has accessible cationic moiety (e.g., n-octyl-ammonium iodide (OAI)), has been primely used, 8,10 especially combining with formamidinium-based perovskite (FAPbI3) that possess the bandgap relatively close to the ideal value (~1.4 eV) for single junction solar cells. 10 This passivation is effective to improve open circuit voltage (Voc) owing to the mitigation of carrier recombination in the HTM/perovskite interface and to render perovskite surface hydrophobic, which plays important role for the stability against humidity.…”

“…10 This passivation is effective to improve open circuit voltage (Voc) owing to the mitigation of carrier recombination in the HTM/perovskite interface and to render perovskite surface hydrophobic, which plays important role for the stability against humidity. [8][9][10][11] Hence, the passivation has become vital for the state-of-the art PSCs, resulting in requirement of the extra process (i.e., passivation post treatment) after deposition of perovskite layer though. As for HTM layer composition, organic semiconductors whose conductivity are improved by additives consisting of TFSI anions (e.g., lithium (Li)-TFSI: the most common additive) have been generally employed in PSCs.…”