Green-Solvent Engineering for Depositing Qualified Phenyl-C61-butyl Acid Methyl Ester Films for Inverted Flexible Perovskite Solar Cells

Abstract

Flexible perovskite solar cells (fPSCs) with the inverted structure (p-i-n structure) show a promising commercialization future, owing to their lightweight and high efficiencies. Phenyl-C61-butyric-acid methyl ester (PCBM) is widely used as the n-type material due to its excellent conductivity and solvent processability. However, the commonly used chlorobenzene (CB), as the solvent of PCBM solution, is well recognized as a halogenated contaminant in the environment and is harmful to human health. There is an imperative need to develop nonhalogenated green solvents to replace CB. This work discusses the selection of green solvents based on the Hansen solubility parameters (HSPs). It is found that 2-methylanisole (2-MEA) acts as an excellent alternative to CB, with which high-quality PCBM films could be deposited. The experimental and theoretical studies demonstrate that 2-MEA can suppress the formation of PCBM aggregations during the solvation process compared with CB. The more uniform PCBM film achieved from the 2-MEA solution benefits carrier extraction at the electronic transport layer (ETL)/ perovskite interface. As a result, better efficiencies are received among fPSCs based on the 2-MEA-processed PCBM, superior to that of the fPSCs based on the CB-processed PCBM. Moreover, using 1,8-diiodooctane (DIO) as a solvent additive is proven to further increase the solubility of PCBM in the 2-MEA solution, resulting in enhanced efficiencies of the flexible PSCs by more than 5% (from 19.25 to 20.30%). The developed green-solvent strategy is of great importance for the future large-scale production of environmentally sustainable fPSCs.

Phase-Engineering of Layered Nickel Hydroxide for Synthesizing High-Quality NiOx Nanocrystals for Efficient Inverted Flexible Perovskite Solar Cells

“…NiO x powders were synthesized according to previous reports. ,, Typically, Ni­(NO 3 ) 2 ·6H 2 O (21.81 g) was dissolved in deionized water (15 mL). Then, a certain amount of NaOH, KOH, LiOH·H 2 O, or TEAOH was dissolved in deionized water and added drop by drop to Ni­(NO 3 ) 2 ·6H 2 O solution with vigorous stirring.…”

“…PbI 2 , MABr, CsI, FAI, and MAI were dissolved in a mixed solvent of DMF/DMSO (4:1 V/V) to prepare 1.4 M Cs 0.05 (FA 0.92 MA 0.08 ) 0.95 Pb­(I 0.92 Br 0.08 ) 3 precursor solution. , To further improve the fPSCs’ performance, 0.1 mol % capsaicin and 0.3 mol % BMIMBF 4 (to Pb) were added to the perovskite precursor solution. , The perovskite solution was spin-coated on the as-prepared NiO x film at 1500 rpm for 10 s, followed by 6000 rpm for 25 s. Anisole (200 μL) was quickly dropped onto the spinning substrates 5 s before the end of the program. The perovskite film was immediately transferred onto the hotplate and heated at 100 °C for 30 min.…”

“…Among them, the coating methods based on NiO x -nanocrystal inks have become a widely used technology for the preparation of flexible devices because of their low cost, high performance, and lowtemperature processing (<150 °C). 28,30 Generally, NiO x nanocrystals were prepared via calcinating layered Ni(OH) 2 originating from a salt-alkali precipitation reaction. However, previous reports indicated that the anions and cations in the reacting solution are easily trapped in the layered Ni(OH) 2 during precipitation.…”

“…One is organic functional materials, such as poly [bis (4-phenyl) (2,4,6-trimethylphenyl)-amine] (PTAA), poly­(3,4-ethylene dioxythiophene)–polystyrene sulfonate (PEDOT: PSS), polythiophene, and so on. ,− Although these organic functional materials have been successfully applied, they suffer from long-term stability, high cost, and batch-to-batch reproducibility. The second one is inorganic semiconductor materials, such as NiO x , CuSCN, Cu 2 O, etc. − Among them, NiO x is an essential material with excellent characteristics, including low cost, diverse preparation methods, and excellent thermal stability. ,,− More importantly, it has an ideal energetic alignment with perovskite materials. Thus it has become a famous star in the field of inverted PSCs in recent years.…”

“…NiO x films can be deposited by magnetron sputtering, ,, thermal vapor deposition, , spray pyrolysis, , pulsed laser deposition, sol–gel deposition and pyrolysis, , coating with NiO x -nanocrystal inks, and so on. Among them, the coating methods based on NiO x -nanocrystal inks have become a widely used technology for the preparation of flexible devices because of their low cost, high performance, and low-temperature processing (<150 °C). , Generally, NiO x nanocrystals were prepared via calcinating layered Ni­(OH) 2 originating from a salt-alkali precipitation reaction. However, previous reports indicated that the anions and cations in the reacting solution are easily trapped in the layered Ni­(OH) 2 during precipitation. − The ion impurities cannot be thoroughly removed by subsequent washing and calcination at 275 °C, impairing the PSCs’ efficiency and long-term stability.…”