Spiro ometad

The planar PSC device structure was fabricated using an ITO glass substrate as a bottom electrode, a c-TiO₂ layer as an ETL by spray pyrolysis as described previously, a light-absorbing perovskite layer (MAPbI₃), 2,2′,7,7′-tetrakis{N,N-di(4-methoxyphenyl)amino}-9,9′-spirobifluorene (Spiro-OMeTAD, Merck) as an HTL, and a top Au electrode deposited by thermal evaporation. After the c-TiO₂ layer on the ITO substrate was cooled to room temperature, a one-step method developed by Ahn N. et al.,^{17 (link)} was used with 422 mg of PbI₂, 159 mg of MAI, and 78 mg of DMSO (molar ratio 1 : 1 : 1) as perovskite precursor. Then, raw materials were mixed in 600 mg of DMF solution and stirred for one hour at room temperature. The perovskite was spin-coated onto the compact TiO₂ layer at 5000 rpm for 30 s with 300 μl of diethyl ether as an antisolvent solution. Then the samples were annealed at 100 °C for 30 min. Next, the Spiro-OMeTAD solution was prepared by using 80 mg Spiro-OMeTAD, 22.5 ml 4-tertbutylpyridine (Sigma-Aldrich) and 17.5 ml lithium bis(trifluoromethane sulfonyl)imide (Li-TFSI, Sigma-Aldrich) solution (520 mg Li-TFSI in 1 ml acetonitrile) in 1 ml chlorobenzene, and then spin-coating the resulting solution onto the perovskite layer at 3000 rpm for 30 s. Finally, Au was deposited on this HTL by thermal vacuum evaporation as a top electrode.

After the perovskite annealing, the substrates were cooled down for a few minutes, and a spiro-OMeTAD (Merck) solution (70 mM in chlorobenzene) was spin-coated at 4,000 rpm for 20 s. spiro-OMeTAD was doped with bis(trifluoromethylsulfonyl)imide lithium salt (Li-TFSI) (Sigma-Aldrich), tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)-cobalt(III) tris(bis(trifluoromethylsulfonyl)imide) (FK209) (Dynamo), and 4-tert-butylpyridine (tBP) (Sigma-Aldrich). The molar ratios of additives for spiro-OMeTAD were 0.5, 0.03, and 3.3 for Li-TFSI, FK209, and tBP, respectively. Finally, 80 nm of gold top electrode were thermally evaporated under high vacuum.
Perovskite solar cells were then stabilized with a photopolymerized coating accordingly to previously reported procedure (26 (link)).