Evidence of Nitrogen Contribution to the Electronic Structure of the CH₃NH₃PbI₃ Perovskite

Abstract

Despite fast development of hybrid perovskite solar cells, there are many fundamental questions related to the perovskite film which remain open. For example, there are contradicting theoretical reports on the role of the organic methylammonium cation (CH NH ) in the methylammonium lead triiodide (CH NH PbI ) perovskite film. From one side it is reported that the organic cation does not contribute to electronic structure of the CH NH PbI film. From the other side, valence band maximum fluctuations, dependent on the CH NH rotation, have been theoretically predicted. The resonant X-ray photoelectron spectroscopy results reported here show experimental evidence of nitrogen contribution to the CH NH PbI electronic structure. Moreover, the observed strong resonances of nitrogen with the I 5s and the Pb 5d-6s levels indicate that the CH NH PbI valence band is extended up to ≈18 eV below the Fermi energy, and therefore one should also consider these shallow core levels while modeling its electronic structure.

Room‐Temperature Atomic‐Layer‐Deposited Al2O3 Improves the Efficiency of Perovskite Solar Cells over Time

“…The O1ss pectrum ( Figure 3e)c an be fitted with two peaks at 532.0 and 533.3 eV.T he former can be attributed to PbOH, and the latter to CH 3 OH. Figure S2 shows that, during the initial ALD process, the PbOH peak (138.2 eV) in the Pb 4f region disappears and an ew peak with much lower intensity rises at about 137 eV.T his new peak can be attributedt oP b metal [12] owing to reduction of PbOH to Pb by TMA. In the valence-band spectrum of the perovskite film ( Figure 3g)O2s, Pb 5d, I5s, Pb 6s, O2pa nd I6pc omponents can be distinguished.…”

“…Therefore, formation of PbÀOH bonds can be excluded, and the peak at 532.0 eV can be assigned to the formationo fc hemical bonds between Al and Oo rO H. The valence-band signal after the RT-ALD process is dominated by emissions from the O2sa nd O2pl evels,a nd thus confirms formation of an ALD overlayer on top of the perovskite film. Figure S2 shows that, during the initial ALD process, the PbOH peak (138.2 eV) in the Pb 4f region disappears and an ew peak with much lower intensity rises at about 137 eV.T his new peak can be attributedt oP b metal [12] owing to reduction of PbOH to Pb by TMA. Also, initial reduction of CH 3 OH (285.7 eV)a nd OÀCÀH( 289.7 eV) groups by TMA is observed in the C1ss pectra ( Figure S2).…”

“…In the valence-band spectrum of the perovskite film ( Figure 3g)O2s, Pb 5d, I5s, Pb 6s, O2pa nd I6pc omponents can be distinguished. [12] After 50 RT-ALD cycles of TMA and H 2 Oo nC H 3 NH 3 PbI 3 (Figure 3a-g), all peaks relatedt ot he perovskite film are attenuated and those related to the ALD process (Al 2p, O1s, O2sa nd O2p) are more intense. In the Al 2p core-level spectrum (Figure 3f According to theNIST database, [11] the first pair can be attributed to AlOOH, Al(OH) 3 ,A l(ox) (ox = oxide), or Al 2 O 3 ,a nd the second pair to CH 3 OH.…”

“…[11] The N1ss pectrum ( Figure 3b)c an be deconvoluted into two peaks at 400.6 and 402.6 eV,w hichc an be attributedt oC H 3 CN or NH 3 and CH 3 NH 3 ,r espectively. [12] After 50 RT-ALD cycles of TMA and H 2 Oo nC H 3 NH 3 PbI 3 (Figure 3a-g), all peaks relatedt ot he perovskite film are attenuated and those related to the ALD process (Al 2p, O1s, O2sa nd O2p) are more intense. [11] The I3ds pectrum ( Figure 3d)c an be fitted with an I3d 5/2 component at 619.6 eV and can be attributed to CH 3 I.…”

Electron spectroscopy of ionic liquids: experimental identification of atomic orbital contributions to valence electronic structure

“…RAES has been used to study the valence electronic structure of the condensed phase for: ionic crystals (e.g. CaF2, 40 BN 41 Na[NO3] 42,43 ), a range of small organic molecules (nitrogen heterocycles, 44 furan and pyrrole, 45,46 ethylene and cyclohexane, 47 benzene, 48 acrylonitrile 49 ), a thiophene oligomer, 50 polymers [51][52][53] , proteins, 54 DNA, 55,56 water, 57 perovskite, 58 and ions in aqueous solution [59][60][61][62][63] , but not for ILs to the best of our knowledge.…”