a) Absorption spectra at T = 300 and 10 K for 1) C10–PbI4, 2) PhE–PbI4, and 3) PhE–Pb2I7. Reproduced with permission.[qv: 77b] Copyright 1992, American Physical Society. b) Femtosecond vibrational spectroscopy and PL dependence on temperature. Reproduced with permission.95 Copyright 2017, American Chemical Society. c) UV–vis absorption spectra for 2D hybrid organic–inorganic perovskite films. Reproduced with permission.26 Copyright 2017, American Chemical Society. d) Tauc plots of (PEA)2Ge1−
xSnxI4 (x = 0, 0.125, 0.25, 0.5). Photographs of the compounds with different Sn content are shown as inset. Reproduced with permission.102 Copyright 2018, American Chemical Society. e,f) Optical absorbance spectra of PhE–PbI4(1−
x
)Br4
x and PhE–PbBr4(1−
x
)Cl4
x. Reproduced with permission.[qv: 103] Copyright 2014, American Chemical Society. g) Electronic band structure of the polar configurations of selected (BA)2(MA)n
−1PbnI3
n
+1 perovskites. Reproduced with permission.[qv: 25a] Copyright 2016, American Chemical Society. h) Absorption of the exfoliated crystals. Reproduced with permission.80 Copyright 2017, AAAS.