Reduced Band Gap Hybrid Perovskites Resulting from Combined Hydrogen and Halogen Bonding at the Organic−Inorganic Interface

Undistorted perovskite layers are formed in PbI 4 -based hybrid perovskites incorporating X−(CH 2 ) 2 −NH 3 + (X = Br, Cl) cations. The outstanding structural feature of these compounds is the result of halogen and hydrogen bonding at the organic−inorganic interface, leading to the absence of hydrogen bonds between equatorial iodine atoms of the perovskite layer and ammonium parts, these last being located out of perovskite layers. As a consequence, these red salts display a reduced band gap (2.2 eV) which is assigned to a more disperse HOMO band compared to other salts such as (I−(CH 2 ) 2 −NH 3 ) 2 PbI 4 .