Reduced band gap hybrid perovskites resulting from combined hydrogen and halogen bonding at the organic-inorganic interface

Undistorted perovskite layers are formed in PbI4-based hybrid perovskites incorporating X-(CH2)(2)-NH3+ (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-(CH2)(2)-NH3)(2)PbI4.