Direct tuning of the band gap via electronically-active organic cations and large piezoelectric response in one-dimensional hybrid halides from first-principles

By inserting C₇H₇⁺ cations into 1D GAPbI₃, the band gap is directly narrowed from 2.28 to 0.69 eV. In addition, a large piezoelectric response is also predicted in 1D GAPbI₃.