Zero-dimensional hybrid iodobismuthate derivatives: from structure study to photovoltaic application

The quest for lead-free light-absorbing perovskite materials has long been the target of researchers to make the 'star' material friendly to the commercial market. After a summary of different lead-free solar absorbers, we demonstrate a zero-dimensional iodobismuthate (MA)₃[BiI₆]·3MACl (MA: CH₃NH₃) featuring isolated hexaiodobismuthate(iii) anions in the crystal analysis. The unexpectedly formed material was made via an orthogonal solvent permeation method and the decomposition of the guest solvent. We compare the BiI₆^3- containing compound with a series of more common iodobismuthates, especially the dinuclear Bi₂I₉^3- in terms of dimensionalities via single-crystal diffraction and DFT calculations, respectively. An undocumented second-order phase transition was found between 190 K and 160 K for the dimeric MA₃Bi₂I₉. The photovoltaic device from a thermally reorganized polycrystalline film of (MA)₃[BiI₆]·3MACl, which resembled the structure of (MA)₃[Bi₂I₉] gave a power conversion efficiency of 1.09%.