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 BiI63- containing compound with a series of more common iodobismuthates, especially the dinuclear Bi2I93- 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%.