Formation of High‐Performance Multi‐Cation Halide Perovskites Photovoltaics by δ‐CsPbI<sub>3</sub>/δ‐RbPbI<sub>3</sub> Seed‐Assisted Heterogeneous Nucleation
Essa A. Alharbi, Thomas Baumeler, Anurag Krishna, A. Alyamani, Felix T. Eickemeyer, Olivier Ouellette, Linfeng Pan, Fahad S. Alghamdi, Zaiwei Wang, Mohammad Hayal Alotaibi, Bowen Yang, Masaud Almalki, Mounir Mensi, Hamad Albrithen, Abdulrahman Albadri, Anders Hagfeldt, Shaik M. Zakeeruddin, Michaël Grätzel
Abstract
Abstract The performance of perovskite solar cells is highly dependent on the fabrication method; thus, controlling the growth mechanism of perovskite crystals is a promising way towards increasing their efficiency and stability. Herein, a multi‐cation halide composition of perovskite solar cells is engineered via the two‐step sequential deposition method. Strikingly, it is found that adding mixtures of 1D polymorphs of orthorhombic δ‐RbPbI 3 and δ‐CsPbI 3 to the PbI 2 precursor solution induces the formation of porous mesostructured hexagonal films. This porosity greatly facilitates the heterogeneous nucleation and the penetration of FA (formamidinium)/MA (methylammonium) cations within the PbI 2 film. Thus, the subsequent conversion of PbI 2 into the desired multication cubic α‐structure by exposing it to a solution of formamidinium methylammonium halides is greatly enhanced. During the conversion step, the δ‐CsPbI 3 also is fully integrated into the 3D mixed cation perovskite lattice, which exhibits high crystallinity and superior optoelectronic properties. The champion device shows a power conversion efficiency (PCE) over 22%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining more than 90% of its initial value of PCE under 1 Sun illumination with maximum power point tracking for 400 h.