Epitaxial Growth of α‐FAPbI3 at a Well‐Matched Heterointerface for Efficient Perovskite Solar Cells and Solar Modules

Although the FAPbI3 perovskite system exhibits an impressive optoelectronic characteristic and thermal stability because of its energetically unstable black phase at room temperature, it is considerably challenging to attain a controllable and oriented nucleation of α‐FAPbI3. To overcome this challenge, a 2D perovskite with a released inorganic octahedral distortion designed by weakening the hydrogen interactions between the organic interlayer and [PbI6]4− octahedron is presented in this study. A highly matched heterointerface can be formed between the (002) facet of the 2D structure and the (100) crystal plane of the cubic α‐FAPbI3, thereby lowering the crystallization energy and inducing a heterogeneous nucleation of α‐FAPbI3. This “epitaxial growth” mechanism results form the highly preferred crystallographic orientation of the (100) facets, improved crystal quality and film uniformity, substantially increased charge transporting characteristics, and suppressed nonradiative recombination losses. An impressive power conversion efficiency (PCE) of 25.4% (certified 25.2%) is achieved using target PSCs, which demonstrates outstanding ambient and operational stability. The feasibility of this strategy is proved for the scalable deposition of homogeneous and high‐quality perovskite thin films by demonstrating the remarkably increased PCE of the large‐area perovskite solar module, from 18.2% to 20.1%. A released distortion of 2D perovskite ((NAM)2PbI4) with large Pb‐I‐Pb angle is realized via weakening the hydrogen bonding between organic spacer and [PbI6]4− octahedron. It leads to the formation of well‐matched heterointerface between (002) facet of (NAM)2PbI4 and (100) plane of FAPbI3, which lowers the crystal formation energy and triggers the epitaxial growth α‐FAPbI3. An impressive power conversion efficiency of 25.4% (certified 25.2%) is achieved by the target perovskite solar cells, along with enhanced stability.