Deciphering perovskite crystal growth in interdiffusion protocol for planar heterojunction photovoltaic devices

Hybrid organic-inorganic perovskites (HIOPs) have increasingly promoted the photovoltaic field due to their excellent semiconductor properties and inexpensive costs. Interdiffusion protocol has been regarded as an efficient approach to deposit high-quality HIOP films. Nevertheless, the underlying mechanism of this protocol remains obscured. In this work, in virtue of vapor-deposited lead halide frame to eliminate solution-driven lead halide effect, we thoroughly studied the evolution of different HIOP films by symmetrically controlling the initial lead halides as well as organic salts. The crystal growth mechanism of the interdiffusion can be drawn in two aspects: 1. CH3NH3 (MA)-HIOP shows higher nucleation rate than (NH2)(2)CH (FA)-HIOP; 2. FA-HIOP and PbCl2HIOP exhibit greater coarsening rates than other colleagues. Most importantly, conflicting lattice with Cl-barren phase and Cl-rich phase is first uncovered for MA-HIOP and FA-HIOP using PbCl2 frame. All the device performances based on these films also prove the potential mechanism, and champion efficiency of 16.01% is achieved based on FAPbI(3). This work will provide in-depth insight into the interdiffusion protocol and drive this protocol toward multiple photovoltaic applications by facilely controlling precursor compositions.