High-Quality Additive-Free -FAPbI₃ Film Fabricated by Alkane/Nanocrystals Method and Surface Chemistry Modulation for Efficient Perovskite Solar Cell

It's still a scientific issue to synthesize exotic amines-free and pure-phase FAPbI(3) film because most FAPbI(3) films are synthesized by adding MACl-like exotic amines salts in their precursor solution to reduce the phase transition barrier. In this work, high-quality and additive-free phase-pure alpha-FAPbI(3) films are successfully fabricated via the sustainable Alkane/Nanocrystals method. FAPbI(3) nanocrystals (NCs) are performed as the heterogeneous nuclei to promote the nucleation and crystallization of FAPbI(3) films. Cryogenic-TEM and in situ GIWAXS evidence the seed function and interesting phase evolution of FAPbI(3) NCs. The whole phase transition course of pure FAPbI(3) film is systematically studied. IR-AFM and ToF-SIMS reveal ligands capped on NCs are extruded to the film surface. PbAc-IPA solution treating the film surface can effectively wash off the surplus ligands at the surface and modulate the surface chemistry and energy levels. As a result, an average power conversion efficiency (PCE) of 21.45% is achieved for MA-free pure alpha-FAPbI(3) perovskite solar cells (PSCs), as well as the best light-soaking stability record of retaining 95% of the initial PCE after 800 h. This work paves a new way to fabricate MA-free pure alpha-FAPbI(3) PSCs.