Solution deposition struggles to achieve conformal and pinhole-free wide-bandgap (WBG) perovskite films on micrometer-scale textured silicon subcells due to challenges in nucleation dynamics and film uniformity, necessitating smaller textures in the efficient perovskite/silicon tandems, which compromise light trapping and current density. While evaporation-assisted two-step deposition improves conformality, it often yields films with suboptimal crystallinity and a high defect density. To address this, we elucidate the formation mechanism of CsPbIxBr3-x nanocrystals during the thermal evaporation of PbI2/CsBr templates, which can serve as preferential nucleation sites to facilitate the growth of high-quality perovskite films. By optimizing evaporation conditions and incorporating 2,3,4,5,6-pentafluorobenzylphosphonic acid (pFBPA) during the spin-coating process, we achieved enhanced crystallization kinetics of nucleation sites and improved perovskite film uniformity. Further interface modification with pFBPA and ethane-1,2-diammonium iodide induces targeted surface dipoles at both carrier transport layers/perovskite interfaces, which not only offers better band alignment and surface passivation at both interfaces but also creates an enhanced electric field to boost electron extraction. These advancements enabled a WBG (1.68 eV) perovskite solar cell (PSC) to achieve an impressive power conversion efficiency (PCE) among WBG (1.65-1.7 eV) PSCs based on evaporation-assisted deposition. This study provides fundamental insights into achieving conformal high-quality WBG perovskite films, offering a theoretical foundation for the development of efficient perovskite/silicon tandems.
Keywords: crystallization kinetics; evaporation-assisted two-step deposition; interface modification; nucleation sites; surface dipole; wide-bandgap perovskite solar cells.
