Improved Crystallization-Front Dynamics Reduce Buried-Interface Defects in Perovskite Solar Cells

Inverted perovskite solar cells have achieved substantial efficiency gains owing to advances in surface passivation; as a result, progress is now limited by buried defects at the perovskite/hole transport layer (HTL) interface. During top-down perovskite crystallization, the downward film-closure front eventually reaches precursor-phobic, low-surface-energy HTLs in a regime of severe local solution depletion, leading to interfacial solution cavities that then evolve into defects and voids, an issue that becomes increasingly pronounced with larger device areas. We hypothesize that pre-embedding adhesion-enhancing molecules at the HTL surface could trigger early buried-interface crystallization. This could produce solidification on a precursor-affine, homogeneous perovskite-terminated surface, preventing solution cavities and suppressing void formation. We explore a series of substrate-anchored crystallization accelerators, among which structures featuring isothiouronium templating groups we find to be the most impactful in promoting ionic assembly, strengthening substrate-precursor interactions, and accelerating crystallization at the buried interface, which allows final film coalescence to occur on a precrystallized perovskite surface. The strategy enables a void-suppressed buried interface with 8-fold lower defect density and a 1.5× increase in the yield of radiative recombination, enabling uniform performance across centimeter-scale areas. The resulting devices have certified quasi-steady-state power conversion efficiencies of 26.8% and 25.2% for 0.05 and 1.03 cm2 illuminated areas, respectively, and retain 80% of their initial efficiency after 1200 h of operation at 85 °C and 50% relative humidity.