Ionic liquids tailoring crystal orientation and electronic properties for stable perovskite solar cells.

The crystallization behavior of perovskite films has a profound influence on the resulting defect densities, charge carrier dynamics and photovoltaic performance. Herein, we introduce ionic liquids into the perovskite component to tailor the crystal growth of perovskite films from a disordered to a preferential corner-up orientation and accordingly increase the charge carrier mobility to accelerate electron transport and extraction. Using time-resolved measurements, we probe the charge carrier generation, transport and recombination behavior in these films and related devices. We find the ionic liquid-containing samples exhibit lower defects, faster charge carrier transport and suppressed non-radiative recombination, contributing to higher efficiency and fill factor. Via operando grazing-incidence small- and wide-angle X-ray scattering measurements, we observe a light-induced lattice compression and grain fragmentation in the control devices, whereas the ionic liquid-containing devices exhibit a slight light-induced crystal reconstitution and stronger tolerance against illumination. Under ambient conditions, the non-encapsulated device with the pyrrolidinium-based ionic compound (Pyr 14 BF 4) maintains 97% of its initial efficiency after 4368 h. [Display omitted] • Perovskite crystal growth is tailored by ionic liquid addition. • Ionic liquid addition suppressed non-radiative recombination. • Operando studies reveal insights in light-induced lattice compression and grain fragmentation. • Performance is improved with ionic liquid addition. • Stability is improved with ionic liquid addition. [ABSTRACT FROM AUTHOR]