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To realize high-performance perovskite solar cells (PSCs) ensuring low-cost flexible application with low energy consumption, efficient electron transport layers (ETL) that can be processed at low temperatures are desired. In this contribution, low temperature (about 70 °C) UV/ozone irradiation was applied to synthesis crystallized TiO 2 films as ETL. The UV exposure induces photo-catalytic removal of the organic ligands and spontaneous coalescence of the TiO 2 framework, resulting in excellent TiO 2 films with considerable crystallinity. UV irradiation induces both complete removal of organic media and more efficient charge collection. Accordingly, planar heterojunction (PH) PSCs with such ETL exhibited outstanding photovoltaic performance up to 17.03%, which is even higher than the value (12.98%) of counterpart device with high temperature thermal sintered TiO 2 ETL (without TiCl 4 treatment). These low temperature solution-processed TiO 2 films by facile UV irradiation are suitable for the low-cost, large yield solution process on a flexible substrate for photoelectric devices. [ABSTRACT FROM AUTHOR]

• The fluorine atom has induced electrostatic potential and dipole moment change. • Cl- doping can enhance crystallization and prevent phase change. • The champion device achieves a PCE of 16.29% and the humidity stability is improved. [Display omitted] All-inorganic CsPbI 2 Br material has attracted considerable attention due to its good balance between phase stability and absorption capacity. However, the power conversion efficiency (PCE) and device stability of CsPbI 2 Br-based perovskite solar cells (PSCs) still lag far behind those of their counterparts, mainly deriving from the notoriously poor moisture stability under humid environment and large serious charge recombination. Herein, a typical phenethylammonium chlorine (PEACl) and its fluorinated derivative 4-fluoro-phenethylammonium chlorine (F-PEACl) are individually incorporated to modify the surface of CsPbI 2 Br film to ameliorate the above issues. Benefiting from the comprehensive passivation effect of ammonium halogen, the trap states of treated CsPbI 2 Br are vastly suppressed. In particular, fluorination significantly increased the dipole moment and hydrophobic property of F-PEACl. Thus, the present CsPbI 2 Br PSC achieves a champion PCE of 16.29% with high open-circuit voltage of 1.272 V, while the reference device and PEACl-treated device yield PCEs of 14.30% and 15.64%, respectively. More importantly, the PSC with F-PEACl capping layer retains 87.2% of its initial PCE after 1000 h storage under 20% RH ambient without encapsulation. Our results reveal the underlying mechanism of performance improvement by surface passivation strategy and provide an effective approach to further boost the CsPbI 2 Br PSC efficiency and stability. [ABSTRACT FROM AUTHOR]