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Abstract:

Oleylamine and oleic acid are common organic capping ligands used in the hot injection preparation of perovskite quantum dots (QDs). Their labile nature is responsible for the poor colloidal stability and conductivity that affect the performance of perovskite QD light-emitting diodes (LEDs). We introduced 4-trifluoro phenethylammonium iodide (CF₃PEAI) directly in the synthesis and found that CF₃PEAI efficiently modified the I^- vacancy defects on the QD surface and partially substituted the surface capping ligand oleylamine. The strong electron pulling ability of F in CF₃PEAI results in a more positive -NH₃⁺ terminal compared to that of PEAI, which promotes tight bonding of CF₃PEAI on the surface of CsPbI₃ QDs. As a result, we achieved bright QDs with a photoluminescence quantum yield of 92% and efficient red LEDs. The maximal luminance was improved to 4550 cd m^-2 for 685 nm red light, which was nearly 4.6-fold of the LEDs with plain CsPbI₃ QDs. Additionally, the peak external quantum efficiency reached 12.5%.

Abstract:

The performance and scalability of perovskite solar cells (PSCs) is highly dependent on the morphology and charge selectivity of the electron transport layer (ETL). This work demonstrates a high-speed (1800 mm min^-1 ), room-temperature (25 °C-30 °C) deposition of large-area (62.5 cm² ) tin oxide films using a multi-pass spray deposition technique. The spray-deposited SnO₂ (spray-SnO₂ ) films exhibit a controllable thickness, a unique granulate morphology and high transmittance (≈85% at 550 nm). The performance of the PSC based on spray-SnO₂ ETL and formamidinium lead iodide (FAPbI₃ )-based perovskite is highly consistent and reproducible, achieving a maximum efficiency of ≈20.1% at an active area (A) of 0.096 cm² . Characterization results reveal that the efficiency improvement originates from the granular morphology of spray-SnO₂ and high conversion rate of PbI₂ in the perovskite. More importantly, spray-SnO₂ films are highly scalable and able to reduce the efficiency roll-off that comes with the increase in contact-area between SnO₂ and perovskite film. Based on the spray-SnO₂ ETL, large-area PSC (A = 1.0 cm² ) achieves an efficiency of ≈18.9%. Furthermore, spray-SnO₂ ETL based PSCs also exhibit higher storage stability compared to the spin-SnO₂ based PSCs.