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.
Solution-processed perovskite films are rich in surface defects and grain boundaries, which limits their performance and stability in photovoltaic application. Surface passivation using bulky organic cations can effectively reduce the surface defects of a perovskite film without affecting its fundamental properties. Herein, the use of hydrophobic bulky aromatic molecules, namely 4-trifluoromethyl-benzylammonium iodide/bromide (CF 3 BZA-I/Br), as defectpassivators to heal the surface defects and grain boundaries of perovskite films is introduced. Owing to the presence of the trifluoromethyl (─CF 3 ) moieties, CF 3 BZA-I/Br-passivated perovskite films exhibit a hydrophobic surface with significantly fewer grain boundaries. By suppressing the surface and interfacial imperfections, CF 3 BZA-Br-treated perovskite solar cells achieve an outstanding power conversion efficiency (PCE) of 20.75%. The PCE improvement originates mainly from the reduction of trap states and nonradiative carrier recombination. The ultrathin hydrophobic barrier layer formed after passivation also shields the perovskite film surface from moisture ingress and environmental degradation, leading to improved stability of the devices. By optimizing the passivation conditions, the bulky CF 3 BZA-I/Br molecules could be the ideal defect passivators, with versatile applications in a wide variety of perovskite optoelectronics.
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