Slot-die coating of a formamidinium-cesium mixed-cation perovskite for roll-to-roll fabrication of perovskite solar cells under ambient laboratory conditions

A deposition strategy is demonstrated for fabricating perovskite solar cells (PSCs) under ambient laboratory conditions. A nitrogen-flow treatment followed by a short (3 min), low-temperature (135 °C) anneal enables control of the nucleation and crystal growth of slot-die coated perovskite layers without the need for an anti-solvent for devices. PSCs using either glass or poly(ethylene terephthalate) (PET) substrates were prepared with an n-i-p device architecture and comprised a perovskite layer containing formamidinium and cesium cations, with or without the additive of 2-(2,3,4,5,6-pentafluorophenyl)-ethylammonium iodide (FEAI). The perovskite layer in glass-based devices was slot-die coated onto a stationary substrate with a moving coating head, whereas the deposition of the perovskite layer in PET-based devices was achieved by slot-die coating onto a moving (roll-to-roll, R2R) web using a stationary coating head. The processing conditions enabled the fabrication of PSCs displaying excellent temperature and humidity tolerance (up to 50% relative humidity). Devices fabricated on the glass substrates had power-conversion efficiencies (PCEs) of more than 18%, with PCEs of more than 15% measured for cells on the PET film substrates. The use of the FEAI additive improved the environmental stability of encapsulated glass-based PSC devices, which retained up to 70% of their initial PCE after 1000 h at maximum power point under 1-sun illumination in air. The scalability of the fabrication techniques used in this work, along with the low annealing temperature and ability to process in an ambient laboratory environment, makes this a promising approach for translation to industrial-scale R2R production processes.