Room‐Temperature Spray Deposition of Large‐Area SnO₂ Electron Transport Layer for High Performance, Stable FAPbI₃‐Based Perovskite Solar Cells

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.

Nonplanar Spray-Coated Perovskite Solar Cells

“…We note that the efficiency of the devices presented here was partly limited by hysteresis effects that can be suppressed through the use of both bulk and interfacial passivation techniques . We also expect further enhancements in device efficiency through the use of surfactants to improve surface coverage of the perovskite layer and through optimization of the processes used to spray cast the charge transport layers. , We note that spray coating can be used to rapidly coat large areas at high speed, potentially allowing PSCs to be fabricated over relatively large-area substrates . We expect the combination of spray coating with device modularization techniques (e.g., via laser patterning) to allow spray-coated modules to be fabricated over very large areas.…”

Intercalation of Ammonium Cationic Ligands Enabled Grain Surface Passivation in Sequential‐Deposited Perovskite Solar Cells

“…The high‐resolution TEM (HRTEM) image in Figure 3b reveals that these newly formed nanograin has lattice fringes with d ‐spacing values of 0.21, 0.22, and 0.32 nm, which can be indexed to the (314), (224), and (220) diffraction planes of cubic perovskite crystal, respectively. [ 37 ] This indicates that the nanograins have a 3D cubic perovskite phase. Beneath the film surface, lattice fringes with a d ‐spacing of 0.63 nm corresponding to the main (110) planes of the 3D perovskite were also detected, which is in good agreement with the XRD results.…”

“…Besides the C–F 3 peak, the C 1 s spectra of both perovskite films also contain the signature C–C peak (BE ≈284.6 eV), which arises from the surface adsorbed amorphous carbon, and the CNH 2 + peak (BE ≈287.8 eV) associated with the FA component in the perovskite. [ 37 ] In the case of the target film, the increased signal of the C–C peak arose due to the presence of the phenyl group in the CF 3 BZA + cation on the film surface. Similarly, the minor shift of the C–C peak to a higher BE is attributable to the increasing number of highly electronegative fluorine (F) atoms in the CF 3 BZA cations which draws electrons from the neighboring carbon atoms.…”

“…The target film also has a deeper HOMO level than the control film which could suppress the recombination of charge carriers at the perovskite/HTL interface for better device performance. [ 37 ] The XPS and UPS results prove that the intercalation of CF 3 BZAI is highly beneficial to the chemical composition and energy band alignment of the perovskite film, which can lead to considerable changes of the device performance of PSCs.…”

“…The SnO 2 solution was first filtered through a polypropylene filter (0.45 um) and then spray‐coated onto the ITO substrates at room temperature using a recipe similar to that reported in our previous work. [ 37 ] The SnO 2 films were postannealed at 150 °C for 30 min in ambient air. A perovskite absorber film was prepared via a two‐step sequential deposition technique, as demonstrated in our previous work, with some modifications.…”