Rapid Scalable Processing of Tin Oxide Transport Layers for Perovskite Solar Cells

Abstract

The development of scalable deposition methods for perovskite solar cell materials is critical to enable the commercialization of this nascent technology. Herein, we investigate the use and processing of nanoparticle SnO₂ films as electron transport layers in perovskite solar cells and develop deposition methods for ultrasonic spray coating and slot-die coating, leading to photovoltaic device efficiencies over 19%. The effects of postprocessing treatments (thermal annealing, UV ozone, and O₂ plasma) are then probed using structural and spectroscopic techniques to characterize the nature of the np-SnO₂/perovskite interface. We show that a brief "hot air flow" method can be used to replace extended thermal annealing, confirming that this approach is compatible with high-throughput processing. Our results highlight the importance of interface management to minimize nonradiative losses and provide a deeper understanding of the processing requirements for large-area deposition of nanoparticle metal oxides.

Figure 1

np-SnO₂ device structure and performance. (a) Illustration of the n–i–p layer architecture with a photograph of a completed device inset. (b) Cross-sectional SEM image of a completed device showing densely packed perovskite grains and ultrathin np-SnO₂ layer. (c) Histogram of all spin-coated device efficiencies (forward and reverse sweep), showing excellent reproducibility. Champion cell performance is illustrated by (d) a current–voltage sweep and (e) stabilized device performance at the J–V determined MPP.

Figure 2

Scheme illustrating the optimized np-SnO₂ drying process across the UVO-treated ITO surface: (i) spray-coating, (ii) fast reticulation, (iii) dry film with poor uniformity, (iv) ideal wet film, and (v) drying proceeds across the substrate.

Figure 3

AFM height maps for uniformity and roughness of (a) ITO, (b) spin-coated and (c) spray-coated np-SnO₂ layers. Profilometric mapping of completed devices using spray-deposited np-SnO₂ with (d) IPA/H₂O mixed solvent and (e) H₂O-only solution; here, np-SnO₂ layer inhomogeneity in the IPA/H₂O cast film leads to pinholes in subsequent layers. (f) J–V curve for the best-performing spray np-SnO₂ device.

Figure 4

In-plane linecuts and Guinier–Porod fitting of GISAXS from np-SnO₂ layers with different annealing conditions; as-deposited, 30 min 150 °C annealed, and HAF for 1, 2, and 5 min. 2D GISAXS patterns for all samples are shown in Figure S13.

Figure 5

J–V curves for the best-performing cells using np-SnO₂ treated with 1 min 120 °C drying and either 15 min UVO or 5 min O₂ plasma prior to perovskite deposition. Key sweep parameters are inset (full parameters in Table S4), with the O₂ plasma-treated np-SnO₂ device exhibiting lower V_OC and increased hysteresis.

Figure 6

Understanding the effect of UVO and O₂ plasma treatments. (a) Electronic structure at the np-SnO₂ surface with the Fermi level (E_F) from UPS measurements, valence band from UPS and XPS and estimated conduction band from the optical band gap. (b) Stabilized light-V_OC measurements for 120 + UVO and 120 + O₂ devices, showing reduced V_OC for the plasma treatment. Apparent n_id from linear fits are shown, and in the O₂ plasma case, behavior indicates increased nonradiative recombination at the ETL interface.^,

Figure 7

Photovoltaic performance for devices prepared using fast processing: spray coating, 1 min HAF, and UVO treatment. (a) Reverse and forward sweep efficiencies for 19 operational cells, (b) J–V sweep, and (c) SPO of the best-performing cell.