Band Alignment Engineering between Planar SnO₂ and Halide Perovskites via Two-Step Annealing

Managing defects in SnO₂ is critical for improving the power conversion efficiency (PCE) of halide perovskite-based solar cells. However, typically reported SnO_2-based perovskite solar cells have inherent defects in the SnO₂ layer, which lead to a lower PCE and hysteresis. Here, we report that a dual-coating approach for SnO₂ with different annealing temperatures can simultaneously form a SnO₂ layer with high crystallinity and uniform surface coverage. Along with these enhanced physical properties, the dual-coated SnO₂ layer shows favorable band alignment with a mixed halide perovskite. After careful optimization of the dual-coating method, the average PCE of the perovskite solar cell based on the dual-coated SnO₂ layer increases from 18.07 to 19.23% with a best-performing cell of 20.03%. Note that a facile two-step coating and annealing method can open new avenues to develop SnO₂-based perovskite solar cells with stabilized and improved photovoltaic performances.