Bilayer of Atomic Layer Deposition and Solution‐Processed Tin Dioxide as a Pathway to High‐Performance Electron Transport Layers for Perovskite Solar Cells

This perspective explores the transformative potential of atomic layer deposition (ALD) in fabricating high‐performance tin dioxide (SnO 2 ) electron transport layers (ETLs) for perovskite solar cells (PSCs). ALD ensures conformal coatings with atomic‐scale precision, reducing surface roughness and recombination sites while enhancing the structural and electronic properties of complementary SnO 2 layers. Furthermore, ALD's capacity to optimize energy‐level alignment and foster high‐quality perovskite crystallization improves charge transport, reduces trap‐assisted recombination, and enhances device performance. Despite the advantages of ALD, most high‐performance ALD SnO 2 ‐based PSCs are combined with sol–gel deposition of SnO 2 , chemical bath deposition of SnO 2 , or nanoparticle SnO 2 ( np ‐SnO 2 ), commonly referred to as bilayer ETLs. Bilayer ETLs address key challenges, including surface uniformity, defect mitigation, and energy alignment, which significantly impact PSC efficiency and stability. This perspective highlights the recent advances in ALD SnO 2 /solution‐processed SnO 2 (SP‐SnO 2 ) bilayer ETLs in PSCs and explores the mechanisms for the superior photovoltaic performance of these bilayer approaches compared to single‐layer ALD SnO 2 . The perspective also identifies remaining challenges, including interface defects and scalability issues, and explores solutions like in situ passivation and interfacial engineering.