Elucidating Interfacial Limitations Induced by Tin Oxide Electron Selective Layer Grown by Atomic Layer Deposition in N-I-P Perovskite-Based Solar Cells

Fabricating tin dioxide (SnO2) electron selective layers (ESL) by atomic layer deposition (ALD) can be of high interest for perovskite-based solar cell development since it offers a number of advantages over solution-based processes. However, ALD-grown SnO2 ESL has usually been reported to yield limited cell efficiency compared to solution-processed SnO2 ESL, without the causes being clearly identified. This is why we here conduct a thorough interface study using a set of complementary techniques. For this purpose, ALD-grown SnO2 thin films are characterized in a systematic comparison with reference solution-processed SnO2. Energetics analysis by ultraviolet photoelectron spectroscopy (UPS) points out an unfavorable band bending at the ALD-grown SnO2/perovskite interface. Chemical characterization by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and hard X-ray photoelectron spectroscopy (HAXPES) profiling unveils an unexpected lack of oxygen at the ALD-grown SnO2/perovskite interface, which may play a direct role in observed performance limitations.