Improving the Stability of Ambient Processed, SnO2‐Based, Perovskite Solar Cells by the UV‐Treatment of Sub‐Cells

SnO2 is nowadays the widely preferred material as an electron transport layer (ETL) in most n‐i‐p planar perovskite solar cells (PSCs) due to its facility for ambient, low temperature processing, and ultraviolet (UV) stability. Most reports published so far study device stability on full cells. Herein, the role of slot‐die‐coated SnO2 on air‐processed planar PSCs by analyzing sub‐cells (indium tin oxide [ITO]/SnO2/perovskite) under UV exposure is investigated. Results from UV–vis spectroscopy, depth profiling using X‐ray diffraction measurement in grazing incidence mode (GIXRD), X‐ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy measurements show that UV treatment of ITO/SnO2/perovskite leads to a reduced electron transfer to the SnO2 layer and a gradual increase in the amount of PbI2 toward the perovskite surfaces. Subsequently, hole transport layer (HTL) and electrodes are applied on SnO2/perovskite interfaces (UV‐treated and non‐UV‐treated) and complete devices are fabricated. Device performance is compared and analyzed through J–V curves and maximum power point (MPP) tracking. Results show that devices built on a UV‐treated SnO2/perovskite interface show better stability attributed to the presence of excess PbI2 resulting in a passivation effect. Challenges in uniform film formation of slot‐die‐coated SnO2 and potential solutions using a polymeric additive are also highlighted. The article studies SnO2's role in the stability of air‐processed planar perovskite solar cells. UV treatment of sub‐cells (500 h N2 environment) speeds up the depletion of perovskite films, leading to excess PbI2 formation at the perovskite surfaces. This inadvertently leads to full device stabilization through passivation as seen in maximum power point (MPP) measurements of perovskite solar cells incorporating UV‐treated sub‐cells.