Benefitting from methylene blue dye molecule for improving performance of perovskite photovoltaics

Tin oxide (SnO₂) has great potential as an electron transport layer (ETL) for low-cost and high-performance n-i-p-type perovskite solar cells (PSCs) due to its low annealing temperature, desirable optical transparency, and good n-type behaviors. However, the existence of defects at the surface and the relatively low charge transport/extraction behavior of SnO₂ ETL restrict its widespread applications in PSCs despite the advantages of SnO₂-based ETL. In this study, surface engineering is performed by modifying the SnO₂ ETL layer with methylene blue (MB) dye with multiple functions in order to improve the surface contact of the SnO₂ surface and decrease the defect states for better photovoltaic performance in PSCs. The comprehensive and systematic analyses demonstrate that after the modification of the SnO₂ ETL, oxygen vacancies and surface defects of the SnO₂ surface are reduced. As a result of these improvements, the device with the MB-SnO₂-based ETL presents a power conversion efficiency (PCE) of 21.47 % with a short-circuit current (J_SC) of 24.51 mA/cm², an open-circuit voltage (V_OC) of 1.109 V, and a fill factor (FF) of 0.79 compared to about 19.77 % of the reference cell. Moreover, the devices under 40–50 % humidity conditions at room temperature show that the devices that were treated with MB maintained over 80 % of their initial efficiency after 600 h, whereas the reference PSC retained only ∼67 % of its initial efficiency. It is believed that this current report allocates an efficient surface engineering strategy via dye molecules for high-efficiency and stable PSCs.