Enhancing efficiency and decreasing photocatalytic degradation of perovskite solar cells using a hydrophobic copper-modified titania electron transport layer

The electron transport layer (ETL) plays a pivotal role in obtaining perovskite solar cells (PSCs) with high power conversion efficiency (PCE). Titanium dioxide is a widely used ETL, however it suffers from low electron mobility, poor conductivity and may act as a photocatalyst of chemical reactions leading to degradation of the perovskite. Herein, copper cations employed to modify the titania ETL of PSCs, mitigate the photocatalytic action of the compact layer, increase its conductivity and electron mobility, adjust favorably the energy levels, improve the ETL/perovskite interface, thus enhance perovskite’s light absorption and provoke passivation of the perovskite surface trap states. The investigation of structural and surface chemistry properties revealed the uniform distribution of Cu1+ in TiO2 and confirmed the determining role of copper in the fast extraction of the photogenerated charge carriers to the adjacent electrode. As a result, the champion planar PSCs based on the hydrophobic Cu-TiO2 ETL showed a 18.15 % PCE outperforming the reference devices (based on pristine TiO2 ETL) which showed a PCE equal to 15.78 %. The results followed the same trend also in the case of mesoporous PSCs, proving the universality of our approach. Finally, aging tests confirmed that the copper-modified devices showed higher stability in comparison with the non-modified ones retaining the 53 % of the initial PCE value after 51 days of storage in relative humidity (RH = 25 %) and dark conditions. Photostability experiments proved that the Cu-TiO2 based devices showed remarkable robustness and retained approximately 91 % of their initial PCE, even after 5 h under continuous UV stress. These results are associated with the suppression of the photocatalytic activity of the ETL and open new perspectives for improving the performance of TiO2-based PSCs.