Efficient rare earth co-doped TiO₂ electron transport layer for high-performance perovskite solar cells

Perovskite solar cells (PSCs) had received great attention as a result of their recent rapid increasing efficiency. However, the stability of PSCs is still a challenge due to the degradation of the perovskite layer caused by the high-energy ultraviolet (UV) irradiation. Inspired by the luminescent down converting ability for UV blocking and conversion as well as energy transfer between suitable rare earth (RE) ions, a planar CH₃NH₃PbI₃ perovskite solar cell using Sm³⁺ and Eu³⁺ co-doped TiO₂ electron transfer layer was designed. By optimizing the Sm³⁺ and Eu³⁺ doping concentration, the REs co-doped TiO₂ ETL combines the advantages of high electron extraction and lower interfacial recombination caused by REs introduction, a power conversion efficiency of 19.01% was obtained. In addition, benefit from the enhanced ability to convert UV light into visible light of the co-doped ETL, the PSCs can sustain higher than at least 80% of the original efficiency over 25 days of full sunlight irradiation or after 100 h of UV illumination. Moreover, since the low-temperature pulsed laser deposition was adopted in ETL fabrication process, the large area (225 mm²) and flexibility devices were further explored, with PCEs of 12.60% and 15.48%, respectively. This work indicates that Sm³⁺ and Eu³⁺ co-doped ETLs are effective and promising method to enhance the photovoltaic performance and UV stability of PSCs, which can be further applied in other PSCs with different ETLs and co-doping types.