Ce-Doped SnO 2 Electron Transport Layer for Minimizing Open Circuit Voltage Loss in Lead Perovskite Solar Cells.

In the planar heterostructure of perovskite-based solar cells (PSCs), tin oxide (SnO 2 ) is a material that is often used as the electron transport layer (ETL). SnO 2 ETL exhibits favorable optical and electrical properties in the PSC structures. Nevertheless, the open circuit voltage ( V OC ) depletion occurs in PSCs due to the defects arising from the high oxygen vacancy on the SnO 2 surface and the deeper conduction band (CB) energy level of SnO 2 . In this research, a cerium (Ce) dopant was introduced in SnO 2 (Ce-SnO 2 ) to suppress the V OC loss of the PSCs. The CB minimum of SnO 2 was shifted closer to that of the perovskite after the Ce doping. Besides, the Ce doping effectively passivated the surface defects on SnO 2 as well as improved the electron transport velocity by the Ce-SnO 2 . These results enabled the power conversion efficiency (PCE) to increase from 21.1% (SnO 2 ) to 23.0% (Ce-SnO 2 ) of the PSCs (0.09 cm 2 active area) with around 100 mV of improved V OC and reduced hysteresis. Also, the Ce-SnO 2 ETL-based large area (1.0 cm 2 ) PSCs delivered the highest PCE of 22.9%. Furthermore, a V OC of 1.19 V with a PCE of 23.3% was demonstrated by Ce-SnO 2 ETL-based PSCs (0.09 cm 2 active area) that were treated with 2-phenethylamine hydroiodide on the perovskite top surface. Notably, the unencapsulated Ce-SnO 2 ETL-based PSC was able to maintain above 90% of its initial PCE for around 2000 h which was stored under room temperature condition (23-25 °C) with a relative humidity of 40-50%.