Ce-Doped SnO<sub>2</sub> Electron Transport Layer for Minimizing Open Circuit Voltage Loss in Lead Perovskite Solar Cells
Shamim Ahmmed, Yulu He, Md. Emrul Kayesh, Md. Abdul Karim, Kiyoto Matsuishi, Ashraful Islam
Abstract
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%.