Annealing free tin oxide electron transport layers for flexible perovskite solar cells

Electron transport layer (ETL) is a key component in the perovskite solar cells (PSCs). Low temperature, even room temperature deposition technique for ETLs is especially intriguing for flexible solar cell fabrication on polymer substrates . Here, we proposed a facile amine gas fuming strategy to prepare SnO 2 ETLs at room temperature without thermal annealing. It is found that the SnO 2 films treated with methylamine or other amine gases are smoother and more compact than the SnO 2 films with thermal annealing. A base-catalyzed densification mechanism is proposed that the SnO 2 colloidal is converted into compact film through particle connections and attachments facilitated by basic amine gas treatments. XRD , FTIR and TEM were used to verify the densification mechanism. With methylamine treated SnO 2 ETLs, the rigid and flexible PSCs achieved high PCEs of 20.36% and 19.80%, respectively. The flexible PSCs with the annealing free SnO 2 ETLs showed excellent flexibility with 94.5% of the initial PCE remaining after 3000 bending cycles. The amine fuming method provides a new and facile way for annealing free deposition of charge transport layers for flexible solar cells and optoelectronics .