Alleviating Defect and Oxidation in Tin Perovskite Solar Cells Using a Bidentate Ligand

Tin-perovskite solar cells (Sn-PSCs) have low energy conversion efficiency and stability due to facile oxidation of Sn2+ during precursor solution preparation and film growth. Herein, we introduced formohydrazide (FHZ) as a bidentate ligand into the Sn-halide perovskite (Sn-HaP) to improve the optoelectronic properties. This approach is found to be effective for the suppression of Sn-oxidation and interfacial energy band modulation. The depth profile distribution confirmed that the FHZ additive is primarily located on surfaces and the hole transport layer (HTL)/Sn-HaP interface with partly capping at the grain boundaries, which offers a reducing ambient in the Sn-HaP film. Therefore, the device with FHZ demonstrated a device efficiency of 12.87% (9.93% control) with enhanced open circuit voltage from ∼0.734 to 0.874 V and improved operational device stability. The device analysis suggests that the FHZ additive alleviates the bulk and interface defect in the Sn-PSC with −NH2 and −O═C bidentate bonding to Sn-HaP, which is supported by theoretical calculations. Thus, this work corroborates the importance of multidentate ligands for modulating the film morphology and defect chemistry in the Sn-perovskite for high efficiency and superior device stability.