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

Tin-perovskitesolar cells (Sn-PSCs) have low energy conversionefficiency and stability due to facile oxidation of Sn2+ during precursor solution preparation and film growth. Herein, weintroduced formohydrazide (FHZ) as a bidentate ligand into the Sn-halideperovskite (Sn-HaP) to improve the optoelectronic properties. Thisapproach is found to be effective for the suppression of Sn-oxidationand interfacial energy band modulation. The depth profile distributionconfirmed that the FHZ additive is primarily located on surfaces andthe hole transport layer (HTL)/Sn-HaP interface with partly cappingat the grain boundaries, which offers a reducing ambient in the Sn-HaPfilm. Therefore, the device with FHZ demonstrated a device efficiencyof 12.87% (9.93% control) with enhanced open circuit voltage from similar to 0.734 to 0.874 V and improved operational device stability.The device analysis suggests that the FHZ additive alleviates thebulk and interface defect in the Sn-PSC with -NH2 and -O=C bidentate bonding to Sn-HaP, which is supportedby theoretical calculations. Thus, this work corroborates the importanceof multidentate ligands for modulating the film morphology and defectchemistry in the Sn-perovskite for high efficiency and superior devicestability.