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

Abstract

Tin-perovskite solar cells (Sn-PSCs) have low energy conversion efficiency and stability due to facile oxidation of Sn 2+ 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 −NH 2 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.

Defect Modulation via SnX2 Additives in FASnI3 Perovskite Solar Cells

“…The V bi extracted for the FASnI 3 + SnF 2 , FASnI 3 + SnCl 2 , and FASnI 3 + SnBr 2 devices is 0.63, 0.54, and 0.47 V, respectively. The calculated N i of FASnI 3 + SnF 2 , FASnI 3 + SnCl 2 , and FASnI 3 + SnBr 2 devices is 9.05 × 10 15 , 1.38 × 10 16 , and 1.11 × 10 16 cm –3 , respectively, which are comparable to the literature values determined by capacitance and Hall measurements. ,,− The lower N i of FASnI 3 + SnF 2 relative to with SnCl 2 and SnBr 2 supports that the formation of Sn 4+ is most suppressed, leading to less background carriers (holes) and lower defect densities, which agrees with the UPS and XPS measurements. Dark J–V measurements (Figure S9) also support the decreased hole density, with decreased dark current densities for FASnI 3 + SnF 2 compared to those with other SnX 2 additives.…”

Multi-functional molecule advancing the efficiency of pure 3D FASnI3 perovskite solar cells based on the tin tetraiodide reduction method

“…S7a,† the PHPA molecule not only contains a strongly reducing hydrazide group that inhibits the oxidation of Sn 2+ , but also carries a sulfonic acid group (–SO 3 H) that may interact with Sn 2+ in solution via coordination interactions and electrostatic attraction, a similar mechanism of what is found in the literature with the exploitation of bidentate ligands. 34–36 This might happen because the PHPA molecule shows a zwitterionic behavior (see Fig. S7b†) which in polar organic solvents like DMSO and DMF (where PHPA has good solubility) can be maintained during film processing, as already reported elsewhere.…”

Defect passivation in methylammonium/bromine free inverted perovskite solar cells using charge-modulated molecular bonding

“…To explore the spatial distributions of molecular passivator, time-of-flight secondary ion mass spectrometry (ToF-SIMS) 32 , 45 , 59 was used to track the ionic distribution of PEDA 2+ and PZD 2+ in the HP. The characteristic ionic species are shown in Fig.…”