Recently, lead-free Sn-based perovskite light-emitting diodes (PeLEDs) have attracted wide attention due to their near-infrared emission and environmental friendliness. However, desired Sn2+ is easily oxidized to Sn4+ in the crystallization process, resulting in defects and intrinsically p-doped properties in the perovskite films. The uncontrollable oxidation affects the charge injection balance and radiative recombination, leading to poor device performance. Herein, a bi-functional conductive molecular, 2,7-bis(diphenylphosphoryl)-9,9 '-spirobifluorene (SPPO13) with two PO functional groups, is used to interact with perovskite to passivate defects and suppress the oxidation of Sn2+. Moreover, the SPPO13 modification layer inserted between the perovskite emitter and the electron transport layer can regulate the carrier injection and transport, thus promoting the charge balance. As a result, the high-performance near-infrared CsSnI3 PeLEDs with a record external quantum efficiency (EQE) of 6.60% and ultra-low efficiency roll-off are achieved. The work provides a novel approach to regulate defect passivation and charge transport for efficient Sn-based PeLEDs. A bi-functional conductive molecular, 2,7-bis(diphenylphosphoryl)-9,9 '-spirobifluorene with two PO functional groups, is introduced to interact with perovskite to passivate defects and promote charge balance. As a result, the high-performance near-infrared CsSnI3 perovskite light-emitting diodes (PeLEDs) with a record external quantum efficiency of 6.60% and ultra-low efficiency roll-off are achieved, providing a novel approach for preparing efficient Sn-based PeLEDs.image

Due to their unique photoelectric properties, nontoxic tin-based perovskites are emerging candidates for efficient near-infrared LEDs. However, the facile oxidation of Sn2+ and the rapid crystallization rate of tin-based perovskites result in suboptimal film quality, leading to inferior efficiencies of tin-based perovskite light-emitting diodes (Pero-LEDs). In this study, we investigate the influence of commonly used solvents on the quality of the CsSnI3 films. Remarkably, DMSO exhibits a stronger interaction with SnI2, forming a stable intermediate phase of SnI2·3DMSO. This intermediate effectively inhibits the oxidation of Sn2+ and slows down the crystallization rate, bringing in lower defect state density and higher photoluminescence quantum yield of the prepared perovskite films. Consequently, the corresponding Pero-LEDs achieve a maximum external quantum efficiency (EQE) of 5.6%, among the most efficient near-infrared Pero-LEDs. In addition, the device processes ultra-low efficiency roll-off and high reproducibility. Our research underscores the crucial role of solvent-perovskite coordination in determining film quality. These findings offer valuable guidance for screening solvents to prepare highly efficient and stable tin-based perovskites.

Eco-friendly Sn-based perovskites show significant potential for high-performance second near-infrared window light-emitting diodes (900 nm - 1700 nm). Nevertheless, achieving efficient and stable Sn-based perovskite second near-infrared window light-emitting diodes remains challenging due to the propensity of Sn2+ to oxidize, resulting in detrimental Sn4+-induced defects and compromised device performance. Here, we present a targeted strategy to eliminate Sn4+-induced defects through moisture-triggered hydrolysis of tin tetrahalide, without degrading Sn2+ in the CsSnI3 film. During the moisture treatment, tin tetrahalide is selectively hydrolyzed to Sn(OH)4, which provides sustained protection. As a result, we successfully fabricate second near-infrared window light-emitting diodes emitting at 945 nm, achieving a performance breakthrough with an external quantum efficiency of 7.6% and an operational lifetime reaching 82.6 h. Guan et al. report a strategy of moisture-triggered selective hydrolysis of Sn4+ into Sn(OH)4, eliminating Sn4 + -induced defects in tin-based perovskites and enhancing the electron injection in NIR-II LED devices with peak emission of 945 nm and external quantum efficiency of 7.6%.

Metal halide perovskites are emerging as promising candidates for next-generation display and lighting technologies.