Metal halide perovskite nanocrystals (NCs) are attractive materials for optoelectronics. However, further improvements in stability, reproducibility, and photoluminescence quantum yield (Φ PL ) are essential for enabling future applications. Inadequate surface passivation is a major cause of instability, irreproducibility, and less than unity Φ PL . Herein, we probe the influence of multiple ligand binding groups on the colloidal stability and Φ PL of CsPbBr 3 nanocrystals (NCs). We find that post-synthetic treatment with dodecanethiol reproducibly yields highly stable NCs with near-unity Φ PL for a range of synthetic conditions and initial Φ PL of the as-synthesized NCs. A mechanistic investigation shows that thiol addition leads to thioether formation via the thiol−ene reaction with octadecene, oleic acid, and oleylamine. Both thiolates and thioethers are suspected to bind to undercoordinated Pb atoms on the NC surfaces, and this surface binding can be rapidly accelerated through exposure to blue or UV light. Furthermore, we show that metallic Pb nanoparticles appear in many batches of synthesized CsPbBr 3 NCs and that dodecanethiol addition eliminates these metallic Pb particles.

crystallization caused low-quality films and Sn 2+ oxidation induced p-doping. [4,5] These are accompanied by defects generated in perovskites, which always leads to quick reduction of the PCE and durability of tin-lead PSCs. [6] Tremendous efforts have been made to reduce the intrinsic defects in Sn-Pb PSCs by developing perovskite processing methods and customizing additives. [7][8][9][10] With advances in past years, the PCE of Sn-Pb PSCs has been elevated to more than 23%, which is still smaller but close to the Pb-based counterparts. [11,12] However, much larger challenges remain in the long-term stability of Sn-Pb PSCs.One concerning observation is that Sn-Pb perovskite photovoltaic devices still degrade much faster under light than Pb perovskites even when they are stored in inert condition or fully encapsulated to separate moisture and oxygen. [13] Recent studies show that they are not only caused

Tin–lead (Sn–Pb) narrow‐bandgap (NBG) perovskites show great potential in both single‐junction and all‐perovskite tandem solar cells. Sn–Pb perovskite solar cells (PSCs) are still limited by low charge collection efficiency and poor stability. Here, a ternary Sn (II) alloy of SnOCl is reported as the hole‐transport material (HTM) with a work function of 4.95 eV for Sn–Pb PSCs. The solution‐processed SnOCl layer has a texture structure that not only reduces the optical loss of the devices, but also changes grain growth of Sn–Pb perovskites and boosts the carrier diffusion length to 3.63 µm. The formation of small perovskite grains at the HTM/perovskite interface is suppressed. These result in an almost constant internal quantum efficiency (IQE) of 96 ± 2% across the absorption spectrum of Sn–Pb perovskites. The SnOCl HTM significantly enhances the stability of Sn–Pb PSCs with 87% of its initial efficiency retained after 1‐sun illumination for 1200 h, and keeps 85% efficiency under 85 °C thermal stress for 1500 h. The hybrid HTM further improves the stabilized efficiencies of single‐junction Sn–Pb PSCs and all‐perovskite tandem solar cells to 23.2% and 25.9%, respectively. This discovery opens an avenue to the multicomponent metal alloys as HTM in PSCs.

The formation of voids in perovskite films close to the buried interface has been reported during film deposition. These voids are thought to limits the efficiency and stability of perovskite solar cells (PSCs). Here, we studied the voids formed during operation in perovskite films that were optimized during the solution deposition process to avoid voids. New voids formed during operation are found to assemble along grain boundaries at the bottom interface, caused by the loss of residual solvent and conversion of amorphous phase to crystalline phase. Unexpectedly, the formation of these voids did not negatively affect the stability of PSCs. Decreasing the amorphous region in perovskites by thermal annealing decreased the positive iodide interstitial density, and improved the light stability of PSCs. The annealed devices maintained 90% of their initial efficiency and light soaking for 1900 hours at open circuit condition under 1-sun illumination at 50°C.