Mixed halide perovskites are one of the promising candidates in developing solar cells and LEDs, among others applications due to their tunable optical properties. Nonetheless, photoinduced phase segregation, by forming segregated Br-rich and I-rich domains, limits the overall applicability. We tracked the phase segregation with increasing crystalline sizes of CsPbBr3-xIx and their photoluminescence under continuous-wave laser irradiation (405 nm, 10 mW cm-2), and observed the occurrence of the phase segregation from the threshold size of 46 ± 7 nm. This results have an outstanding agreement with the diffusion length (45.8 nm) calculated also experimentally from the emission lifetime, segregation rates. Furthermore, through Kelvin probe forced microscopy, we confirmed the correlation between the phase segregation and the reversible halide ion migration among grain center/boundaries. These results open a way to achieve segregation-free mixed halide perovskites and improve their performances in optoelectronic devices.

Inspired by the outstanding optoelectronic properties reported for all-inorganic halide perovskite quantum dots (QDs), we have evaluated the potential of these materials towards the photocatalytic and photoelectrochemical degradation of organic compounds, taking the oxidation of 2-mercaptobenzothiazole (MBT) as a proof-of-concept. First, we determined electrochemically the energy levels of dispersions of perovskite QDs with different bandgap induced by the different ratios between halides (Br and I) and metallic cations (Pb and Sn). Then, we select CsPbBr₃ QDs to demonstrate the photocatalytic and photoelectrochemical oxidation of MBT, confirming that hole injection takes place from CsPbBr₃ QDs to MBT, resulting in the total degradation of MBT as evidenced by Electro Spray Mass Spectrometry analyses. Although the stability and toxicity of these QDs are major issues to address in the near future, the results obtained in the present study open promising perspectives for the implementation of solar-driven catalytic strategies based on these fascinating materials.

Due to the high industrial interest for perovskite-based photovoltaic devices, there is an urgent need to fabricate them under ambient atmosphere, not limited to low relative humidity (RH) conditions. The formamidinium lead iodide (FAPI) perovskite α-black phase is not stable at room temperature and is challenging to stabilize in an ambient environment. In this work, we show that pure FAPI perovskite solar cells (PSCs) have a dramatic increase of device long-term stability when prepared under ambient air compared to FAPI PSCs made under nitrogen, both fabricated with N-methylpyrrolidone (NMP). The T₈₀ parameter, the time in which the efficiency drops to 80% of the initial value, increases from 21 (in N₂) to 112 days (in ambient) to 145 days if PbS quantum dots (QDs) are introduced as additives in air-prepared FAPI PSCs. Furthermore, by adding methylammonium chloride (MACl) the power conversion efficiency (PCE) reaches 19.4% and devices maintain 100% of the original performance for at least 53 days. The presence of Pb–O bonds only in the FAPI films prepared in ambient conditions blocks the propagation of α- to δ-FAPI phase conversion. Thus, these results open the way to a new strategy for the stabilization in ambient air toward perovskite solar cells commercialization.

Hot-injection has become the most widespread method used for the synthesis of perovskite quantum dots (QDs) with enormous interest for application in optoelectronic devices. However, there are some aspects of the chemistry involved in this synthesis that have not been completely investigated. In this work, we synthesized ultra-high stable CsPbI₃ QDs for more than 15 months by controlling two main parameters: synthesis temperature and the concentration of capping ligands. By increasing the capping ligand concentration during the QD synthesis, we were able to grow CsPbI₃ in a broad range of temperatures, improving the photophysical properties of QDs by increasing the synthesis temperature. We achieved the maximum photoluminescence quantum yield (PLQY) of 93% for a synthesis conducted at 185 °C, establishing an efficient surface passivation to decrease the density of non-radiative recombination sites. Under these optimized synthesis conditions, deep red LEDs with an External Quantum Efficiency (EQE) higher than 6% were achieved. The performance of these LEDs is higher than that of the reported CsPbI₃ QD-LEDs containing standard capping agents, without additional elements or further element exchange. We show that it is possible to produce stable CsPbI₃ QDs with high PLQY and red emission beyond the requirement of the Rec. 2020 standards for red color.