Huimin Su

Solution‐processed perovskite (PSC) solar cells have achieved extremely high power conversion efficiencies (PCEs) over 20%, but practical application of this photovoltaic technology requires further advancements on both long‐term stability and large‐area device demonstration. Here, an additive‐engineering strategy is developed to realize a facile and convenient fabrication method of large‐area uniform perovskite films composed of large crystal size and low density of defects. The high crystalline quality of the perovskite is found to simultaneously enhance the PCE and the durability of PSCs. By using the simple and widely used methylammonium lead iodide (MAPbI 3 ), a certified PCE of 19.19% is achieved for devices with an aperture area of 1.025 cm 2 , and the high‐performing devices can sustain over 80% of the initial PCE after 500 h of thermal aging at 85 °C, which are among the best results of MAPbI 3 ‐based PSCs so far.

Unreacted lead iodide is commonly believed to be beneficial to the efficiency of methylammonium lead iodide perovskite based solar cells, since it has been proposed to passivate the defects in perovskite grain boundaries. However, it is shown here that the presence of unreacted PbI 2 results in an intrinsic instability of the film under illumination, leading to the film degradation under inert atmosphere and faster degradation upon exposure to illumination and humidity. The perovskite films without lead iodide have improved stability, but lower efficiency due to inferior film morphology (smaller grain size, the presence of pinholes). Optimization of the deposition process resulted in PbI 2 ‐free perovskite films giving comparable efficiency to those with excess PbI 2 (14.2 ± 1.3% compared to 15.1 ± 0.9%) Thus, optimization of the deposition process for PbI 2 ‐free films leads to dense, pinhole‐free, large grain size perovskite films which result in cells with high efficiency without detrimental effects on the film photostability caused by excess PbI 2 . However, it should be noted that for encapsulated devices illuminated through the substrate (fluorine‐doped tin oxide glass, TiO 2 film), film photostability is not a key factor in the device degradation.

In this contribution, we conceptually present a new avenue to construction of molecular functional materials with high performance of circularly polarised luminescence (CPL) in the condensed phase. A molecule (1) containing luminogenic silole and chiral sugar moieties was synthesized and thoroughly characterized. In a solution of 1, no circular dichroism (CD) and fluorescence emission are observed, but upon molecular aggregation, both the CD and fluorescence are simultaneously turned on, showing aggregation-induced CD (AICD) and emission (AIE) effects. The AICD effect is supported by the fact that the molecules readily assemble into right-handed helical nanoribbons and superhelical ropes when aggregated. The AIE effect boosts the fluorescence quantum efficiency (Φ _F) by 136 fold (Φ _F, ∼0.6% in the solution versus ∼81.3% in the solid state), which surmounts the serious limitations of aggregation-caused quenching effect encountered by conventional luminescent materials. Time-resolved fluorescence study and theoretical calculation from first principles conclude that restriction of the low-frequency intramolecular motions is responsible for the AIE effect. The helical assemblies of 1 prefer to emit right-handed circularly polarised light and display large CPL dissymmetry factors (g _em), whose absolute values are in the range of 0.08-0.32 and are two orders of magnitude higher than those of commonly reported organic materials. We demonstrate for the first time the use of a Teflon-based microfluidic technique for fabrication of the fluorescent pattern. This shows the highest g _em of -0.32 possibly due to the enhanced assembling order in the confined microchannel environment. The CPL performance was preserved after more than half year storage under ambient conditions, revealing the excellent spectral stability. Computational simulation was performed to interpret how the molecules in the aggregates interact with each other at the molecular level. Our designed molecule represents the desired molecular functional material for generating efficient CPL in the solid state, and the current study shows the best results among the reported organic conjugated molecular systems in terms of emission efficiency, dissymmetry factor, and spectral stability.

Solar cells incorporating lead halide-based perovskite absorbers can exhibit impressive power conversion efficiencies (PCEs), recently surpassing 15%. Despite rapid developments, achieving precise control over the morphologies of the perovskite films (minimizing pore formation) and enhanced stability and reproducibility of the devices remain challenging, both of which are necessary for further advancements. Here we demonstrate vacuum-assisted thermal annealing as an effective means for controlling the composition and morphology of the CH3NH3PbI3 films formed from the precursors of PbCl2 and CH3NH3I. We identify the critical role played by the byproduct of CH3NH3Cl on the formation and the photovoltaic performance of the perovskite film. By completely removing the byproduct through our vacuum-assisted thermal annealing approach, we are able to produce pure, pore-free planar CH3NH3PbI3 films with high PCE reaching 14.5% in solar cell device. Importantly, the removal of CH3NH3Cl significantly improves the device stability and reproducibility with a standard deviation of only 0.92% in PCE as well as strongly reducing the photocurrent hysteresis.

We have studied the photocatalytic activity of ZnO tetrapods, ZnO powder, and different ZnO nanoparticles. While nanoparticles with small particle size exhibited higher Brunauer–Emmett–Teller (BET) surface area, tetrapods exhibited significantly higher photocatalytic activity for degradation of different dyes. Degradation of four different dyes has been achieved for at least 5 times shorter time for tetrapods compared to nanoparticles (20 nm average particle size). Different ZnO samples have been characterized by variable-temperature photoluminescence and time-resolved photoluminescence measurements, and the relationship between optical properties, native defects, production of the reactive oxygen species, and photocatalytic dye degradation has been discussed.