RESUMEN
The development of ambient-air-processable organic-inorganic halide perovskite solar cells (OIHPSCs) is a challenge necessary for the transfer of laboratory-scale technology to large-scale and low-cost manufacturing of such devices. Different approaches like additives, antisolvents, composition engineering, and different deposition techniques have been employed to improve the morphology of the perovskite films. Additives that can form Lewis acid-base adducts are known to minimize extrinsic impacts that trigger defects in ambient air. In this work, we used the 3-thiophenemalonic acid (3-TMA) additive, which possesses thiol and carboxyl functional groups, to convert PbI2, PbCl2, and CH3NH3I to CH3NH3PbI3 completely. This strategy is effective in regulating the kinetics of crystallization and improving the crystallinity of the light-absorbing layer under high relative humidity (RH) conditions (30-50%). As a result, the 3-TMA additive increases the yield of the power conversion efficiency (PCE) from 14.9 to 16.5% and its stability under the maximum power point. Finally, we found that the results of this work are highly relevant and provide additional inputs to the ongoing research progress related to additive engineering as one of the efficient strategies to reduce parasitic recombination and enhance the stability of inverted OIHPSCs in ambient environment processing.
RESUMEN
Incorporating large organic cations to form 2D and mixed 2D/3D structures significantly increases the stability of perovskite solar cells. However, due to their low electron mobility, aligning the organic sheets to ensure unimpeded charge transport is critical to rival the high performances of pure 3D systems. While additives such as methylammonium chloride (MACl) can enable this preferential orientation, so far, no complete description exists explaining how they influence the nucleation process to grow highly aligned crystals. Here, by investigating the initial stages of the crystallization, as well as partially and fully formed perovskites grown using MACl, the origins underlying this favorable alignment are inferred. This mechanism is studied by employing 3-fluorobenzylammonium in quasi-2D perovskite solar cells. Upon assisting the crystallization with MACl, films with a degree of preferential orientation of 94%, capable of withstanding moisture levels of 97% relative humidity for 10 h without significant changes in the crystal structure are achieved. Finally, by combining macroscopic, microscopic, and spectroscopic studies, the nucleation process leading to highly oriented perovskite films is elucidated. Understanding this mechanism will aid in the rational design of future additives to achieve more defect tolerant and stable perovskite optoelectronics.
RESUMEN
Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280-320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320-400 nm) to UVC (<280 nm).
