Chia Ching Kee

Methylammonium lead iodide (MAPbI₃) is a benchmark absorber for low-cost, high-efficiency perovskite solar cells (PSCs), but its practical deployment is constrained by small grain sizes, high defect densities, and moisture-sensitive surfaces that limit both efficiency and stability. Here, we demonstrate that covalent organic frameworks (COFs) built from commercially available building blocks provide a powerful, multifunctional route to overcome these limitations by simultaneously regulating crystallization, passivating defects, and tuning surface properties in MAPbI₃ thin films. Three hydrazone-linked and β-ketoenamine frameworks, denoted DMTH-COF, Boc-PDA-COF and Tp-COF, were prepared by condensing 2,5-dimethoxyterephthalohydrazide (DMTH), Boc-PDA-phenylenediamine (Boc-PDA), and 1,3,5-triformylphloroglucinol (Tp), respectively, and were incorporated at low loading into the MAPbI₃ precursor solution. X-ray diffraction and FE-SEM reveal that all three additives preserve the tetragonal perovskite phase while enlarging the grain size from a few hundred nanometers in pristine films to about 1 μm for DMTH-modified layers, accompanied by narrowed diffraction peaks and reduced microstrain. Raman and FTIR spectroscopy show COF-induced modifications of Pb–I and CH₃NH₃⁺ vibrational modes, indicating specific coordination and hydrogen-bonding interactions that stabilize the lattice and reduce trap density. UV-Vis spectra confirm strong visible-light absorption at an unchanged optical bandgap of 1.56 eV across all films, while steady-state PL and EQE measurements evidence enhanced radiative efficiency and improved photon-to-current conversion, particularly at longer wavelengths. X-ray photoelectron spectroscopy confirms that the framework is retained within the film after annealing, the modified absorber showing a N 1s component at 399.7 eV that is absent from the pristine reference, while the Pb 4f and I 3d core levels shift in parallel with their spin–orbit splittings preserved and no metallic lead detected. These material-level improvements translate into substantial device gains in n-i-p PSCs (FTO/c-TiO₂/m-TiO₂/COF:MAPbI₃/Spiro-OMeTAD/Au). Relative to pristine MAPbI₃ cells (PCE ≈ 14.7%), COF-modified devices exhibit higher Voc, Jsc, and FF, with DMTH-COF-modified cells achieving Voc = 1.183 V, Jsc = 22.98 mA cm⁻², FF = 76.46%, and PCE = 20.78%, alongside reduced series resistance, increased shunt resistance, and improved device-to-device reproducibility. Water-contact-angle and EDX analyses confirm that COF addition increases surface hydrophobicity and preserves near-ideal Pb:I stoichiometry, supporting enhanced environmental stability. This study introduces bulk COF doping as a simple, scalable strategy to engineer MAPbI₃ microstructure, energetics, and surface chemistry in a single processing step, and identifies DMTH-COF as the most effective of the three frameworks. More broadly, it positions COF–perovskite hybrids as a tunable platform for high-efficiency, durable perovskite optoelectronics.

This paper presents a finger-actuated micropump with a consistent flow rate and no backflow. The fluid dynamics in interstitial fluid (ISF) extraction microfluidics are studied through analytical, simulation, and experimental methods. Head losses, pressure drop, diodocity, hydrogel swelling, criteria for hydrogel absorption, and consistency flow rate are examined in order to access microfluidic performance. In terms of consistency, the experimental result revealed that after 20 s of duty cycles with full deformation on the flexible diaphragm, the output pressure became uniform and the flow rate remained at nearly constant levels of 2.2 μL/min. The flow rate discrepancy between the experimental and predicted flow rates is around 22%. In terms of diodicity, when the serpentine microchannel and hydrogel-assisted reservoir are added to the microfluidic system integration, the diodicity increases by 2% (Di = 1.48) and 34% (Di = 1.96), respectively, compared to when the Tesla integration (Di = 1.45) is used alone. A visual and experimentally weighted analysis finds no signs of backflow. These significant flow characteristics demonstrate their potential usage in many low-cost and portable microfluidic applications.