In general, mixed cations and anions containing formamidinium (FA), methylammonium (MA), caesium, iodine, and bromine ions are used to stabilize the black α-phase of the FA-based lead triiodide (FAPbI3) in perovskite solar cells. However, additives such as MA, caesium, and bromine widen its bandgap and reduce the thermal stability. We stabilized the α-FAPbI3 phase by doping with methylenediammonium dichloride (MDACl2) and achieved a certified short-circuit current density of between 26.1 and 26.7 milliamperes per square centimeter. With certified power conversion efficiencies (PCEs) of 23.7%, more than 90% of the initial efficiency was maintained after 600 hours of operation with maximum power point tracking under full sunlight illumination in ambient conditions including ultraviolet light. Unencapsulated devices retained more than 90% of their initial PCE even after annealing for 20 hours at 150°C in air and exhibited superior thermal and humidity stability over a control device in which FAPbI3 was stabilized by MAPbBr3.

This certifies that the thesis of Chang Ki Moon is approved.

For efficient electrochemical catalysts, several molecular-scale descriptors have been proposed for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Various descriptors of perovskite catalysts have been proposed successfully for understanding either ORR or OER, but previous studies are insufficient to explain and thus boost up both ORR and OER simultaneously due to obstacles such as many different chemical compositions, structures, and metal orbital bands. Therefore, we investigate ORR/OER activities as a function of only oxygen vacancy concentration in perovskite oxides of Sm 0.5 Sr 0.5 CoO 3−δ (SSC) to check the close relationship between delta (δ) and the electronic structure. Interestingly, the improved performance of both ORR and OER is explained by the change in the oxidation state of the transition metal caused by the increase in oxygen vacancies. Unfortunately, most previous research studies have focused on the effect of only oxygen vacancy (δ) on responsiveness. To confirm this, we performed density functional theory (DFT) analysis to find the more dominant factor on whether the activity descriptor is either δ or oxidation states of transition metals. The DFT analysis reveals that the ORR and OER activities of SSC are simultaneously improved by the reduced gap between d-and p-band centers (ΔE d−p ) caused by the raised d-band center (M d ). X-ray absorption spectroscopy has provided the exact electronic states of all the transition metals. Here, we report that an important factor of ORR/OER is affected only by the oxidation state of the transition metal in the perovskite oxide, not by the oxygen vacancy concentration.

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The facile tuning of the gate size and the chemical functionalization of zeolitic imidazolate framework-8 (ZIF-8) were achieved by the postsynthetic modification with 3-amino-1,2,4-triazole. The resulting amine functionalized ZIF-8 particles enabled CO2 selective adsorption and further chemical modifications.