Hyungsub Woo

Because of the facile formation of defects in organometal halide perovskites, the defect passivation has become an important prerequisite for the stable and efficient perovskite solar cell (PSC). Regarding that ionic defects of the perovskites play a significant role on the performance and stability of PSCs, we introduce lithium fluorides as effective passivators based on their strong ionic characteristics and small ionic radii. Both Li⁺ and F^– are observed to successfully incorporate within the perovskite layer, improving the device performances with the best efficiency over 20%, while the hysteresis effects are significantly reduced, confirming the passivation of perovskite defects. Moreover, LiF restrains both thermal degradation and photodegradation of PSCs, where over 90% of the initial efficiencies have been retained by LiF-incorporated devices for more than 1000 h under either 1 sun illumination or 85 °C thermal condition. As the trap density of states is analyzed before and after the thermal stress, not only the mitigation of electronic traps as fabricated but also the dramatic relaxation of traps during the postannealing step is observed with the LiF incorporation. From this work, LiF has shown its potential as a promising ionic passivator, and the phenomenal achievement of device stability by LiF provides a clear insight to overcome the stability issues of PSCs, a key to the commercialization of next-generation photovoltaics.

As opposed to nano‐Si anodes, Si‐microparticle (Si‐MP)‐based negative electrode is still in an immature stage due to the fragility of particles of which dimension is farther from the critical size of Si. In terms of binder chemistry, the established strategies for nano‐Si anode can be moderately transferred to designing functional binders for commercially available Si‐MP. However, only a few studies have reported acceptable electrochemical properties of Si‐MP in the level of designing novel‐binder systems. Herein, the ionically crosslinked polyacrylate (PANa_0.8Fe_y) inspired by metallo‐supramolecular polymers is introduced as a binder for Si‐MP anode. Although cracking of Si‐MP is inevitable during cycles, the electrode components can effectively be confined within the supramolecular network, which reversibly adjusts its architecture via iron (Fe³⁺)‐carboxylate coordination. With appropriate compositions, the incorporation of ferric ion to sodium polyacrylate allows the Si‐MP to exhibit an excellent round‐trip capacity of ∼1400 mAh g⁻¹ after 400 cycles. The resulting electrochemical performance is demonstrated by several correlated factors: (i) type of supramolecular interactions, (ii) effect of cations (Na⁺/Fe³⁺) on the conformation of polymer, and (iii) mechanical properties of the electrode.

Interfacial degradation in perovskite solar cells is a critical issue to obtain long-term stability for the future commercialization. Especially, perovskite and organic-based hole-transport layer (HTL) react easily while the device is in operating conditions (heat, light, and air). To prevent the degradation, inorganic-based CuSCN HTL has emerged as an alternative, yet the interfacial reactivity is still not clearly elucidated. Herein, Cu₂O and CuSCN are co-utilized as efficient and stable HTL. While the uniform film formation with high-mobility Cu₂O remains difficult, Cu₂O-CuSCN nanocomposite can be excellently synthesized as an effective HTL, exhibiting power conversion efficiency (PCE) of 19.2% and sustaining its PCE over 90% for 720 h under extreme condition (85°C/85% of relative humidity, encapsulated). Chemical distribution analyzed by secondary-ion mass spectroscopy (SIMS) suggests that Cu₂O nanoparticle layer is clearly protecting the interface between the perovskite and CuSCN. The optoelectronic properties of the nanocomposite HTL and the improved solar cell performance are correlated through the characterization of recombination rate, electronic trap distribution in the bandgap, and charge-extraction efficiencies.

Silicon has been considered as a promising anode material due to its high theoretical capacity (3579 mAh g⁻¹), however, it suffers from capacity degradation owing to the series of multiscale fractures in the electrode caused by the volume variation (≈300%) during phase transitions. The molecular/structural design of polymeric binders has been pivotal in overcoming the challenges to improve the integrity of Si anode via strong interactions between active materials and binders. In this respect, the covalently crosslinked polyacrylamide (PAM) network, which effectively maintains its mechanical strength and shape, is introduced as a novel binder system for Si active materials. Unlike the thermal crosslinking, the abundant polar‐functional groups, related to the strong interactions between Si and polymer, are not sacrificed in their network by virtue of the in situ polymerization. Through the PAM gel, the Si‐based electrode exhibits a superior capacity of ≈1526 mAh g⁻¹ at an optimized crosslinker concentration after 500 cycles. In addition, the effect of the chemical/mechanical properties of PAM gel on the electrochemical properties of Si is adequately elucidated. The results will provide meaningful insight regarding the design of novel binders, especially in the application of the covalently crosslinked structure to Si‐based electrodes.

The reduced graphene oxide (RGO)/carbon double-coated 3-D porous ZnO aggregates (RGO/C/ZnO) have been successfully synthesized as anode materials for Li-ion batteries with excellent cyclability and rate capability. The mesoporous ZnO aggregates prepared by a simple solvothermal method are sequentially modified through distinct carbon-based double coating. These novel architectures take unique advantages of mesopores acting as space to accommodate volume expansion during cycling, while the conformal carbon layer on each nanoparticle buffering volume changes, and conductive RGO sheets connect the aggregates to each other. Consequently, the RGO/C/ZnO exhibits superior electrochemical performance, including remarkably prolonged cycle life and excellent rate capability. Such improved performance of RGO/C/ZnO may be attributed to synergistic effects of both the 3-D porous nanostructures and RGO/C double coating.