Gang-Young Lee

Dopant-free polymeric hole transport materials for highly efficient and stable perovskite solar cells

We report a dopant-free polymeric hole transport material (HTM) that is based on benzo[1,2-b:4,5:b′]dithiophene and 2,1,3-benzothiadiazole, which results in highly efficient and stable perovskite solar cells (∼17.3% for over 1400 h at 75% humidity). The HTM comprises a random copolymer (RCP), which is characterized using UV-vis absorption spectroscopy, cyclic voltammetry, space-charge-limited current, and grazing-incidence wide-angle X-ray scattering. The RCP-based perovskite solar cell exhibits the highest efficiency (17.3%) in the absence of dopants [lithium bis(trifluoromethanesulfonyl)imide and tert-butylpyridine]. The observed efficiency is attributed to a deep HOMO energy level and high hole mobility. In addition, the long-term stability of the device is dramatically improved by avoiding deliquescent or hygroscopic dopants and by introducing a hydrophobic polymer layer. RCP devices maintain their initial efficiency for over 1400 h at 75% humidity, whereas devices made of HTMs with additives fail after 900 h.

High-Field-Effect Mobility of Low-Crystallinity Conjugated Polymers with Localized Aggregates.

Charge carriers typically move faster in crystalline regions than in amorphous regions in conjugated polymers because polymer chains adopt a regular arrangement resulting in a high degree of π-π stacking in crystalline regions. In contrast, the random polymer chain orientation in amorphous regions hinders connectivity between conjugated backbones; thus, it hinders charge carrier delocalization. Various studies have attempted to enhance charge carrier transport by increasing crystallinity. However, these approaches are inevitably limited by the semicrystalline nature of conjugated polymers. Moreover, high-crystallinity conjugated polymers have proven inadequate for soft electronics applications because of their poor mechanical resilience. Increasing the polymer chain connectivity by forming localized aggregates via π-orbital overlap among several conjugated backbones in amorphous regions provides a more effective approach to efficient charge carrier transport. A simple strategy relying on the density of random copolymer alkyl side chains was developed to generate these localized aggregates. In this strategy, steric hindrance caused by these side chains was modulated to change their density. Interestingly, a random polymer exhibiting low alkyl side chain density and crystallinity displayed greatly enhanced field-effect mobility (1.37 cm(2)/(V·s)) compared with highly crystalline poly(3-hexylthiophene).

A comparative study on the thermal- and microwave-assisted Stille coupling polymerization of a benzodithiophene-based donor–acceptor polymer (PTB7)

We report a comparative study on the thermal- and microwave-assisted Stille-coupling polymerization of a benzodithiophene-based donor–acceptor polymer (PTB7). For this study, we synthesized PTB7 polymers through Stille-coupling polymerization under microwave conditions (M-PTB7, Mn = 75 kg mol−1, and D = 2.2) as well as thermal conditions (T-PTB7, Mn = 31 kg mol−1, D = 2.1). Although the microwave-assisted method increases the molecular weight of PTB7 in a short time, the power conversion efficiency of M-PTB7 (2.8%) is lower than that of T-PTB7 (7.8%). The microwave-assisted method was found to generate more structural defects from homo-coupling side reactions, resulting in a decrease in JSC and FF values for M-PTB7. Our findings highlight the importance of controlling the generation of homocoupled units during the synthesis of PTB7 polymers for high-performance PSCs.

Amine-Functionalized Covalent Organic Framework for Efficient SO 2 Capture with High Reversibility

Removing sulfur dioxide (SO2) from exhaust flue gases of fossil fuel power plants is an important issue given the toxicity of SO2 and subsequent environmental problems. To address this issue, we successfully developed a new series of imide-linked covalent organic frameworks (COFs) that have high mesoporosity with large surface areas to support gas flowing through channels; furthermore, we incorporated 4-[(dimethylamino)methyl]aniline (DMMA) as the modulator to the imide-linked COF. We observed that the functionalized COFs serving as SO2 adsorbents exhibit outstanding molar SO2 sorption capacity, i.e., PI-COF-m10 record 6.30 mmol SO2 g−1 (40 wt%). To our knowledge, it is firstly reported COF as SO2 sorbent to date. We also observed that the adsorbed SO2 is completely desorbed in a short time period with remarkable reversibility. These results suggest that channel-wall functional engineering could be a facile and powerful strategy for developing mesoporous COFs for high-performance reproducible gas storage and separation.

Premise-part adaptation laws for adaptive fuzzy control and its application to vehicle speed control

In adaptive fuzzy control, approximation accuracy of the designed fuzzy system plays a key role in the overall system performance. Up to now, a linear parameterization method has been used to derive suitable adaptive laws, even in the adaptation of premise-part membership functions. However, the premise-part adaptation schemes with linear parameterization have some fundamental limitation due to the inadequacy of the gradient algorithm for general nonlinearly parameterized functions. In the paper, a new adaptive fuzzy control method with adaptation both of the premise-part and consequence-part membership functions is presented. The proposed adaptive fuzzy control scheme does not suffer from the problems appearing in conventional premise-part adaptation by using a nongradient strategy. The global stability as well as performance enhancement is given via simulations and application results of vehicle speed control.