Jeongmo Kim

Ambipolar Triple Cation Perovskite Field Effect Transistors and Inverters

Ambipolar perovskite field-effect transistors and inverters with balanced mobilities are demonstrated. Thin-film field-effect-transistor-like inverters are developed, and a maximum gain of 23 in the first quadrant for VDD = 80 V is obtained.

Stable and null current hysteresis perovskite solar cells based nitrogen doped graphene oxide nanoribbons hole transport layer

Perovskite solar cells are becoming one of the leading technologies to reduce our dependency on traditional power sources. However, the frequently used component poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has several shortcomings, such as an easily corroded indium-tin-oxide (ITO) interface at elevated temperatures and induced electrical inhomogeneity. Herein, we propose solution-processed nitrogen-doped graphene oxide nanoribbons (NGONRs) as a hole transport layer (HTL) in perovskite solar cells, replacing the conducting polymer PEDOT:PSS. The conversion efficiency of NGONR-based perovskite solar cells has outperformed a control device constructed using PEDOT:PSS. Moreover, our proposed NGONR-based devices also demonstrate a negligible current hysteresis along with improved stability. This work provides an effective route for substituting PEDOT:PSS as the effective HTL.

New Horizons for Perovskite Solar Cells Employing DNA-CTMA as the Hole-Transporting Material.

We investigate solution-processed low-temperature lead-halide perovskite solar cells employing deoxyribose nucleic acid (DNA)-hexadecyl trimethyl ammonium chloride (CTMA) as the hole-transport layer and (6,6)-phenyl C61 -butyric acid methyl ester (PCBM) as electron-acceptor layer in an inverted p-i-n device configuration. The perovskite solar cells utilizing a bio-based charge-transport layer demonstrate power conversion efficiency values of 15.86 %, with short-circuit current density of 20.85 mA cm(-2) , open circuit voltage of 1.04 V, and fill factor of 73.15 %, and improved lifetime. DNA-based devices maintained above 85 % of the initial efficiency after 50 days in air.

Organic devices based on nickel nanowires transparent electrode

Herein, we demonstrate a facile approach to synthesize long nickel nanowires and discuss its suitability to replace our commonly used transparent electrode, indium-tin-oxide (ITO), by a hydrazine hydrate reduction method where nickel ions are reduced to nickel atoms in an alkaline solution. The highly purified nickel nanowires show high transparency within the visible region, although the sheet resistance is slightly larger compared to that of our frequently used transparent electrode, ITO. A comparison study on organic light emitting diodes and organic solar cells, using commercially available ITO, silver nanowires, and nickel nanowires, are also discussed.

Graphene oxide grafted polyethylenimine electron transport materials for highly efficient organic devices

We demonstrate that solution processed graphene oxide (GO) grafted polyethylenimine ethoxylate (PEIE) is an efficient electron transport layer for organic solar cells with an active layer that consists of poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) mixed with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The optimized GO:PEIE demonstrated the best efficiency of 8.21% compared to that of the GO and PEIE devices.

Bandgap tuning of mixed organic cation utilizing chemical vapor deposition process

Bandgap tuning of a mixed organic cation perovskite is demonstrated via chemical vapor deposition process. The optical and electrical properties of the mixed organic cation perovskite can be manipulated by varying the growth time. A slight shift of the absorption band to shorter wavelengths is demonstrated with increasing growth time, which results in the increment of the current density. Hence, based on the optimized growth time, our device exhibits an efficiency of 15.86% with negligible current hysteresis.

Zinc oxide nanorod doped graphene for high efficiency organic photovoltaic devices

We report the synthesis of zinc oxide nanorod (ZnR) doped graphene (G) for high performance organic photovoltaic (OPV) devices based on a low bandgap polymer, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) blended with a fullerene derivative (PC71BM). The use of ZnR–G in a PTB7:PC71BM-based inverted OPV device leads to substantial enhancement in device performance in contrast to the reference devices. The improved performance is attributed to the improved charge carrier separation and prolonged lifetime of the generated electron–hole pairs. In addition, we also found that extra pathways for the disappearance of the charge carriers exist due to the interactions between the excited ZnR and G, which shows that the ZnR–G have a lower recombination rate of electrons and holes under UV light illumination.