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Lu, Chunyuan,Choi, In Taek,Kim, Jeongho,Kim, Hwan Kyu Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.38
<P>Perovskite solar cells (PrSCs) have emerged as a very promising technology in the field of photovoltaics by demonstrating power conversion efficiencies (PCEs) soaring from 3.9% to above 22% within the past eight years. To date, perovskite solar cells mainly depend on spiro-OMeTADto perform a key role as a hole transporting material (HTM). However, the complicated multi-step synthetic procedures and high-cost purification process for spiro-OMeTADlimited its potential for commercial application. Herein, three new carbazole-based HTMs with a starburst structure, coded asSGT-405(3,6),SGT-410(3,6) andSGT-411(3,6)<I>via</I>tuning the substitution position from the (2,7) to the (3,6) position of the carbazole moiety, have been successfully synthesized<I>via</I>three-step synthesis from commercially available reagents and investigated for highly efficient perovskite solar cells. By adopting this strategy, among them, molecularly engineered carbazole derivativeSGT-405(3,6) exhibits significantly increased<I>T</I>g(192.7 °C), improved film forming ability, reduced hole reorganization energy and enhanced hole mobility compared to its parent moleculeSGT-405(2,7) and spiro-OMeTAD. Owing to the promising properties ofSGT-405(3,6), meso-porous type PrSCs employingSGT-405(3,6) showed a remarkable PCE of 18.87%, which is better than that of the photovoltaic device employing spiro-OMeTAD(17.71%). To the best of our knowledge, the achieved PCE (18.87%) is the highest value reported for devices with the structure of FTO/compact TiO2/meso-porous TiO2/CH3NH3PbI3−xClx/HTM/Au employing small-molecular HTMs. Meanwhile, owing to the simple synthesis ofSGT-405(3,6), compared withSGT-405(2,7) previously developed by our group, synthesis cost was much lowered, resulting in low cost compared to the spiro-OMeTADandSGT-405(3,6), by approximately three times. Furthermore, the long-term device stability of PrSCs was enhanced forSGT-405(3,6) to some extent compared to those of other HTMs studied here due to the good uniform capping layer ofSGT-405(3,6) on top of the perovskite layer and the prevention of moisture penetration into the perovskite layer. Therefore,SGT-405(3,6) is a promising low-cost and efficient non-spiro type HTM with potential to replace expensive spiro-OMeTADfor PrSCs.</P>
Lu, Chunyuan,Dong, Qi,Tulugan, Kelimu,Park, Yeong Min,More, Mahendra A.,Kim, Jaeho,Kim, Tae Gyu American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.2
<P>In this research, catalyst-free vertically aligned boron doped carbon nanowalls films were fabricated on silicon (100) substrates by MPECVD using feeding gases CH4, H-2 and B2H6 (diluted with H-2 to 5% vol) as precursors. The substrates were pre-seeded with nanodiamond colloid. The fabricated CNWs films were characterized by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. The data obtained from SEM confirms that the CNWs films have different density and wall thickness. From Raman spectrum, a G peak around 1588 cm(-1) and a D band peak at 1362 cm(-1) were observed, which indicates a successful fabrication of CNWs films. The EDX spectrum of boron doped CNWs film shows the existence of boron and carbon. Furthermore, field emission properties of boron doped carbon nanowalls films were measured and field enhancement factor was calculated using Fowler-Nordheim plot. The result indicates that boron doped CNWs films could be potential electron emitting materials.</P>
Lu, Chunyuan,Paramasivam, Mahalingavelar,Park, Kyutai,Kim, Chul Hoon,Kim, Hwan Kyu American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.15
<P>Three phenothiazine-based A−π-D−π-D−π-A-type small molecules containing various terminal acceptor units, which act as Lewis base blocks, have been synthesized via an efficient and step-economical, direct C-H arylation strategy in the aim toward the development of hole-transporting materials (HTMs) with multifunctional features (such as efficient hole extraction layer, trap passivation layer, and hydrophobic protective layer) for perovskite solar cells (PrSCs). Optical-electrochemical correlation and density functional theory studies reveal that dicyanovinylene acceptor in <B>SGT-421</B> downshifted the highest occupied molecular orbital (HOMO) level (−5.41 eV), which is more proximal to the valence band (−5.43 eV) of the perovskite, whereas <I>N</I>-methyl rhodanine in <B>SGT-420</B> and 1,3-indanedione (IND) in <B>SGT-422</B> destabilized the HOMO, leading to an increased interfacial energy-level offset. <B>SGT-421</B> exhibits superior properties in terms of a sufficiently low-lying HOMO level and favorable energy-level alignment, intrinsic hole mobility, interfacial hole transfer, hydrophobicity, and trap passivation ability over <I>spiro</I>-<B>OMeTAD</B> as a benchmark small-molecule HTM. As envisaged in the design concept, <B>SGT-421</B>-based PrSC not only yields a comparable efficiency of 17.3% to the state-of-art of <I>spiro</I>-<B>OMeTAD</B> (18%), but also demonstrates the enhanced long-term stability compared to the <I>spiro</I>-<B>OMeTAD</B> because of its multifunctional features. More importantly, the synthetic cost of <B>SGT-421</B> is estimated to be 2.15 times lower than that of <I>spiro</I>-<B>OMeTAD</B>. The proposed design strategy and the study of acceptor-property relationship of HTMs would provide valuable insights into and guidelines for the development of new low-cost and efficient multifunctional HTMs toward the realization of efficient and long-term stable PrSCs.</P> [FIG OMISSION]</BR>
Dong, Qi,Lu, Chunyuan,Tulugan, Kelimu,Jin, Chunzi,Yoon, Soo Jong,Park, Yeong Min,Kim, Tae Gyu American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.2
<P>Multi wall carbon nanotubes (MWCNTs) and diamond are renowned as superlative material due to their relatively high thermal conductivity and hardness while comparing with any bulk materials. In this research, polyacrylonitrile (PAN) solution incorporated with MWCNTs at an alteration of mass fractions (0 wt%, 0.6 wt%, 1 wt%, 2 wt%) were fabricated via electrospinning under optimized parameters. Dried composite nanofibers were stabilized and carbonized, after which water base polytrafluorethylene (PTFE) mixed with nano diamond powder solution was spin coated on them. Scanning electron microscopy, Raman spectroscopy, X-ray scattering and Laserflash thermal conductivity were used to characterize the composite nanofiber sheets. The result shows that the thermal conductivity increased to 4.825 W/m K from 2.061 W/mK. The improvement of thermal conductivities is suggesting the incorporation of MWCNTs.</P>