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Nam, Minwoo,Kim, Sungwoo,Kim, Sejin,Kim, Sang-Wook,Lee, Keekeun RSC Pub 2013 Nanoscale Vol.5 No.17
<P>We present hybrid solar cells with high efficiency utilizing a novel donor-acceptor combination of poly[2,6-(4,4'-bis-(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-alt-4,7(2,1,3-benzothiadiazole)] (PSBTBT) and a PbSxSe1-x inorganic semiconductor. Several nanocomposite parameters are evaluated in order to improve the hybrid device efficiency, including donor-acceptor materials, surface modification of the inorganic semiconductor, and mixture of quantum dots (QDs) and nanorods (NRs) in the polymer matrix. A high power conversion efficiency (PCE) of ~3.4% is attained from the optimal device with a PbS0.7Se0.3 QD?:?NR blending ratio of 0.3?:?0.7 (wt/wt) under air mass (AM) 1.5 solar illumination, which is attributed to the broad-range absorption of the solar energies and the efficient charge separation and transport dynamics. The optoelectronic and nanomorphological properties of these novel hybrid solar cells are described.</P>
Semi-transparent quaternary organic blends for advanced photovoltaic applications
Nam, Minwoo,Noh, Hye Yeon,Kang, Joo-Han,Cho, Junhee,Min, Byoung Koun,Shim, Jae Won,Ko, Doo-Hyun Elsevier 2019 Nano energy Vol.58 No.-
<P><B>Abstract</B></P> <P>In spite of enormous promise in a multitude of applications, semi-transparent organic photovoltaics (ST OPVs) relatively lag behind opaque OPVs in the efficiency, and further efforts are imperative to improve their performance while preserving their transparency and tunable color perceptivity. Here, we develop highly efficient ST OPVs based on quaternary blends (Q-blend) involving non-fullerene small molecules, and demonstrate their realistic application in four-terminal (4T) tandem PVs. The ST quaternary OPV (Q-OPV) exhibits superior power conversion efficiencies (PCEs) higher than those of the state-of-the-art ST OPVs under any irradiation conditions, while retaining high transparency and the possibility of implementing various colors. In particular, we achieve the first PCE value exceeding 15% (~15.46%) under indoor lighting among the ST OPVs reported to date. The 4T tandem configurations based on a ST Q-OPV with diverse opaque PVs demonstrate broadband photon harvesting, with aesthetic functions rendered from the color-codable ST Q-OPV. The benefits of the Q-blend platform, including efficient operation under any irradiation circumstance (both indoor and outdoor lighting) and device color codability via tuning the quaternary components, can further expand the applicability of the ST Q-OPV to various practical applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We demonstrate semi-transparent quaternary organic photovoltaics (ST Q-OPVs) for advanced photovoltaic applications. </LI> <LI> The ST Q-OPV is used in four-terminal tandem systems to accommodate an enhanced spectral response and aesthetic functions. </LI> <LI> The benefits of tunable color and efficient operation under any irradiation conditions expand the utility of the ST Q-OPV. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Ternary blend organic solar cells with improved morphological stability
Nam, Minwoo,Yoo, Jaehong,Park, Yunjae,Noh, Hye Yeon,Park, Yongkook,Cho, Junhee,Kim, Jung-A.,Kim, Jehan,Lee, Hyun Hwi,Chang, Rakwoo,Ko, Doo-Hyun The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.16
<P>Long-term stability of organic blends is a key factor for the practical use of organic solar cells (OSCs) in commercial fields. Here, we report the strategic incorporation of non-fullerene small molecules in polymer:fullerene blends to obtain ternary OSCs with improved efficiency and extended lifetimes. Non-fullerene small molecules employed in the polymer:fullerene blend successfully increased the photon-to-current conversion process as an efficient charge cascade acceptor. A combination of theoretical simulations and experimental measurements revealed that aggregation of meta-stable fullerene molecules was significantly alleviated in the ternary blend, thereby preventing an unintentional increase in the threshold for charge transfer during operation. Thus, the ternary OSCs could exhibit highly extended lifetimes with improved morphological stability and better resistance to performance decay under harsh real operational conditions compared to their binary counterparts. Combined with its high efficiency and improved device lifetimes, the high tolerance to the ternary blend thickness offers promise for commercially acceptable ternary OSCs fabricated by a printing process.</P>
A multifunctional fullerene interlayer in colloidal quantum dot-based hybrid solar cells
Nam, Minwoo,Park, Joongpill,Lee, Keekeun,Kim, Sang-Wook,Ko, Hyungduk,Han, Il Ki,Ko, Doo-Hyun The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.19
<P>Chemically modifying the surfaces of colloidal quantum dots (QDs) offers an effective approach to improve their photovoltaic performances. Ligand exchange processes, however, tend to cause nanoscale cracks throughout the QD-based films, which increases the leakage current and magnitude of recombination losses. Here, we have developed a multifunctional [6,6]-phenyl C61butyric acid methyl ester (PC60BM) cathode interlayer for use in polymer-QD hybrid bulk heterojunction (BHJ) solar cells. The PC60BM layer deposited onto the hybrid BHJ film<I>via</I>solution uniformly covered the nanocracks produced by QD surface ligand exchange with thiol and facilitated electron transport to the cathode. The PC60BM layer also improved photon harvesting at short wavelengths and formed an efficient vertical donor-acceptor/acceptor′ (D-A/A′) junction in the interfacial areas between the hybrid blend and PC60BM. The efficient vertical junction increased the probability of ultrafast exciton dissociation, provided pathways for effective transport and extraction of photo-generated electrons, and blocked holes to reduce recombination losses. These combined advantages significantly enhanced the overall efficiency of the hybrid solar cells over the current state-of-the-art efficiency.</P>
Nam, Minwoo,Lee, Jaejin,Lee, Kee-Keun Elsevier 2011 Microelectronic engineering Vol.88 No.8
<P><B>Abstract</B></P> <P>A novel dome-shaped and anti-reflective microdome array (MDA) was developed for a solar cell surface protection layer with the aim to improve the cell efficiency. Uniform microdomes in the array were obtained by isotropic wet-etching of quartz. The microdome patterns on the quartz plate were transferred to a polymer via 2 replica molding processes in order to fabricate a flexible MDA. When light passes through the developed microstructure array, the anti-reflective MDAs exhibited a higher transmittance and a lower reflectance when compared to their counterparts, bare planar layers. During the electrical testing of the GaAs solar cells under an illumination of air mass (A.M) 1.5, the cells covered by these MDAs showed a greatly increased current density (<I>J</I> <SUB>sc</SUB>) of up to 5.2%. The power conversion efficiency (PCE) was also remarkably increased up to 3.5%, when the MDA structure was utilized as the solar cell surface protection layer.</P>