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Jang, Woongsik,Cheon, Hyungin,Park, Soyun,Cho, Jae Sang,Yi, Minji,Kwon, Soon-Ki,Kim, Yun-Hi,Wang, Dong Hwan Applied Science Publishers 2017 Dyes and pigments Vol.145 No.-
<P><B>Abstract</B></P> <P>We synthesized PP-TPD, based on a phenanthro[1,10,9,8-cdefg]carbazole unit as a donor and a thieno [3,4-c]pyrrole-4,6-dione (TPD) unit as an acceptor for efficient bulk heterojunction photovoltaic cells. The copolymer achieves a relatively low bandgap (1.6 eV) by its internal charge-transfer, which concurs with the results of density functional theory (DFT) calculation for the distribution of HOMO and LUMO levels. In addition, we fabricated the bulk-heterojunction (BHJ) photovoltaic cells as a function of the blend ratio of the donor (PP-TPD) and acceptor (PC<SUB>70</SUB>BM), and applied a solvent additive and an interlayer to the device, with the optimized ratio used in this study. To comprehend the relationships between the device performance and the synergetic effects of 1,8-diiodooctane (DIO) and titanium oxide (TiO<SUB>x</SUB>) within the PP-TPD: PC<SUB>70</SUB>BM blends, we investigated the hole mobility related to the charge carrier transport, the charge generation, and the charge transport resistance using space-charge limited current (SCLC) measurement, photocurrent analysis, and impedance spectroscopy, respectively. Especially, we implemented fluorescence imaging by Raman spectroscopy, which related to the charge generation and recombination dynamics within the surface of photoactive areas.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PP-TPD copolymer revealed well-distribution of HOMO/LUMO and band-gap of 1.6 eV. </LI> <LI> PP-TPD copolymer was designed to improve intermolecular interaction and carrier mobility. </LI> <LI> Interface engineering via additive and interlayer affects homogeneous thin film morphology. </LI> <LI> Enhanced electrical parameters of Voc, Jsc, and FF are analyzed by charge carrier dynamics. </LI> <LI> Fluorescence imaging was conducted for the study of charge generation and recombination. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Jang, Woongsik,Wang, Dong Hwan American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.44
<P>The stamping transfer process, which provides a precise patterning of the target material without the limitation of an underlying layer, has attracted significant attention for large-scale roll-to-roll fabrication. Despite the need to minimize the peeling energy, expressed as the sum of adhesion energies, for a simple transfer process, many studies have not considered this effect. In this study, we introduced a wetting coefficient related with adhesions between polymers for the transfer design of organic photosensitive materials. We observed a difference in adhesion between polymer blends depending on the surface energy of the mold. We designed high-surface-energy polyurethane acrylate to enable a residue-free transfer process. The transfer process significantly contributed to the device stability through changes in dark currents, photocurrents, responsivity, and detectivity over time, compared to spin coating. In particular, the detectivity was maintained over 95% after 360 h, and no burn-in loss of internal resistance was observed in the device with a transferred active layer. X-ray photoelectron spectroscopy showed that a large interfacial change between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-<I>b</I>:4,5-<I>b</I>′]dithiophene-2,6-diyl-<I>alt</I>-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-<I>b</I>]thiophene-4,6-diyl):[6,6] phenyl C<SUB>71</SUB> butyric acid methyl ester obtained through spin coating occurred owing to solution penetration, whereas the transfer process provided a constant interface owing to morphology stabilization. Therefore, the transfer process with optimized adhesion properties can improve the device operation durability without burn-in loss, enabling a cost-effective fabrication of organic optoelectronic devices.</P> [FIG OMISSION]</BR>