Joo Young Shim

2,2-dimethyl-2H-benzimidazole based small molecules for organic solar cells

We report the small molecules utilizing new electron-deficient unit, 2,2-dimethyl-2H-benzimidazole (MBI) and phenanthro[9,10-c][1,2,5]thiadiazole (PT), for the photovoltaic application. Donor-acceptor-donor (D-A-D) types of conjugated small molecules containing benzo[1,2-b;3,4-b′]dithiophene (BDT) as electron rich unit and MBI and PT as electron deficient units (SM1 and SM2) were synthesized. D-A-D type of small molecules has the abilities of increasing intramolecular charge transfer (ICT) inducing long wavelength absorption and lowering the HOMO level for the improvement of open-circuit voltage (VOC). SM1 was synthesized by coupling BDT and PT units by Stille coupling reaction with Pd(0)-catalyst. By using same type of Pd(0)-catalized reaction, BDT unit and MBI unit linked with two thiophenes were coupled to provide SM2. The spectrum of SM2 in the solid thin film shows absorption band with maximum peak at 601 nm and the absorption onset at 756 nm, corresponding to band gap of 1.64 eV. The device comprising SM2 with PCBM (3:7) showed a VOC of 0.62 V, a JSC of 1.69 mA/cm2, and a fill factor (FF) of 0.27, giving a power conversion efficiency of 0.28%.

Synthesis and properties of low band gap polymers based on thienyl thienoindole as a new electron-rich unit for organic photovoltaics

A series of polymers based on 6-(2-thienyl)-4H-thieno[3,2-b]indole (TTI), a new electron-rich unit for organic photovoltaics, was synthesized. By replacing the six-membered benzene ring of the carbazole with an electron-rich five-membered thiophene ring, an enhanced ICT effect between the electron-rich group and the electron-deficient group is expected to result in improved π-electron delocalization, low band gap and increased light-harvesting ability of the OPVs. The TTI unit, with a fused rigid backbone, has an efficient structure for the ICT effect and for tuning of the HOMO and LUMO energy levels to generate a low band gap. As electron-deficient units, 4,7-bis(4-hexylthiophen-2-yl)-2,1,3-benzothiadiazole (DTBT-h), 2-dimethyl-4,7-di(2-thienyl)-2H-benzimidazole (DTMBI) and 3,6-di(2-thienyl)-2,5 dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP) were introduced by using Stille polymerization. PTTIDTMBI and PTTIDPP have low band gaps and show absorption up to 849 and 948 nm, respectively. The highest PCE was achieved with the device fabricated from a PTTIDTBT-h : PC71BM (1 : 3 w/w) blend with 1,8-octanedithiol (ODT) as an additive. The device demonstrated a Voc value of 0.81 V, a Jsc value of 8.19 mA cm−2, and an FF of 0.51, giving a highest power conversion efficiency of 3.35%.

Organic Synthesis and Characteristics of Novel Conjugated Polymers with Cyano Group and Carbazole Unit for AMOLEDs

The present investigation deals with the synthesis, characterization and EL of new copolymers, CzCNPFV1, CzCNPFV2 and CzCNPFV3 by Knoevenagel condensation reaction. The CzCNPFVs was synthesized for promoted efficiency of reported CNPFV. The PL emission spectra of the CzCNPFVs in chloroform solution show maximum peaks at 476 ~ 479 nm. In thin films, maximum peaks of the CzCNPFVs appeared at 501 ~ 504 nm, red-shifted around 25 nm as compared to that in solution. The more negative energy of the LUMO of CzCNPFV1 or CzCNPFV2 indicates the electron injection process is easier than in CNPFV. From this result, higher quantum efficiency of CzCNPFV1 or CzCNPFV2 as compared to that of CNPFV can be expected due to its improved electron injection ability from the cathode.

Natural Frequency Extraction From Multiple Frequency Response Sample Sets Using the Fitting Error

We propose a method for selecting the most accurate natural frequency set from all of the natural frequency sets extracted from multiple frequency response sample sets. The accuracy of the natural frequency set is estimated from the proposed fitting error. The method is applied to synthetic data, the Method of Moments (MM) data and measured data, and variations of the error of the natural frequencies and the fitting error show an agreement.

Increased efficient copolymers with PFV and PPDFV for light emitting diodes

New electroluminescent copolymers with fluoro groups in vinylene unit, poly(9,9-di-hexylfluorene-2, 7-vinylene-co-pphenylenedifluorovinylene) (PFVPDFV), have been synthesized by the GILCH polymerization. The fluoro groups were introduced on vinylene units to increase the electron affinities of the copolymers. The PFVPDFVs exhibit absorption spectra with maximum peaks at 371 ~ 413 nm. In the PL spectra of PFVPDFVs, as the PDFV content increases up to 50% in the copolymer system, fwhm was decreased by 4 - 38 nm as compared to PFV. The HOMO energy levels of the copolymers were about 5.25 - 5.50 eV, and the LUMO energy levels were about 2.67-2.97 eV. The polymer LEDs (ITO/PEDOT/polymer/Al) of PFVPDFVs showed emission with maximum peaks at around 472 - 538 nm. By adjusting the feed ratios of PDFV in the copolymers, it was possible to tune the emission colors from greenish yellow to orange depending on the obtained CIE coordinates. The luminescence efficiencies of the copolymers at room temperature are about 0.1-1.47 cd/A. The introduction of up to 50 % of PDFV in PFVPDFVS can enhance the device performance to result in high current density, brightness and efficiency due to the increased electron injection ability caused by the presence of fluoro groups in the vinylene units.