Polymer solar cells (PSCs) consisting of fullerene bis-adduct and poly(3-hexylthiophene) (P3HT) blends have shown higher efficiencies than P3HT:phenyl C(61)-butyric acid methyl ester (PCBM) devices, because of the high-lying lowest unoccupied molecular orbital (LUMO) level of the fullerene bis-adducts. In contrast, the use of fullerene bis-adducts in donor-acceptor (DA) copolymer systems typically causes a decrease in the device's performance due to the decreased short-circuit current (J(SC)) and the fill factor (FF). However, the reason for such poor performance in DA copolymer:fullerene bis-adduct blends is not fully understood. In this work, bulk-heterojunction (BHJ)-type PSCs composed of three different electron donors with four different electron acceptors were chosen and compared. The three electron donors were (1) poly[(4,8-bis-(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene)-2,6-diyl-alt-(5-octylthieno[3,4-c]pyrrole-4,6-dione)-1,3-diyl] (PBDTTPD), (2) poly[(4,8-bis-(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT-C), and (3) P3HT polymers. The four electron acceptors were (1) PCBM, (2) indene-C(60) monoadduct (ICMA), (3) indene-C(60) bis-adduct (ICBA), and (4) indene-C(60) tris-adduct (ICTA). To understand the difference in the performance of BHJ-type PSCs for the three different polymers in terms of the choice of fullerene acceptor, the structural, optical, and electrical properties of the blends were measured by the external quantum efficiency (EQE), photoluminescence, grazing incidence X-ray scattering, and transient absorption spectroscopy. We observed that while the molecular packing and optical properties cannot be the main reasons for the dramatic decrease in the PCE of the DA copolymers and ICBA, the value of the driving force for charge transfer (ΔG(CT)) is a key parameter for determining the change in J(SC) and device efficiency in the DA copolymer- and P3HT-based PSCs in terms of fullerene acceptor. The low EQE and J(SC) in PBDTTPD and PBDTTT-C blended with ICBA and ICTA were attributed to an insufficient ΔG(CT) due to the higher LUMO levels of the fullerene multiadducts. Quantitative information on the efficiency of the charge transfer was obtained by comparing the polaron yield, lifetime, and exciton dissociation probability in the DA copolymer:fullerene acceptor films.

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The purpose of this study is to analyze the current status of Korean Language Education at the Support Center for Foreign Workers(SCFW) and to suggest improvement plans. For this purpose, the realities of Korean language education curriculum, textbooks and teachers at SCFW are examined. Although Korean language education is one of major businesses of SCFW, they do not have the education infrastructure and education expertise, So educational improvements are urgently needed. This study suggests that a curriculum that reflects the specific needs of foreign workers should be developed first and textbooks should be developed accordingly. In addition, the direction of providing teacher education to train professional teachers was suggested. This study would be meaningful as a discussion to find an efficient Korean language education plan for foreign workers, which has not been studied much in the past.