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( Mohammad Afsar Uddin ),우한영 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1
The molecular weight of a conjugated polymer is one of the key factors for electronics device properties. In this study, a series of semi-crystalline PTTBT and PPDT2FBT polymers with different number-average molecular weights (Mn) were synthesized and their photovoltaic properties as electron donors for Polymer-PCBM and all-polymer solar cells (all- PSCs) were studied respectively. Tuning the Mn induced dramatic effects on the aggregation behaviors of the polymers and their bulk heterojunction (BHJ) morphology, which was thoroughly examined by GIWAX, Ro-SoXS, AFM etc. High Mn PPDT2FBT promoted a strong “face-on” geometry in the blend film, suppressed the formation of an excessively large crystalline domain, and facilitated molecularly-intermixed phases with acceptor material leading to high power conversion efficiency.
Mohammad Afsar Uddin,김태효,염승집,최효성,황승구,김진영,우한영 한국물리학회 2015 Current Applied Physics Vol.15 No.5
Three kinds of donoreacceptor (DeA) type photovoltaic polymers were synthesized based on 2,7- carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be -5.72, -5.67 and -5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[ 6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (VOC) in the range, 0.86e0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high VOC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (JSC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC71BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electronehole recombination at the polymer/PC71BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC71BM. The PCBTTPD:PC71BM device showed the best PCE of 3.42% with a VOC and JSC of 0.86 V and 7.79 mA cm-2, respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high VOC and sufficient energy offset for ensuring efficient hole transfer from PC71BM to the polymer.
Uddin, Mohammad Afsar,Kim, Youngkwon,Younts, Robert,Lee, Wonho,Gautam, Bhoj,Choi, Joonhyeong,Wang, Cheng,Gundogdu, Kenan,Kim, Bumjoon J.,Woo, Han Young American Chemical Society 2016 Macromolecules Vol.49 No.17
<P>We investigate the photovoltaic properties and charge dynamics of all polymer solar cells (all-PSCs) based on poly[(N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5'-(2,2'-bithiophene)] (P-(NDI2OD-T2)) and its fluorinated analogue, poly[(N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5'-(3,3'-difluoro-2,2'-bithiophene)] (P-(NDI2OD-T2F)), as the acceptor polymer and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-alt-5-octyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione] (PBDTTTPD) as the donor polymer. The PBDTTTPD:P(NDI2OD-T2)-based device has a high open-circuit voltage (V-OC) of 1.03 V but suffers from low power conversion efficiency (PCE) of 2.02% with a short-circuit current density (J(SC)) and fill factor (FF) of 4.45 mA cm(2) and 0.44, respectively. In a stark contrast, the PCE of PBDTTTPD:P(NDI2OD-T2F)-based PSC dramatically increases to 6.09% (V-OC = 1.00 V, J(SC) = 11.68 mA cm(2), and FF = 0.52). These results are attributed to the fluorination, which removes the energetic barrier for hole transfer and promotes the formation of the donor/acceptor blend morphology with suppressed phase separation and enhanced intermixed phases. The detailed charge dynamics examined by femtosecond transient absorption spectroscopy suggests the significantly increased hole transfer efficiency and larger populations of long-lived polarons for PBDTTTPD:P(NDI2OD-T2F).</P>
Uddin, Mohammad Afsar,Lee, Tack Ho,Xu, Shuhao,Park, Song Yi,Kim, Taehyo,Song, Seyeong,Nguyen, Thanh Luan,Ko, Seo-jin,Hwang, Sungu,Kim, Jin Young,Woo, Han Young American Chemical Society 2015 Chemistry of materials Vol.27 No.17
<P>Four different kinds of photovoltaic polymers were synthesized by controlling the intrachain noncovalent coulomb interactions through the incorporation of alkoxy- or alkylthio-substituted phenylene, 4,7-di(furan-2-yl)benzothiadiazole, and 4,7-di(thiophen-2-yl)benzothiadiazole as a building block. Fine modulation of the interplay of dipole–dipole, H-bond, and chalcogen–chalcogen interactions (O···S, O···H, S···S, S···F, etc.) along the polymeric backbone influenced the chain planarity, interchain organization, film morphology, and electrical and photovoltaic properties significantly. By replacing the alkoxy substituents with alkylthio groups, the torsional angle increased (136–168°) due to the absence of an O···S attractive coulomb interaction (and/or increased S···S steric hindrance), enhancing the amorphous nature with hindered interchain packing. The alkoxy-substituted polymers exhibited nanofibrillar structures, showing strong interlamellar scattering peaks up to (300) with tight face-on <I>π–π</I> stacking in grazing incidence X-ray scattering. The measured carrier mobility of the alkoxy-containing polymers was 1–2 orders of magnitude higher than that of the alkylthio-containing polymers. The incident-light-intensity-dependent photovoltaic characteristics clearly suggested efficient charge generation/extraction with less charge recombination for the alkoxy-containing semicrystalline polymers. The resulting photovoltaic energy conversion efficiency of the PPDT2FBT, PPDF2FBT, PPsDF2FBT, and PPsDT2FBT blended devices with PC<SUB>70</SUB>BM was measured to be 8.28%, 5.63%, 5.12%, and 0.55%, respectively. This study suggests an important molecular design guideline for the further optimization of photovoltaic polymers and devices by finely controlling the interplay of the weak noncovalent coulomb interactions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-17/acs.chemmater.5b02251/production/images/medium/cm-2015-02251p_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5b02251'>ACS Electronic Supporting Info</A></P>
Kang, Hyunbum,Uddin, Mohammad Afsar,Lee, Changyeon,Kim, Ki-Hyun,Nguyen, Thanh Luan,Lee, Wonho,Li, Yuxiang,Wang, Cheng,Woo, Han Young,Kim, Bumjoon J. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.6
<P>The molecular weight of a conjugated polymer is one of the key factors determining the electrical, morphological, and mechanical properties as well as its solubility in organic solvents and miscibility with other polymers. In this study, a series of semicrystalline poly[(2,5-bis(2-hexyldecyloxy)phenylene)-<I>alt</I>-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[<I>c</I>][1,2,5]thiadiazole)] (PPDT2FBT) polymers with different number-average molecular weights (<I>M</I><SUB>n</SUB>’s) (<B>PPDT2FBT</B><SUB><B>L</B></SUB>, <I>M</I><SUB>n</SUB> = 12 kg/mol; <B>PPDT2FBT</B><SUB><B>M</B></SUB>, <I>M</I><SUB>n</SUB>= 24 kg/mol; <B>PPDT2FBT</B><SUB><B>H</B></SUB>, <I>M</I><SUB>n</SUB>= 40 kg/mol) were synthesized, and their photovoltaic properties as electron donors for all-polymer solar cells (all-PSCs) with poly[[<I>N,N</I>′-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-<I>alt</I>-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)) acceptor were studied. The <I>M</I><SUB><I>n</I></SUB> effect of PPDT2FBT on the structural, morphological, electrical, and photovoltaic properties was systematically investigated. In particular, tuning the <I>M</I><SUB>n</SUB> induced dramatic effects on the aggregation behaviors of the polymers and their bulk heterojunction morphology of all-PSCs, which was thoroughly examined by grazing incident X-ray scattering, resonant soft X-ray scattering, and other microscopy measurements. High <I>M</I><SUB>n</SUB> <B>PPDT2FBT</B><SUB><B>H</B></SUB> promoted a strong “face-on” geometry in the blend film, suppressed the formation of an excessively large crystalline domain, and facilitated molecularly intermixed phases with P(NDI2OD-T2). Therefore, the optimized all-PSCs based on <B>PPDT2FBT</B><SUB><B>H</B></SUB><B>/</B>P(NDI2OD-T2) showed substantially higher hole and electron mobilities than those of <B>PPDT2FBT</B><SUB><B>L</B></SUB><B>/</B>P(NDI2OD-T2), leading to a power conversion efficiency exceeding 5%, which is one of the highest values for all-PSCs reported thus far.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-6/ja5123182/production/images/medium/ja-2014-123182_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5123182'>ACS Electronic Supporting Info</A></P>
Yang, Jie,Uddin, Mohammad Afsar,Tang, Yumin,Wang, Yulun,Wang, Yang,Su, Huimin,Gao, Rutian,Chen, Zhi-Kuan,Dai, Junfeng,Woo, Han Young,Guo, Xugang American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.27
<P>We present here a series of wide-band-gap (<I>E</I><SUB>g</SUB>: >1.8 eV) polymer donors by incorporating thiophene-flanked phenylene as an electron-donating unit and quinoxaline as an electron-accepting co-unit to attain large open-circuit voltages (<I>V</I><SUB>oc</SUB>s) and short-circuit currents (<I>J</I><SUB>sc</SUB>s) in nonfullerene organic solar cells (OSCs). Fluorination was utilized to fine-tailor the energetics of polymer frontier molecular orbitals (FMOs) by replacing a variable number of H atoms on the phenylene moiety with F. It was found that fluorination can effectively modulate the polymer backbone planarity through intramolecular noncovalent S···F and/or H···F interactions. Polymers (P2-P4) show an improved molecular packing with a favorable face-on orientation compared to their nonfluorinated analogue (P1), which is critical to charge carrier transport and collection. When mixed with IDIC, a nonfullerene acceptor, P3 with two F atoms, achieves a remarkable <I>V</I><SUB>oc</SUB> of 1.00 V and a large <I>J</I><SUB>sc</SUB> of 15.99 mA/cm<SUP>2</SUP>, simultaneously, yielding a power-conversion efficiency (PCE) of 9.7%. Notably, the 1.00 V <I>V</I><SUB>oc</SUB> is among the largest values in the IDIC-based OSCs, leading to a small energy loss (<I>E</I><SUB>loss</SUB>: 0.62 eV) while maintaining a large PCE. The P3:IDIC blend shows an efficient exciton dissociation through hole transfer even under a small energy offset of 0.16 eV. Further fluorination leads to the polymer P4 with increased chain-twisting and mismatched FMO levels with IDIC, showing the lowest PCE of 2.93%. The results demonstrate that quinoxaline-based copolymers are promising donors for efficient OSCs and the fluorination needs to be fine-adjusted to optimize the interchain packing and physicochemical properties of polymers. Additionally, the structure-property correlations from this work provide useful insights for developing wide-band-gap polymers with low-lying highest occupied molecular orbitals to minimize <I>E</I><SUB>loss</SUB> and maximize <I>V</I><SUB>oc</SUB> in nonfullerene OSCs for efficient power conversion.</P> [FIG OMISSION]</BR>