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Kim, Taesu,Younts, Robert,Lee, Wonho,Lee, Seungjin,Gundogdu, Kenan,Kim, Bumjoon J. Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.42
<P>The photodegeneration of polymer solar cells (PSCs) based on polymer donors and fullerene acceptors limits their lifetime and reliability. Here, we demonstrate that replacing fullerene acceptors with naphthalenediimide (NDI)-based n-type polymers can significantly enhance the photo-stability of PSCs. As a model system, we compared the photo-stabilities of all-polymer solar cells (all-PSCs) and fullerene-based PSCs (fullerene-PSCs) using the same polymer donor (PBDTTTPD) exposed to one sunlight illumination. We observed a remarkable contrast in their photo-stabilities. After 4 days of irradiation, the performance of the fullerene-PSCs dropped by 50%, whereas the performance of the all-PSCs remained stable. The detailed analysis of charge dynamics measured by femtosecond transient absorption spectroscopy and space charge limited current measurements shows significant reduction in interfacial charge transfer and charge carrier mobility, which correlates with the loss in<I>J</I>SCand FF of the fullerene-PSCs under solar illumination. By contrast, for the all-PSCs, the ultrafast dynamics and charge mobility remained consistent after illumination. The NDI-based copolymer had high stability under light exposure, whereas the photo-induced dimerization of phenyl-C61-butyric acid methyl ester (PCBM) acceptors was responsible for the photo-degradation of fullerene-PSCs.</P>
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>
김선하,김영권,( Mohammad Afsar Uddin ),( Robert Younts ),이원호,( Bhoj Gautam ),최준형,( Cheng Wang ),( Kenan Gundogdu ),김범준,우한영 한국공업화학회 2016 한국공업화학회 연구논문 초록집 Vol.2016 No.1
Tuning the chemical structures of conjugated polymers by fluorination is a simple, yet powerful strategy for regulating their energy level and blend morphology between donor and acceptor. Herein, we investigate the effect of fluorination to P(NDI2OD-T2), the most generally used as acceptors in all-polymer solar cells (all-PSCs), on their photovoltaic properties. We developed all-PSCs based on PBDTTTPD as donor and P(NDI2OD-T2F) as acceptors, and examined their charge generation and recombination behaviors by TAS. These systems exhibit faster hole transports and longer polaron life time, and subsequently the high power conversion efficiency of 6.09%, compared with control devices using P(NDI2OD-T2) as acceptors (2.02%). Furthermore, higher miscibility of P(NDI2OD-T2F) with donors in blend films was also examined by AFM and R-SoXS. Therefore, we concluded that fluorination is effective strategy for high efficient all-PSCs due to deepening energy level and producing miscible morphology.