All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers

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• 作者：Nanjia Zhou ; Alexander S. Dudnik ; Ting I. N. G. Li ; Eric F. Manley ; Thomas J. Aldrich ; Peijun Guo ; Hsueh-Chung Liao ; Zhihua Chen ; Lin X. Chen ; Robert P. H. Chang ; Antonio Facchetti ; Monica Olvera de la Cruz ; Tobin J. Marks
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：February 3, 2016
• 年：2016
• 卷：138
• 期：4
• 页码：1240-1251
• 全文大小：827K
• ISSN：1520-5126

文摘

The influence of the number-average molecular weight (M_n) on the blend film morphology and photovoltaic performance of all-polymer solar cells (APSCs) fabricated with the donor polymer poly[5-(2-hexyldodecyl)-1,3-thieno[3,4-c]pyrrole-4,6-dione-alt-5,5-(2,5-bis(3-dodecylthiophen-2-yl)thiophene)] (PTPD3T) and acceptor polymer 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); N2200) is systematically investigated. The M_n effect analysis of both PTPD3T and N2200 is enabled by implementing a polymerization strategy which produces conjugated polymers with tunable M_ns. Experimental and coarse-grain modeling results reveal that systematic M_n variation greatly influences both intrachain and interchain interactions and ultimately the degree of phase separation and morphology evolution. Specifically, increasing M_n for both polymers shrinks blend film domain sizes and enhances donor–acceptor polymer–polymer interfacial areas, affording increased short-circuit current densities (J_sc). However, the greater disorder and intermixed feature proliferation accompanying increasing M_n promotes charge carrier recombination, reducing cell fill factors (FF). The optimized photoactive layers exhibit well-balanced exciton dissociation and charge transport characteristics, ultimately providing solar cells with a 2-fold PCE enhancement versus devices with nonoptimal M_ns. Overall, it is shown that proper and precise tuning of both donor and acceptor polymer M_ns is critical for optimizing APSC performance. In contrast to reports where maximum power conversion efficiencies (PCEs) are achieved for the highest M_ns, the present two-dimensional M_n optimization matrix strategy locates a PCE “sweet spot” at intermediate M_ns of both donor and acceptor polymers. This study provides synthetic methodologies to predictably access conjugated polymers with desired M_n and highlights the importance of optimizing M_n for both polymer components to realize the full potential of APSC performance.