title: All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers.
abstract: The influence of the number-average molecular weight (Mn) 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 Mn effect analysis of both PTPD3T and N2200 is enabled by implementing a polymerization strategy which produces conjugated polymers with tunable Mns. Experimental and coarse-grain modeling results reveal that systematic Mn variation greatly influences both intrachain and interchain interactions and ultimately the degree of phase separation and morphology evolution. Specifically, increasing Mn for both polymers shrinks blend film domain sizes and enhances donor-acceptor polymer-polymer interfacial areas, affording increased short-circuit current densities (Jsc). However, the greater disorder and intermixed feature proliferation accompanying increasing Mn 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 Mns. Overall, it is shown that proper and precise tuning of both donor and acceptor polymer Mns is critical for optimizing APSC performance. In contrast to reports where maximum power conversion efficiencies (PCEs) are achieved for the highest Mns, the present two-dimensional Mn optimization matrix strategy locates a PCE "sweet spot" at intermediate Mns of both donor and acceptor polymers. This study provides synthetic methodologies to predictably access conjugated polymers with desired Mn and highlights the importance of optimizing Mn for both polymer components to realize the full potential of APSC performance.
authors.forename: Nanjia
authors.initials: N
authors.lastname: Zhou
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Dudnik
authors.forename: Ting I N G
authors.initials: TI
authors.lastname: Li
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
authors.forename: Eric F
authors.initials: EF
authors.lastname: Manley
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Aldrich
authors.forename: Peijun
authors.initials: P
authors.lastname: Guo
authors.forename: Hsueh-Chung
authors.initials: HC
authors.lastname: Liao
authors.affiliation: Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, United States.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
authors.forename: Lin X
authors.initials: LX
authors.lastname: Chen
authors.forename: Robert P H
authors.initials: RP
authors.lastname: Chang
authors.affiliation: Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, United States.
authors.forename: Antonio
authors.initials: A
authors.lastname: Facchetti
authors.forename: Monica
authors.initials: M
authors.lastname: Olvera de la Cruz
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks