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.

High performance all-small-molecule solar cells: engineering the nanomorphology via processing additives

“…5,6 Despite the success of fullerene acceptors, they still suffer from several limitations, which signicantly constrain the development of new donor materials; these include limited visible light absorption, synthetic difficulty in electronically modifying fullerenes, high costs of high purity materials, and frequently rather poor thermal stability of blends. 7,8 Therefore, recent research efforts have been devoted to exploring and understanding alternative acceptors via electron-decient subunits to replace fullerene derivatives. Considerable efforts were dedicated to developing nonfullerene acceptors (NFAs) such as conjugated polymer and small molecule acceptors, and the highest PCEs of over 10% were reported for non-fullerene polymer solar cells (PSCs) in single-junction devices.…”

A New Electron‐Rich Unit for Polymer Electron Acceptors: 4,4‐Difluoro‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene

“…[1][2][3] The development of polymer electron acceptors lags far behind that of polymer electron donors. [9][10][11][12][13][14][15][16][17][18][19][20] Both the Da nd Au nits are very important for photovoltaic performance of polymer electron acceptors.T he Du nit determines the crystallinity and electron mobility of polymer electron acceptors,a nd consequently affects the morphology of active layer and all-PSC devicep erformance. [9][10][11][12][13][14][15][16][17][18][19][20] Both the Da nd Au nits are very important for photovoltaic performance of polymer electron acceptors.T he Du nit determines the crystallinity and electron mobility of polymer electron acceptors,a nd consequently affects the morphology of active layer and all-PSC devicep erformance.…”

“…[9][10][11][12][13][14][15][16][17][18][19][20] Both the Da nd Au nits are very important for photovoltaic performance of polymer electron acceptors.T he Du nit determines the crystallinity and electron mobility of polymer electron acceptors,a nd consequently affects the morphology of active layer and all-PSC devicep erformance. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] In this manuscript, we report 4,4-difluoro-4H-cyclopenta[2,1-b:3,4-b']dithiophene (fCDT) as an ew electron-rich unit to design polymer electron acceptors( Figure 1a). [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] In this manuscript, we report 4,4-difluoro-4H-cyclopenta[2,1-b:3,4-b']dithio...…”

Thieno[3,4‐c]pyrrole‐4,6‐dione‐3,4‐difluorothiophene Polymer Acceptors for Efficient All‐Polymer Bulk Heterojunction Solar Cells

“…N bridged thienylthiazole, [10] and various nitrile-derived motifs, [1,11] with reported PCEs in range of 1-5 %. [16] Here,w en ote that at otal of six batches of the PTPD[2F]T(2HD) were prepared to demon-[*] Dr. [2,12] In this contribution, we report on as et of branched-alkyl-substitutedp olymer acceptors composed of thieno[3,4-c]pyrrole-4,6-dione (TPD) [13] and 3,4difluorothiophene ([2F]T) [14] motifs,a nd show that the appropriately functionalized all-thiophene analogue poly-(thieno[3,4-c]pyrrole-4,6-dione-alt-3,4-difluorothiophene), namely PTPD[2F]T (Figure 1a), can achieve PCEs of up to 4.4 %i nB HJ solar cells with PCE10 (poly[4,thiophen-2-yl)benzo [1,2-b;4,5-b']dithiophene-2,6diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2carboxylate-2-6-diyl)],a lso commonly referred to as PTB7-Th)a sthe polymer donor (model system;F igure 1b).…”

“…[6b,15] The PTPD[2F]T analogues were purified by established protocols: [13c] using the strongly complexing ligand N,N-diethyl-2phenyldiazenecarbothioamidetoremove palladium residues, and subjecting the polymers to Soxhlet extractions (methanol, dichloromethane) to remove short-chain oligomers,t hus affording batches of comparable number-average MW (16.2-18.6 kDa) and polydispersity indexes (PDI = 1.8-2.0; see Table S1 in the Supporting Information). [16] Here,w en ote that at otal of six batches of the PTPD[2F]T(2HD) were prepared to demon-strate batch-to-batch repeatability (see Table S1) and consistencya cross our device analyses. [16] Here,w en ote that at otal of six batches of the PTPD[2F]T(2HD) were prepared to demon-strate batch-to-batch repeatability (see Table S1) and consistencya cross our device analyses.…”