Solubility of [6,6]-Phenyl-C₆₁-butyric Acid Methyl Ester and Optimal Blending Ratio of Bulk Heterojunction Polymer Solar Cells

Abstract

The nanoscale mechanism determining the optimal electron donor/acceptor blending ratios is not yet clear. In this study, we used coarse-grained molecular simulations to simulate the thermal annealing process of poly-2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene (PBTTT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends to reveal the correlation between solubility of PCBM in electron donor materials and the optimal electron donor/acceptor blending ratio of the bulk heterojunction polymer solar cells. Substantial intercalation of PCBM into PBTTT is observed, and an interpenetrating network comprising two phasesPBTTT-plus-PCBM and pure PCBMis formed when the blending ratio is beyond 1:1. By comparing morphological properties of PBTTT:PCBM blends with those of the poly(3-hexylthiophene) (P3HT):PCBM blend, a blend which we investigated earlier, we reveal that, in addition to specific interfacial area and percolation probabilities, the solubility of PCBM in PBTTT also has significant effects in determining the optimal blending ratio. Due to PCBM intercalation into PBTTT, more PCBM must be inserted for the precipitation of pure PCBM domains for electron transport. Herein, we provide insight into the effects of PCBM solubility and the nanoscale mechanisms determining the optimal blending ratios and demonstrate how multiscale simulation can potentially aid the development of novel bulk heterojunction blends.

Dynamics, Miscibility, and Morphology in Polymer:Molecule Blends: The Impact of Chemical Functionality

“…[36][37] The P3HT:acene blends here at ~1:1 wt/wt ratio exhibit similarly high miscibility as those of P3HT:PCBM and PBTTT:PCBM at the same blend ratio. Given these similar miscibilities between the P3HT:acene blends and P3HT:PCBM, we expect that phase separation in the acene-blends will be led by crystallization (or the lack thereof) of P3HT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 24 and the acene molecules, as it is in PCBM-blends.…”

“…[35][36][37][38] These modeling advantages allow us to build structure-morphology relationships that are relevant to device properties, such as donor-acceptor morphology, miscibility, and interfacial area, and may inform future designs of donor/non-fullerene acceptor combinations. In our mapping scheme, see Figure 2, we choose to represent the P3HT monomer and acene molecule with the fewest CG particles possible while retaining the molecular shape and chemical nature of the materials.…”

Effect of polydispersity on the bulk‐heterojunction morphology of P3HT:PCBM solar cells

“…The simulated solvent evaporation procedure follows from the literature . Brief description of force field parameters is presented in Table and representative CGMD beads for P3HT, PCBM, and CB molecules are illustrated in Figure .…”

Electrode Materials, Thermal Annealing Sequences, and Lateral/Vertical Phase Separation of Polymer Solar Cells from Multiscale Molecular Simulations

“…The details of the fitting procedures can be found elsewhere. 24,32 The optimized potentials parameters are compiled in Table S1 of the Supporting Information. The fitted CG force field for PEDOT and PSS can successfully reproduce the structural properties computed from AMD simulations, see Figure S3 (intramolecular CG degrees of freedom) and Figure S4 (intermolecular CG degrees of freedom, RDFs) of the Supporting Information.…”