Solar phase-separated polymer blends

The film formation in fhe spin-coating process for the polymer/fuller-ene blend system in the mixture solvent is a complex process because it is a nonequilibrium state that both thermodynamic and kinetic parameters can influence phase separation, and the system contains four components with dissimilar physical/chemical properties. We found the donor/acceptor components in the active layer can phase separate into an optimum morphology during the spin-coating process with the additive. Supported by AFM, TEM, and X-ray photoelectron spectroscopy (XPS) results, a model as well as a selection rule for the additive solvent, and identified relevant parameters for the additive are proposed. The model is further validated by discovering other two additives to show the ability to improve polymer solar cell performance as well. 

Intercalation of fullerenes between side chains mostly determines the optimum polymer fullerene blending ratios. These findings offer explanations why large-scale phase separation occurs in some polymer fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. High fullerene content is necessary to create the phase separation needed for efficient BHJ solar cells, which leads to optimum blend ratios near 1 3 to 1 4 polymenfullerene if intercalation occurs. If no intercalation occurs, an optimum near 1 1 is usually found. 

Mori D, Benten H, Kosaka J, Ohkita H, Ito S, Miyake K. Polymer/polymer blend solar cells with 2.0% efficiency developed by thermal purification of nanoscale-phase-separated morphology. ACS Appl Mater Interfaces 2011 3(8) 2924—2927. 

Polymer layers can exhibit significantly improved performances if they possess a multicomponent phase-separated morphology. Kietzke et al. [55] presented two approaches to control the dimensions of phase separation in thin polymer-blend layers based on polymer nanospheres prepared by the miniemulsion process. In the first approach, helerophase solid layers are prepared from an aqueous dispersion containing nanoparticles of two polymers, whereas in the second approach, both polymers are already contained in each individual nanoparticle. In both cases, the upper limit for the dimension of phase separation is determined by the size of the individual nanoparticles, which can be adjusted down to a few tens of nanometres. They also demonstrated that the efficiencies of solar cells using... 

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