Effects of Solvent Mixtures on the Nanoscale Phase Separation in Polymer Solar Cells

Abstract

The mixed solvent approach has been demonstrated as a promising method to modify nanomorphology in polymer solar cells. This work aims to understand the unique role of the additive in the mixture solvent and how the optimized nanoscale phase separation develops laterally and vertically during the non‐equilibrium spin‐coating process. We found the donor/acceptor components in the active layer can phase separate into an optimum morphology with the additive. Supported by AFM, TEM and XPS results, we proposed a model and identified relevant parameters for the additive such as solubility and vapor pressures. Other additives are discovered to show the ability to improve polymer solar cell performance as well.

Structure and morphology control in thin films of regioregular poly(3‐hexylthiophene)

“…However, the nanomorphology and the crystallinity of the films can be significantly modified by using high-boiling solvents, 49 solvent mixtures, or ''additives,'' that is, poor solvents such as 1,8-diiodooctane. [50][51][52] For instance, charge mobility is improved by a factor of 10 (>0.1 cm 2 V.s À1 ) when P3HT OFETs are prepared from 1,2,4-trichlorobenzene (TCB) rather than chloroform. 49 Thermal annealing further enhances charge transport by modifying the nanomorphology and crystallinity of the film.…”

Environmentally-friendly solvent processed fullerene-free organic solar cells enabled by screening halogen-free solvent additives

“…Though a large number of studies have been devoted to optimizing the fullerene-based blend morphologies during recent years, such as finding suitable solvent additives and screening the optimal solvent additive content [50][51][52], research of solvent additive utilization and efficiency is very limited for fullerene-free OSCs. For fullerene-free OSCs, the impact of solvent additives on the molecular packing of non-fullerene acceptors may differ from that of fullerene acceptors due to the totally different molecular conformation of the two.…”

Relation Between Nanomorphology and Performance of Polymer-Based Solar Cells

“…(Alargova et al, 2001) Solvents, distinctly dissolving one component of the blend, induce the aggregation of nanofibers and nanoparticles in the solvent prior to film deposition. (Yao et al, 2008) It was shown that (independent of the concentration of the additive) fullerene molecules crystallized into distributed aggregates in the presence of a "bad" solvent in the host solvent. Well aligned P3HT aggregates resulting in high degree of crystallinity due to the interchain π − π stacking were observed upon addition of hexane.…”