Optimized phase separation in low-bandgap polymer:fullerene bulk heterojunction solar cells with criteria of solvent additives

Solvent Additives: Key Morphology‐Directing Agents for Solution‐Processed Organic Solar Cells

“…The diversity of chemical structures and behaviors within the growing catalog of successful solvent additives makes classification challenging. Solvent additives are often simply classified into nonconjugated or aromatic structures since examples from each category tend to have the same effects on a given system . Nonconjugated solvent additives, such as ODT and DIO, tend to increase crystallinity, possibly due to increased affinity for the alkyl side chains; aromatic solvent additives, such as 1CN and DPE, have higher affinity for the conjugated backbones of OSC materials, tending to increase their miscibility with fullerene .…”

In-Operando Study of the Effects of Solvent Additives on the Stability of Organic Solar Cells Based on PTB7-Th:PC71BM

“…11,24−26 In previous studies, the additives were classified as either non-aromatic or aromatic. 11 Both types of solvent additives need to fulfill two features. (1) Their boiling point (bp) must be much higher than that of the host solvent, and (2) one component of the blend must be more soluble in the additive than the other.…”

“…27−29 Because of its high bp of 332.5 °C and selective solubility for fullerenes, a highly phase-separated morphology can be developed to balance charge carrier mobilities and reduce charge recombination in bulk heterojunction (BHJ) solar cells. 11,30 Recently, o-chlorobenzaldehyde (CBA) with a bp of 212 °C has been used as an aromatic additive, which is beneficial for 200−300 nm thick active layers to form nanoscale morphologies. 31 Aside from optimizing the initial PCE of solar cells, their long-term stability is considered as a key for a successful real-world use of organic solar cells (OSCs).…”

“…Organic photovoltaics show great potential as a cost-effective alternative to conventional solar cells, due to their scalability and solution-based manufacturability. , The power conversion efficiencies (PCEs) of lab-scale devices have already exceeded 14%. − Because further increases in efficiency are always desirable in terms of economic viability, much effort has been devoted to optimizing the device morphology, which plays the most important role in attaining high efficiencies. − An ideal nanostructure of interpenetrating p- and n-type domains within a scale of 10–20 nm is critically important for efficient charge carrier separation and transport. − …”

“…To achieve a favorable morphology, various approaches, , such as thermal annealing, − solvent annealing, , and the use of solvent additives, have been studied. − Among those, solvent additives have been identified as the most effective way to control the morphology with respect to large-scale fabrication. ,− In previous studies, the additives were classified as either non-aromatic or aromatic . Both types of solvent additives need to fulfill two features.…”