1‐Chloronaphthalene‐Induced Donor/Acceptor Vertical Distribution and Carrier Dynamics Changes in Nonfullerene Organic Solar Cells and the Governed Mechanism

Abstract

Electron donors and acceptors in organic solar cells (OSCs) shall strike a favorable vertical phase separation that acceptors and donors have sufficient contact and gradient accumulation near the cathodes and anodes, respectively. Random mixing of donors/acceptors at surface will result in charge accumulation and severe recombination for low carrier‐mobility organic materials. However, it is challenging to tune the vertical distribution in bulk‐heterojunction films as they are usually made from a well‐mixed donor/acceptor solution. Here, for the first time, it presents with solid evidence that the commonly used 1‐chloronaphthalene (CN) additive can tune the donor/acceptor vertical distribution and establish the mechanism. Different from the previous understanding that ascribed the efficiency enhancement brought by CN to the improved molecular stacking/crystallization, it is revealed that the induced vertical distribution is the dominant factor leading to the significantly increased performance. Importantly, the vertical distribution tunability is effective in various hot nonfullerene OSC systems and creates more channels for the collection of dissociated carriers at corresponding organic/electrode interfaces, which contributes the high efficiency of 18.29%. This study of the material vertical distribution and its correlation with molecular stacking offers methods for additives selection and provides insights for the understanding and construction of high‐performance OSCs.

Preferred Acceptor-Domain Positioning via a Phase-Switched Bulk Heterojunction for Self-Powered Photodetector and Photovoltaic Applications

“…As such, the morphology of the phase-switched BHJ in CN was exceptionally uniform due to the effect of the phase-switching mold, which minimized interfacial defects by enhancing adhesion even at the interface with the interlayer. In addition, when forming the BHJ via the phase-switching process, solvent penetration into the PEDOT:PSS layer was suppressed, thereby improving the chemical stability . The morphological stability was confirmed through the peak-to-valley change after 7 days.…”

“…In general, when forming the BHJ layer, most of the CB was volatilized first with the CN being volatilized later owing to the higher boiling point of the latter (263 °C) compared to the former (131.7 °C). Moreover, the arrangement of molecules due to the different solubility levels of the donors and acceptors is favorable for dissociating the generated charges. ,, Therefore, the synergistic effect between the phase-switched BHJ formation and the CN additive resulted in promoting the PCE by around 43% compared to the conventional device.…”

“…The surfaces of the conventional BHJ films in CB and CB–CN had similar root-mean-square (rms) values of 4.376 and 4.249 nm, respectively (Figure a,b, respectively). However, it can be seen that a larger domain formed in the BHJ with the CN additive due to the difference in the boiling points and miscibility of the CN additive and the host solvent: , the CN additive with a high boiling point has better miscibility with the smaller Y6 acceptor molecules than the larger PM6 molecules, which contributes to better molecular orientation and crystallization of Y6 in a vertically distributed form as the solvent evaporates. ,, However, the surface morphology of the phase-switched BHJ was changed; it became inverted by the addition of CN, resulting in a smoother surface with improved charge mobility and the suppression of internal defects. Hence, the rms value was significantly reduced to 0.998 nm, and in a peak-to-valley analysis, the Rpv value was dramatically reduced from 18.59 to 4.37 nm (Figure S8).…”

Morphology Evolution via a Generic Solvent Additive Concept Enables Large‐Area All‐Polymer Solar Cells with Negligible PCE Loss

“…A smaller 𝛿 difference indicated a better miscibility of these two materials. [54,55] Table 3 listed the detailed parameters, in which PTzBI (𝛿 = 19.96 MPa 1/2 ) and N2200 (𝛿 = 18.35 MPa 1/2 ) have similar 𝛿 value, indicating that the two materials have good miscibility. In this work, high-boiling DIO (168 °C) was used as solvent additive, and low-boiling 2-MeTHF (80 °C) was used as processing solvent.…”

Recent Advances of Solid Additives Used in Organic Solar Cells: Toward Efficient and Stable Solar Cells

“…In the past decade, many methods optimizing the morphology of the active layer have been developed. At present, the universal methods mainly include thermal annealing (TA), − solvent vapor annealing (SVA), − solution state, − and adding solvent additives. − TA is a widely employed method to induce the crystallization and phase separation of active layers in OPVs . During TA, active layers are heated at temperatures above their glass transition temperatures for some time period, usually dozens of seconds to minutes .…”