Miscibility Tuning for Optimizing Phase Separation and Vertical Distribution toward Highly Efficient Organic Solar Cells

Abstract

Blending multidonor or multiacceptor organic materials as ternary devices has been recognized as an efficient and potential method to improve the power conversion efficiency of bulk heterojunction devices or single‐junction components in tandem design. In this work, a highly crystalline molecule, DRCN5T, is involved into a PTB7‐Th:PC 70 BM system to fabricate large‐area organic solar cells (OSCs) whose blend film thickness is up to 270 nm, achieving an impressive performance of 11.1%. The significant improvement of OSCs after adding DRCN5T is due to the formation of an interconnected fibrous network with decreased π–π stacking and enhanced domain purity, in addition to the optimized vertical distribution of PTB7‐Th and PC 70 BM, producing more effective charge separation, transport, and collection. The optimized morphology and performance are actually determined by the miscibility in different components, which can be quantitatively described by the Flory–Huggins interaction parameter of −0.80 and 2.94 in DRCN5T:PTB7‐Th and DRCN5T:PC 70 BM blends, respectively. The findings in this work can potentially guide the selection of an appropriate third additive for high‐performance OSCs for the sake of large‐area printing and roll‐to‐roll fabrication from the view of miscibility.

Revealing Morphology Evolution in Highly Efficient Bulk Heterojunction and Pseudo‐Planar Heterojunction Solar Cells by Additives Treatment

“…The light intensity ( P light ) dependence of J SC reflects the extent of exciton recombination in devices. [ 61 ] The correspondent relationship between J SC and P light is J SC ∝ P light α , where α is the exponential factor. When the α is close to 1.00, implying that bimolecular recombination in the devices is weaker and can be ignored.…”

Vertical Miscibility of Bulk Heterojunction Films Contributes to High Photovoltaic Performance

“…Water contact angles (WCA) are considered as an effective method to reflect the miscibility between components. [ 36 ] WCA were performed to study surface energy of the films (Figure S6, Supporting Information). The surface free energy of PM6 is estimated to be 22.43 mN m −1 , which is lower than that of Y6(25.39 mN m −1 ), PC 71 BM(67.46 mN m −1 ).…”

High‐Performance Pseudoplanar Heterojunction Ternary Organic Solar Cells with Nonfullerene Alloyed Acceptor

“…However, such a method is unable to separate the donors and the acceptors, the vertical phase separation of the active layers are still not well regulated. There are also related literature reporting the use of orthogonal solvents or simultaneously citing a third solvent to increase the donor and the acceptor contact areas, and achieve higher efficiency whereas the choice of orthogonal solvents and device preparation process are more complicated 31–35. By summarizing the advantages and disadvantages of the above literature, we can find that when donor and acceptor materials were dissolved using nonorthogonal solvents, the processing of the films were well completed which can also regulate vertical phase separation well 36.…”