Origin of the Additive‐Induced V_OC Change in Non‐Fullerene Organic Solar Cells

Abstract

Additives are often used to adjust the morphology of the active layer to improve the performance of organic solar cells (OSCs). Here, taking typical high‐efficiency non‐fullerene systems as examples, the effect of the additive on the device performance in non‐fullerene OSCs is systematically investigated. Surprisingly, an unpresented VOC change is observed in the opposite direction of the two typical systems (PM6:Y6 and PTB7‐Th: ITIC) appearing after the incorporation of the additive DIO, which can be affected by the morphological differences as indicated by the several morphological studies. The bewildering VOC change caused by the additive in different material systems is supposed to originate from the different energy level variations as verified by the energy level studies. Molecular dynamic (MD) and density functional theory (DFT) calculations are also included to get an insight into the dynamic of the additive‐induced morphological differences that are supposed to contribute to the energy level changes. Combining a series of morphological and energic studies as well as the theoretical calculations, the origin of unforeseeable VOC changes caused by additives in non‐fullerene OSCs is clarified, and provides in‐depth insights into the effects of additives on device performance.

Hybrid Dihalogenation on the End Group of Indacenodithieno[3,2-b]thiophene-Based Small-Molecule Acceptors Enables Efficient Polymer Solar Cells Processed from Nonhalogenated Solvents and Additives

“…Interestingly, one can find that there is an obvious difference in V oc s of IT-FBr -based PSCs using DIO and 2-MN as the additive. The impact of the additive on V oc of organic photovoltaic cells had also been observed in other previous reports, − which would be attributed to the additive-induced morphological, molecular aggregation, and electronic energy level (HOMO/LUMO) changes. Moreover, some studies demonstrate that the V oc of the BHJ device also is closely related to the dark current ( J so ). , Specifically, the V oc values of BHJ solar cells exhibit a strong inverse correlation with J so .…”

“…When additive DIO was replaced by 2-MN, the PM6: IT-FBr -based blend film becomes relatively rough with a higher RMS of 2.07 nm (Figure c), which is unfavorable for charge transport, thus leading to obviously inferior FF in the corresponding PSC (Table ). However, the increased roughness may imply the improvement of crystallinity of IT-FBr after using 2-MN as the additive (see Figure h) . This result should be beneficial to increase the energy of the charge transfer state after replacing DIO with 2-MN, thus contributing to the improved V oc of the PSCs (from 0.82 to 0.89 V). ,, In contrast, blend films based on nonhybrid dihalogenated IT-4Cl and IT-4F present slightly coarse surfaces with higher RMS roughnesses of 2.41 and 2.43 nm, as shown in Figure d,e, respectively.…”

“…However, the increased roughness may imply the improvement of crystallinity of IT-FBr after using 2-MN as the additive (see Figure 5h). 51 This result should be beneficial to increase the energy of the charge transfer state after replacing DIO with 2-MN, thus contributing to the improved V oc of the PSCs (from 0.82 to 0.89 V). 51,59,60 In contrast, blend films based on nonhybrid dihalogenated IT-4Cl and IT-4F present slightly coarse surfaces with higher RMS roughnesses of 2.41 and 2.43 nm, as shown in Figure 5d,e, respectively.…”

“…51 This result should be beneficial to increase the energy of the charge transfer state after replacing DIO with 2-MN, thus contributing to the improved V oc of the PSCs (from 0.82 to 0.89 V). 51,59,60 In contrast, blend films based on nonhybrid dihalogenated IT-4Cl and IT-4F present slightly coarse surfaces with higher RMS roughnesses of 2.41 and 2.43 nm, as shown in Figure 5d,e, respectively. The increased RMS should be owed to the enhanced crystallinity of IT-4Cl and IT-4F.…”

Efficient organic solar cells processed from a halogen-free solvent based on benzo[1,2-b:4,5-b′]difuran terpolymers

“…It is noted that the V oc in the PBDF4F:IT-4F(o-XY) device was also negatively affected by the large phase separation in the film besides the energy level difference. 47,48 The improved J sc and FF in PBDF4F-Th2:IT-4F(o-XY) and PBDF4F-Th5:IT-4F(o-XY) devices are due to the formation of a more favorable film morphology during the film deposition as a result of the improved solubilities of the terpolymers in the o-XY solvent. In addition, the devices of these three polymers processed from the chlorinated CB solvent were also fabricated for a more direct comparison with o-XY processed devices, and their J-V curves and device data are shown in Fig.…”