MA02.09.04 : Ternary Blend Strategy for Efficient and Stable Nonfullerene Organic Solar Cells

9:15 AM–9:30 AM Apr 6, 2018 (America - Denver)

PCC West, 100 Level, Room 102 BC

Xiaoyu Liu1 Jialin Wang1 Yani Chen1 Ziqi Liang1

1, Fudan University, Shanghai, , China

Nonfullerene acceptors have recently received increasing attention since the power conversion efficiencies (PCEs) of their organic solar cells (OSCs) approach and even exceed those of the fullerene counterparts. Besides developing a variety of fullerene-free acceptors, the concept of ternary blend OSCs by incorporation of a third component has demonstrated as an alternative yet promising approach to the enhancement of device performance. In this regard, we have recently employed such a ternary strategy for constructing efficient and stable nonfullerene based OSCs. We first applied the 1D/2A (i.e., one donor and two acceptors) strategy into binary PTB7–Th:PDI benchmark system, in which the planar PDI acceptors often suffer from their strong crystallization and hence large π-aggregation in solid state.[1] Another planar ITIC acceptor was thus introduced based on its weak crystallinity and near-infrared light absorption. By finely tuning the PDI/ITIC weight ratio, the influences of individual ITIC and PDI on the optical, electronic and morphological properties of the ternary blend were studied. The complementary optical absorption was found in all ternary blends compared to their binary counterparts. It was further revealed that ITIC played a critical role on largely suppressing the PDI aggregates, while PDI aided to form an interpenetrating network morphology to facilitate charge transport in the ternary blend. Consequently, when the PDI/ITIC ratio is 3:7 (w/w), the PTB7–Th:ITIC:PDI based inverted solar cells exhibited the highest PCE of 8.64% due to their favorable out-of-plane π−π stacking, finest phase-separation morphology, and highest charge mobility.
Subsequently, we turned to investigate 2D/1A (i.e., two donors and one acceptor) ternary nonfullerene system.[2] Two polymer donors of PTB7-Th and PffBT4T-2OD with complementary crystalline properties and similar optical absorption were utilized in ITIC-based OSCs. The crystalline polymer donor of PffBT4T−2OD, on the one hand, functioned as an effective morphology regulator for the benchmark blend of PTB7−Th and ITIC. On the other hand, it can afford additional charge transport paths and facilitate charge transfer owing to the formation of cascade energy level alignment between PTB7−Th and ITIC. As a result, the ternary blends exhibited bicontinuous interpenetrating network structures, which yielded appropriate phase separation, suppressed charge recombination and efficient carrier transport. The optimal devices fabricated without any solvent additive or post-annealing treatment delivered high PCEs of 8.22% and 7.57% in N2 and air, respectively.
[1] J. Wang, J. Peng, X. Liu, Z. Liang, ACS Appl. Mater. Interfaces 2017, 9, 20704−20710.
[2] X. Liu, J. Wang, J. Peng, Z. Liang, Macromolecules 2017, 50, 6954−6960.