Recent Progress in Fused-Ring Based Nonfullerene Acceptors for Polymer Solar Cells

Abstract

The progress of bulk-heterojunction (BHJ) polymer solar cells (PSCs) is closely related to the innovation of photoactive materials (donor and acceptor materials), interface engineering, and device optimization. Especially, the development of the photoactive materials dominates the research filed in the past decades. Photoactive materials are basically classified as p-type organic semiconductor donor (D) and an n-type organic semiconductor acceptor (A). In the past two decades, fullerene derivatives are the dominant acceptors for high efficiency PSCs. Nevertheless, the limited absorption and challenging structural tunability of fullerenes hinder further improve the efficiency of PSCs. Encouragingly, the recent progresses of fused-ring based A-D-A type nonfullerene acceptors exhibit great potential in enhancing the photovoltaic performance of devices, driving the power conversion efficiency to over 13%. Such kind of nonfullerene acceptors is usually based on indacenodithiophene (IDT) or its extending backbone core and end-caped with strong electron-withdrawing group. Owing to the strong push-pulling effects, the acceptors possess strong absorption in the visible-NIR region and low-lying HOMO (highest occupied molecular orbital) level, which can realize both high open-circuit voltage and short-circuit current density of the devices. Moreover, the photo-electronic and aggregative properties of the acceptors can be flexibly manipulated via structural design. Many strategies have been successfully employed to tune the energy levels, absorption features, and aggregation properties of the fused-ring based acceptors. In this review, we will summarize the recent progress in developing highly efficient fused-ring based nonfullerene acceptors. We will mainly focus our discussion on the correlating factors of molecular structures to their absorption, molecular energy levels, and photovoltaic performance. It is envisioned that an analysis of the relationship between molecular structures and photovoltaic properties would contribute to a better understanding of this kind of acceptors for high-efficiency PSCs.

Sulfur Position in Pyrene-Based PTTIs Plays a Key Role To Determine the Performance of Perovskite Solar Cells When PTTIs Were Employed as Electron Transport Layers

“…It is worth noting that a large number of previous research studies have demonstrated that the perpendicular tetraphenyl substituents on the IDT and their analogue units could effectively increase the steric hindrance, reduce the intermolecular interaction, and thus prevent the over-self-aggregation and large phase separation in the film, which will facilitate the transport and the separation of electrons. 40 Therefore, in this work, to increase the solubility, enhance the electron density of the donor pyrene part, and facilitate the molecular packing of these two ETL compounds, four alkoxy groups, which are perpendicular to the pyrene plane, were intentionally introduced on the 4,5,9,10-positions through one-step diazo reaction with pyrene-4,5,9,10-tetraone. Meanwhile, it has been reported that the sulfur atom could form interfacial S−I or S−Pb interaction to passivate the crystal surfaces of the perovskite and was beneficial for enhancing the performance of PSCs.…”

Silicon and oxygen synergistic effects for the discovery of new high-performance nonfullerene acceptors

“…The development of new n -type small-molecule semiconductor materials as electron acceptors in bulk heterojunction (BHJ) organic photovoltaics (OPVs) has progressed rapidly and attracted worldwide attention in recent years because of the advantages of these materials over typical fullerene derivatives in terms of structural flexibility and absorbent tunability, thermal/photochemical stability, solubility/processability and synthetic costs 48 – 52 . Among the reported nonfullerene acceptors, acceptor–donor–acceptor (A-D-A) nonfullerene acceptors based on ladder-type π-systems seem to be the most successful to date due to their high electron mobility, suitable electronic energy levels, low bandgap, broad and strong absorpiton 53 – 56 . The further development of a novel ladder-type backbone is the core to construct new A-D-A nonfullerene acceptors for overcoming the issues in OPVs.…”

Silicon and Oxygen Synergistic Effects for Discovery of New High-Performance Nonfullerene Acceptors

“…We then carried out the synthesis of the two SiO5T isomers by intramolecular C−H bond arylation cyclization, as shown in Figure 2 thermal/photochemical stability, solubility/processability and synthetic costs [48][49][50][51][52] . Among the reported nonfullerene acceptors, acceptor-donor-acceptor (A-D-A) nonfullerene acceptors based on the laddertype π-systems seem to be the most successful ones to date due to their high electron mobility, suitable electronic energy levels, low bandgap, broad and strong absorpiton [53][54][55][56] . The development of novel laddertype backbone is the core to construct new A-D-A nonfullerene acceptors for further improving the performance of OPVs.…”