Y-serious acceptors and the multi-components strategy, the power conversion efficiencies (PCEs) of the single-junction OPVs have already reached 19%, [19,20] with the best fill factors (FFs) exceeding 80%. [21,22] However, the trade-off between the open-circuit voltage (V oc ) and the short-circuit current density (J sc ) still remains as a challenge to handle with in OPV devices. [23][24][25][26][27] Therefore, the synergistic improvement of V oc and J sc will be attractive for marching the efficiencies further for OPVs. [28][29][30] The charge transfer (CT) state cannot only affect the energy loss (E loss ) but also the generation efficiency of photo-induced carriers. [26] Narrowing the offset (ΔE LE-CT ) between the energy level of the CT state (E CT ) and the lowest excited state (E LE ) may reduce the probability of excitons quenching back to the ground state, which helps in mitigating E loss for a higher V oc . However, the diminished driving force is not in favor of exciton dissociation for a higher J sc , and vice versa. [29] The properties of CT states at the donor-acceptor (D-A) interfaces are supposed to be affected by the morphology Balancing and improving the open-circuit voltage (V oc ) and short-circuit current density (J sc ) synergistically has always been the critical point for organic photovoltaics (OPVs) to achieve high efficiencies. Here, this work adopts a ternary strategy to regulate the trade-off between V oc and J sc by combining the symmetric-asymmetric non-fullerene acceptors that differ at terminals and alkyl side chains to build the ternary OPV (TOPV). It is noticed that the reduced energy disorder and the enhanced luminescence efficiency of TOPV enable a mitigated energy loss and a higher V oc . Meanwhile, the third component, which is distributed at the host donor-acceptor interface, acts as the charge transport channel. The prolonged exciton lifetime, the boosted charge mobility, and the depressed charge recombination promote the TOPV to obtain an improved J sc . Finally, with synergistically improved V oc and J sc , the TOPV delivers an optimal efficiency of 19.26% (certified as 19.12%), representing one of the highest values reported so far.

Conspectus Toward future commercial applications of organic solar cells (OSCs), organic photovoltaic materials that enable high efficiency, excellent stability, and low cost should be developed. Fused-ring electron acceptors (FREAs) have declared that OSCs are capable of showing efficiencies over 19%, whereas stability and cost are not solved yet. As the counterparts of FREAs, non-fused ring electron acceptors (NFREAs) are more flexible in molecular design. They have better stability because of the reduction of intramolecular tension via breaking fused backbone and have more advantages in cost with the reduction of synthetic complexity. However, the challenge for NFREAs is the relatively lower efficiencies (around 15% at current stage), which require better molecular designs for addressing the issues of conformational unicity and effective molecular packing. In this Account, we comprehensively summarize works about NFREAs carried out in our group from three main frameworks, including molecular design and efficiency optimization, material cost, and stability. First, in the part of molecular design and efficiency optimization, the existing rotatable single bond in NFREAs will bring the problem of conformational uncertainty, but it can be solved through proper molecular design, which also regulates the energy levels, light absorption range, and the packing mode of the molecule for obtaining higher performance. Thus, in this part, we discuss the evolution of NFREAs in three aspects, including molecular skeleton optimization, terminal modification, and side chain engineering. Many strategies are used in the design of a molecular skeleton, such as utilizing the quinoid effect, introducing functional groups with the electron push–pulling effect, and using multiple conformational lock. Furthermore, simplifying the skeleton is also the preferred development tendency. As for the terminal, the main modification strategy is adjusting the conjugation length and halogen atoms. What is more, by adjusting the side chain to induce appropriate steric hindrance, we can fix the orientation of molecules, thus regulating molecular packing modes. Second, regarding material cost, we compare the synthesis complexities between state-of-the-art FREAs and NFREAs. Because the synthesis processes of NFREAs reduce the complex cyclization reactions, the synthesis routes are greatly simplified, and the molecule can be obtained through three minimal steps. Third, regarding stability, we analyze the workable strategies used in NFREAs from the views of intrinsic material stability, photostability, and thermal stability. Finally, we conclude the challenges that should be conquered for NFREAs and propose perspectives that could be performed for NFREAs, with the hope of pushing the development of OSCs toward high performance, stability, and low cost.

With the continuous breakthrough of the efficiency of organic photovoltaics (OPVs), their practical applications are on the agenda. However, the thickness tolerance and upscaling in recently reported high‐efficiency devices remains challenging. In this work, the multiphase morphology and desired carrier behaviors are realized by utilizing a quaternary strategy. Notably, the exciton separation, carrier mobility, and carrier lifetime are enhanced significantly, the carrier recombination and the energy loss (Eloss) are reduced, thus beneficial for a higher short‐circuit density (JSC), fill factor (FF), and open‐circuit voltage (VOC) of the quaternary system. Moreover, the intermixing‐phase size is optimized, which is favorable for constructing the thick‐film and large‐area devices. Finally, the device with a 110 nm‐thick active layer shows an outstanding power conversion efficiency (PCE) of 19.32% (certified 19.35%). Furthermore, the large‐area (1.05 and 72.25 cm2) devices with 110 nm thickness present PCEs of 18.25% and 12.20%, and the device with a 305 nm‐thick film (0.0473 cm2) delivers a PCE of 17.55%, which are among the highest values reported. The work demonstrates the potential of the quaternary strategy for large‐area and thick‐film OPVs and promotes the practical application of OPVs in the future.

interface engineering and device architecture design, the power conversion efficiencies (PCEs) of OSCs have been rapidly elevated, with 19.6% for single junction device and 20.2% for tandem device, thus approaching the threshold for potential applications. [4][5][6][7][8][9][10][11][12][13][14] However, rigorous tests of long-term stability for OSCs haven't been well verified, which is another key factor to be considered for competing with other inorganic or perovskite photovoltaic technologies. Nevertheless, to push forward its commercialization, researchers still need to devote efforts to explore strategies that enable improvements in both efficiency and stability for OSCs. [15][16][17][18] In the near-term history of OSCs, ternary blend is one of widely adopted strategies for pursuing higher efficiencies, and blooming everywhere in the state-of-theart OSCs employing Y-series nonfullerene acceptors (NFAs), responsible for the efficiency progress by leaps and bounds. [5,[19][20][21][22][23][24][25][26][27] To explain the efficiency gains, a few working mechanisms have been proposed by researchers, typically like energy/charge transfer, parallel-like, or alloy-like morphology. [28,29] Certainly, in the actual working ternary devices, the introduced third component may stand multiple functions, for which complementary absorption and reduced miscibility of one third component to the host materials allow the co-existing of energy transfer and parallel-like morphology, and cascade energy level alignment and good compatibility of one third component to the host materials enable the co-existing of charge transfer and alloy-like morphology. [30,31] In fact, above situations reflect the dual functions of third component in carrier dynamics management and blend morphology optimization. With device parameters approaching radiative limits, the room of efficiency gains via a ternary blend is limited, especially for OSCs based on Y-series NFAs. This demands the achievement of multiple functions in carrier dynamics and blend morphology for introduced third components in high-performance systems. [32][33][34] Since device stability is also related with carrier dynamics and blend morphology, there may also exist opportunities for ternary blend with multiple functions as the window for improved device stability. [16,17,35,36] Hence, when constructing a successful ternary system, in addition to improved device efficiency via carrier dynamics and blend morphology optimizations, a synergistic improved device stability is also important. Based on above considerations, here Simultaneously achieving improvements in power conversion efficiency (PCE) and stability is the main task of the current development stage of organic solar cells (OSCs). This work reports a symmetry-asymmetry dual-acceptor (SADA) strategy to construct ternary devices, which is found to be feasible for increasing both the PCE and the operational lifetime of OSCs. In this contribution, the symmetric acceptor L8-BO and the asymmetric acceptor BTP-S9 are blended in equ...

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