composed of both electron donor (D) and acceptor (A), finally, transformed to bulk-heterojunction (BHJ) cells formed between D and A, and BHJ structures were further optimized by introducing additional charge-transporting and/or interfacial layers. [27-29] The objectives of the above modifications in device structure are the same: charges can be generated and extracted more efficiently via appropriate spatial alignment of functional components. Currently, BHJ structure is still the dominant configuration for OPV devices, because it can create sufficient D/A interfaces for charge separation, but exist the risk of obvious charge recombination. [30-36] Since charges are transported and collected in vertical direction within OPV devices, forming a preferred vertical phase distribution to some extent, like donor-enrichment at the anode and acceptor-enrichment at the cathode, is a more ideal morphology to reduce the charge recombination and promote the charge collection efficiencies. [37-39] However, it's a tough task for BHJ structure to form well vertical phase distribution. Especially for non-fullerene acceptor-based OPVs, due to the high similarity in chemical structures between donors and nonfullerene acceptors, it will make thermodynamically D and A mix too well. [40] Therefore, it's a tough challenge for fullerenefree OPVs to realize the desirable vertical phase distribution. To achieve the vertical phase distribution, researchers have developed layer-by-layer (LbL) processing method by sequential depositing D and A layers, so as to form a p-in like morphology. [41-45] There are mainly two ways to construct p-in like morphology: 1) sequentially dissolving and processing D and A components in orthogonal solvents; [46] 2) adopting the blade-coating film-forming technology. [47] Due to the similarity of conjugated backbones and side chains of donors and acceptors, it is challenging to find a pair of orthogonal solvents applicable to various donors and acceptors. However, in most labs, spin-coating is still the most common film processing method, which possesses particular advantages in tuning the BHJ morphology due to the larger shear stress. Thereafter, LbL-type OPVs are less studied and their efficiencies are also largely lagging behind those of BHJ-type counterparts. [48] However, LbL-type OPVs might be more suitable for large-area or roll-to-roll fabrications, because they can offer precise control over the morphology of each layer in mass production. [49-51] Obtaining a finely tuned morphology of the active layer to facilitate both charge generation and charge extraction has long been the goal in the field of organic photovoltaics (OPVs). Here, a solution to resolve the above challenge via synergistically combining the layer-by-layer (LbL) procedure and the ternary strategy is proposed and demonstrated. By adding an asymmetric electron acceptor, BTP-S2, with lower miscibility to the binary donor:acceptor host of PM6:BO-4Cl, vertical phase distribution can be formed with donor-enrichment at the anode and accept...

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Enhancing the luminescence property without sacrificing the charge collection is one key to high-performance organic solar cells (OSCs), while limited by the severe non-radiative charge recombination. Here, we demonstrate efficient OSCs with high luminescence via the design and synthesis of an asymmetric non-fullerene acceptor, BO-5Cl. Blending BO-5Cl with the PM6 donor leads to a record-high electroluminescence external quantum efficiency of 0.1%, which results in a low non-radiative voltage loss of 0.178 eV and a power conversion efficiency (PCE) over 15%. Importantly, incorporating BO-5Cl as the third component into a widely-studied donor:acceptor (D:A) blend, PM6:BO-4Cl, allows device displaying a high certified PCE of 18.2%. Our joint experimental and theoretical studies unveil that more diverse D:A interfacial conformations formed by asymmetric acceptor induce optimized blend interfacial energetics, which contributes to the improved device performance via balancing charge generation and recombination.

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.

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performance, superior flexibility, vivid colors, unique transparency, potential lowcost production with solution processing, etc. [1][2][3][4][5][6][7][8][9] The recent years have witnessed a great leap in device performance and device stability, which are attributed to the delicate molecular structure design, advanced morphology manipulation technology, and device structure evolution. [10][11][12][13][14][15][16][17][18][19] Currently, the best-performed OPVs exhibit a certified efficiency of 19.3% for single junction device and 20.0% for tandem structure, as well as an extrapolated device stability with T 80 over 30 years. [20][21][22] While compared to their inorganic counterparts (e.g., for siliconbased PVs, the efficiency is over 26%), the OPVs are still inferior in efficiency. [23] Therefore, it would be urgent to further improve the device efficiency of OPV, which will require an in-depth understanding on the working principles of OPV, as well as the development of effective strategies to balance the charge generation, transport, and recombination. Among all the strategies, it is generally observed that adding a third component to construct the ternary blend is a very simple but effective method to further boost the device performance of OPVs. [24][25][26][27][28][29][30][31][32] A bunch of benefits have been demonstrated with the multicomponentThe ternary blend is demonstrated as an effective strategy to promote the device performance of organic photovoltaics (OPVs) due to the dilution effect. While the compromise between the charge generation and recombination remains a challenge. Here, a mixed diluent strategy for further improving the device efficiency of OPV is proposed. Specifically, the high-performance OPV system with a polymer donor, i.e., PM6, and a nonfullerene acceptor (NFA), i.e., BTP-eC9, is diluted by the mixed diluents, which involve a high bandgap NFA of BTP-S17 and a low bandgap NFA of BTP-S16 (similar with that of the BTP-eC9). The BTP-S17 of better miscibility with BTP-eC9 can dramatically enhance the open-circuit voltage (V OC ), while the BTP-S16 maximizes the charge generation or the short-circuit current density (J SC ). The interplay of BTP-17 and BTP-S16 enables better compromise between charge generation and recombination, thus leading to a high device performance of 19.76% (certified 19.41%), which is the best among single-junction OPVs. Further analysis on carrier dynamics validates the efficacy of mixed diluents for balancing charge generation and recombination, which can be further attributed to the more diverse energetic landscapes and improved morphology. Therefore, this work provides an effective strategy for highperformance OPV for further commercialization.

facades, roofs, etc. [1-4] Criteria to evaluate the performance of (semi-)transparent photovoltaic (ST-PV) include power conversion efficiency (PCE), averaged photopic transmittance (APT), and color rendering index (CRI), which indicates how good the original color is retained. [5] Since the light-absorbing and transmittance seem a paradox for PV devices, the light utilization efficiency (LUE), a product of PCE and APT (LUE = PCE × APT), is proposed to judge the performance of ST-PV. [4,5] Considering that the solar energy comprises photons of different energies or wavelengths (including both the visible and invisible photons), an ideal ST-PV device should make full use of the invisible photons to achieve high PCE, while allowing most of the visible photons to penetrate through for sake of high APT and CRI. [6-8] Thereafter, photovoltaic devices with good absorbing selectivity, that is, the ability to selectively absorb the near-infrared (NIR) photons and transmit the visible ones, are highly favored for high-performance ST-PV. Theoretically, the maximum LUE of single-junction ST-PV can reach over 20% with absolute selective absorbing property (Figure 1a). [9] While, the practical record LUE can only reach 5.7%, even with the tandem structure. [10] The huge gap can be attributed to the poor absorbing selectivity of ST-PV. [11-13] Particularly, energy band principle excludes most of the high-efficiency photovoltaic materials for ST-PV application. For example, although the inorganic photovoltaic materials, such as silicon, CIGS, CdTe, GaAs, etc, exhibit excellent performance approaching the S-Q limit and NIR absorbing properties, the energy band principle determines their strong absorption in the visible region (≈0% APT) and thus poor selective absorption. [14-16] As a result, these materials are seldom considered for ST-PV application. Fortunately, the semi-transparent organic photovoltaic (ST-OPV) device seems one exception to break the curse of energy band principle to fulfill good selective absorption. The organic semiconductors typically exhibit vibronic lightabsorbing features, which show peaks and valleys in different absorbing regions. Moreover, their absorption profiles can be easily tailored via modifying the molecular structures, rendering more space to realize good absorption selectivity. [17-20] Indeed, tremendous efforts have been devoted to explore high-performance ST-OPV. Particularly, developing the high-performance low band Semi-transparent organic photovoltaics (ST-OPVs) are promising solar windows for building integration. Improving the light-absorbing selectivity, that is, transmitting the visible photons while absorbing the invisible ones, is a key step toward high-performance ST-OPV. To achieve this goal, the optical properties of the active layer, transparent electrode, and capping layer are comprehensively tailored, and a highly efficient ST-OPV with good absorbing selectivity is demonstrated. First, a numerical method is established to quantify the absorbing selectivity of materials and d...

The absorption of nonfullerene acceptors (NFAs) at near-infrared (NIR) regions is crucial for obtaining high current densities in organic solar cells (OSCs). Herein, two narrow-band gap NFAs with unfused backbones possessing broad (600–900 nm) and strong absorption are developed by the conjugation of a benzothiadiazole core to halogenated end groups through a cyclopentadithiophene bridge. Compared with the fluorinated counterpart BCDT-4F, the chlorinated NFA BCDT-4Cl shows stronger J-aggregation and closer molecular packing, leading to an optimized blend morphology when paired with the polymer donor, PBDB-T. Thus, an obvious improvement in external quantum efficiency response was obtained for BCDT-4Cl-based OSCs, presenting a higher efficiency of 12.10% than those (9.65%) based on BCDT-4F. This work provides a design strategy for NIR acceptors in the combination of electron-deficient core and halogenated terminal in unfused backbones, which results in not only fine-tuning the optoelectronic properties but also simplifying the synthetic complexities of molecules.