as PM6 [13,14] and PBDB-T [15] with narrow bandgap nonfullerene acceptors (A), for example, IT-4F, [14] and Y6 [8] has remained as a wise strategy to absorb solar irradiation in the range of 500-900 nm or even up to a broader absorption region. However, solar irradiation in the spectrum range of 300-500 nm remains unabsorbed. The construction of ternary device by introducing a third component into the photoactive layer has been proven to overcome this issue effectively, where full utilization of solar irradiation in the entire solar spectrum can be realized without complicating the traditional fabrication processes. [16][17][18][19][20][21][22][23] Fullerene derivatives like phenyl-C71-butyric-acid-methyl ester (PC 71 BM) with the main absorption in the range of 300-500 nm have been commonly used as a third component to strengthen the light-harvesting capability of active layers, thus providing a potential route to enhance the short-circuit current density (J sc ) and PCE. [24] Some recent theoretical models and mechanisms have been proposed to provide guide and reference for future development of ternary devices. [25][26][27] Among them, three models which include charge transfer model, [17] energy transfer model, [28] and parallel-like or alloy-like model [16,29] have been widely accepted. In the charge transfer model, the third component in the active layer participates in the process of exciton dissociation and charge carrier generation in the donor/ acceptor interface. [22,30] A cascaded energy level distribution is the requirement for such mechanisms to take place. [31] In contrast, in the energy transfer model, the third component serves as an "energy donor" which absorbs additional solar energy and delivers it to donor or acceptor by Förster or Dexter energy transfer. [32] Ternary devices based on charge transfer or energy transfer mechanisms improve J sc by utilizing additional solar energy. [33,34] Ternary devices based on charge transfer mechanism will affect the open-circuit voltage (V oc ) while the devices based on energy transfer mechanism can hardly impact the V oc due to their roles in charge transfer and dissociation. [35] The third one is the parallel-like or alloy-like model, of which the mechanism does not require any certain energy levels.In parallel-like model, the third component serves as a donor (or acceptor) and work independently with another donor (or acceptor). [36] The ternary device can be viewed as two subcells that are mixed together. For the alloy-like model, the third component is finely mixed with one of the host components to form a two-phase morphology. In this process, dual donors Ternary heterojunction strategies appear to be an efficient approach to improve the efficiency of organic solar cells (OSCs) through harvesting more sunlight. Ternary OSCs are fabricated by employing wide bandgap polymer donor (PM6), narrow bandgap nonfullerene acceptor (Y6), and PC 71 BM as the third component to tune the light absorption and morphologies of the blend films. A record power conver...

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Herein, a simple “Same-A-Strategy” (SAS), constructing p-type and n-type photovoltaic materials with the same electron-accepting (A) unit of benzotriazole, is adopted to initially control the energy offsets. Then, chlorine atoms are introduced into the conjugated side chain of the benzo­[1,2-b:4,5-b′]­dithiophene (BDT) donor unit of the p-type polymer to fine-tune the optoelectronic properties. The chlorinated polymer J52-Cl, blended with a non-fullerene small molecule acceptor BTA3, yields the very small energy offsets (ΔE HOMO = 0.10 eV, ΔE LUMO = 0.28 eV) and the decreased nonradiative recombination loss of 0.24 eV. Benefiting from the strong molecular aggregation, ordered molecular orientation, and fine film morphology, J52-Cl:BTA3 device delivers balanced carriers mobilities and also suppressed charge recombination losses. Consequently, the obtained device yields a very high open-circuit voltage (V OC) of 1.24 V, a short-circuit current (J SC) of 13.16 mA cm–2, and a fill factor of 66.62%, giving rise to a promising power conversion efficiency (PCE) of 10.5%, which is a large breakthrough for organic solar cells with high V OC beyond 1.20 V. Our results provide a rare opportunity to break through the limitation of the problematic trade-off between energy loss and PCE and show a great potential for the application in tandem solar cells.