Improving power conversion efficiency (PCE) is important for broadening the applications of organic photovoltaic (OPV) cells. Here, a maximum PCE of 19.0% (certified value of 18.7%) is achieved in single‐junction OPV cells by combining material design with a ternary blending strategy. An active layer comprising a new wide‐bandgap polymer donor named PBQx‐TF and a new low‐bandgap non‐fullerene acceptor (NFA) named eC9‐2Cl is rationally designed. With optimized light utilization, the resulting binary cell exhibits a good PCE of 17.7%. An NFA F‐BTA3 is then added to the active layer as a third component to simultaneously improve the photovoltaic parameters. The improved light unitization, cascaded energy level alignment, and enhanced intermolecular packing result in open‐circuit voltage of 0.879 V, short‐circuit current density of 26.7 mA cm−2, and fill factor of 0.809. This study demonstrates that further improvement of PCEs of high‐performance OPV cells requires fine tuning of the electronic structures and morphologies of the active layers.

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a) E gap was determined from the intersection of the EQE edge and the local EQE maximum; b) V oc was calculated from the measured J-V curves; c) V oc rad was calculated from FTPS and EL measurements; d) EQE EL is the EL quantum efficiency of the fabricated devices; e) Exp. ΔE 3 is calculated with the Equation (ΔE 3 = −kTln(EQE EL )).

OSCs have mainly employed bulk heterojunction (BHJ) structures in the photoactive layers, in which the blend casting (BC) of donor (D) and acceptor (A) materials can form interpenetrating networks with a large D/A interface area for exciton dissociation. However, it is challenging to delicately balance the self-aggregation and miscibility of the two components during the one-step deposition, involving complicated dynamic and kinetic processes. [12] Accordingly, the photovoltaic performances of BC devices depend strongly on the conditions of host solvents, [13] blending ratio of D:A, [14][15][16][17][18] processing additives, [19][20][21][22] and post-treatment. [23] Thus, it is difficult to control the film morphologies, especially the D/A distribution in the vertical direction of BC films, [12] which is closely related to the charge transport and collection.To tailor vertical phase distribution efficiently, the two-step deposition of D and A materials in a sequence, namely, the sequential deposition (SD) method, is considered as an alternative to the BC process. [24][25][26][27][28][29][30][31][32][33] Since the deposition of D and A can be performed independently, the SD OSCs offer unique advantages, including a favored vertical phase distribution and improved film morphology, which provides sufficient D/A interface area, and direct transport pathways for charge carriers. [34][35][36] Obviously, it is beneficial to exciton dissociation and chargeThe variation of the vertical component distribution can significantly influence the photovoltaic performance of organic solar cells (OSCs), mainly due to its impact on exciton dissociation and charge-carrier transport and recombination. Herein, binary devices are fabricated via sequential deposition (SD) of D18 and L8-BO materials in a two-step process. Upon independently regulating the spin-coating speeds of each layer deposition, the optimal SD device shows a record power conversion efficiency (PCE) of 19.05% for binary singlejunction OSCs, much higher than that of the corresponding blend casting (BC) device (18.14%). Impressively, this strategy presents excellent universality in boosting the photovoltaic performance of SD devices, exemplified by several nonfullerene acceptor systems. The mechanism studies reveal that the SD device with preferred vertical components distribution possesses high crystallinity, efficient exciton splitting, low energy loss, and balanced charge transport, resulting in all-around enhancement of photovoltaic performances. This work provides a valuable approach for high-efficiency OSCs, shedding light on understanding the relationship between photovoltaic performance and vertical component distribution.

The ternary strategy, introducing a third component into a binary blend, opens a simple and promising avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The judicious selection of an appropriate third component, without sacrificing the photocurrent and voltage output of the OSC, is of significant importance in ternary devices. Herein, highly efficient OSCs fabricated using a ternary approach are demonstrated, wherein a novel non‐fullerene acceptor L8‐BO‐F is designed and incorporated into the PM6:BTP‐eC9 blend. The three components show complementary absorption spectra and cascade energy alignment. L8‐BO‐F and BTP‐eC9 are found to form a homogeneous mixed phase, which improves the molecular packing of both the donor and acceptor materials, and optimizes the ternary blend morphology. Moreover, the addition of L8‐BO‐F into the binary blend suppresses the non‐radiative recombination, thus leading to a reduced voltage loss. Consequently, concurrent increases in open‐circuit voltage, short‐circuit current, and fill factor are realized, resulting in an unprecedented PCE of 18.66% (certified value of 18.2%), which represents the highest efficiency values reported for both single‐junction and tandem OSCs so far.