16% efficiency all-polymer organic solar cells enabled by a finely tuned morphology via the design of ternary blend

There is an urgent demand for all-polymer organic solar cells (AP-OSCs) to gain higher efficiency. Here, we successfully improve the performance to 16.09% by introducing a small amount of BN-T, a B←N-type polymer acceptor, into the PM6:PY-IT blend. It has been found that BN-T makes the active layer, based on the PM6:PY-IT:BN-T ternary blend, more crystalline but meanwhile slightly reduces the phase separation, leading to enhancement of both exciton harvesting and charge transport. From a thermodynamic viewpoint, BN-T prefers to reside between PM6 and PY-IT, and the fraction of this fine-tunes the morphology. Besides, a significantly reduced nonradiative energy loss occurs in the ternary blend, along with the coexistence of energy and charge transfer between the two acceptors. The progressive performance facilitated by these improved properties demonstrates that AP-OSCs can possibly comparably efficient with those based on small molecule acceptors, further enhancing the competitiveness of this device type. [Display omitted] •16.09% efficiency all-polymer organic solar cell is gained•Ternary blend shows enhanced crystallinity but smaller phase separation length•Large-area devices (0.92 cm2) with 15.45% efficiency are reported All-polymer organic solar cells (AP-OSCs) are the most promising candidate for commercial application compared with other counterparts in view of their flexibility and stability. However, most AP-OSCs’ power conversion efficiencies (PCEs) are significantly lower than those OSCs based on small molecular acceptors (SMAs) (~14% versus ~17%), which has become the biggest problem restricting AP-OSC’s competitiveness. Here, we successfully build a high-performance ternary active layer consisting of the three polymers PM6, PY-IT, and BN-T, affording a PCE of over 16% (16.09%), which is close to state-of-the-art OSCs enabled by SMAs, and the first example of the efficiency of AP-OSCs surpassing 16% as well, a meaningful milestone. We invited our friends in Zhejiang University to reproduce this outstanding result and explore the applicability in large-area fabrication of this ternary design, and the result is exciting that 15.45% PCE was achieved by them for device with active area of 0.92 cm2. Ternary blend PM6:PY-IT:BN-T shows a 16.09% PCE, outperforming its binary counterpart PM6:PY-IT’s 15.11%, together with better operational stability.