Engineering photoactive layer towards high-performance organic solar cells

Abstract

Engineering photoactive layers of organic solar cells (OSCs) by introducing an additive or guest component has been the most widely used method to enhance the performance of OSCs. However, with the evolution of organic light-absorbing materials, traditional additive strategies or guest materials cannot realize the maximum potential of state-of-­the-art OSCs with non-fullerene acceptors (NFAs). Therefore, this thesis proposes three strategies to engineer photoactive layers toward high-performance OSCs. The first work demonstrates a simple and versatile solid additive, 1,4-diiodobenzene (DIB). Due to the formation of a eutectic phase between the additive and the NFA, a desired microstructure with tighter molecular stacking and more ordered molecular arrangement is achieved. As a result, DIB-treated OSCs display significantly enhanced performance with excellent device stability. Additional advantages of the DIB treatment include toleration of a wide additive concentration range, and versatility in both polymer and small molecule OSCs. The results highlight the importance of additive engineering in high-performance OSCs and demonstrate the significance of supramolecular interactions. The second work aims to achieve highly efficient OSCs with suppressed non-radiative recombination loss suppression. In this work, we developed a non-monotonic intermediate state manipulation strategy for state-of-the-art OSCs by employing 1,3,5-trichlorobenzene (TCB) as a crystallization regulator, which optimizes the film crystallization process, manipulates the self-organization of bulk-heterojunction in a non-monotonic manner, i.e., first enhancing and then relaxing the molecular aggregation. As a result, the excessive aggregation of non-fullerene acceptors is avoided, and we have achieved efficient organic solar cells with reduced non-radiative recombination loss. In the PM6:BTP-eC9 OSC, our strategy successfully offers a record binary organic solar cell efficiency of 19.31% (18.93% certified) with very low non-radiative recombination loss of 0.190 eV. And lower non-radiative recombination loss of 0.168 eV is further achieved in the PM1:BTP-eC9 OSC (19.10% efficiency), giving great promise to future OOSC research. The third work is a successful attempt to design and synthesize a NFA guest component for high-performance OSCs. Herein, guided by theoretical calculation, we present a rationally designed NFA, o-BTP-eC9, with much lower synthetic complexity and distinct photoelectric properties than the benchmark BTP-eC9. Moreover, the new NFA o-BTP-eC9 has excellent miscibility, crystallinity, and energy level compatibility with BTP-eC9, which enables a PCE of 19.9% (19.5% certified) in PM6:BTP-C9:o-BTP-eC9 based ternary system with enhanced stability. Our strategies enabled emerging NFA OSCs to achieve continuous performance breakthroughs. Moreover, we deeply investigated the working mechanisms behind the high performance and proposed non-monotonic intermediate state transition induced by additive for the first time. We hope these works can provide insightful guidance for OSC research and inspire more meaningful explorations in this field.