Molecular interaction regulation by adding a third component with high miscibility suppresses the energetic disorder and reduces energy loss for efficient ternary solar cells†

In the advancement of organic solar cells (OSCs), the ternary strategy has emerged as an effective approach for fabricating devices with high photovoltaic performance. In this contribution, we have introduced a novel wide bandgap donor, PBTz-Cl, into the D18:L8-BO binary system to address the excessive aggregation of D18. PBTz-Cl exhibits excellent miscibility with D18 in ternary films due to their similar building blocks. Our findings show that the addition of PBTz-Cl forms a molecular alloy within the amorphous regions of D18. This not only boosts additional exciton generation in D18 through Förster resonance energy transfer, but also suppresses the non-radiative recombination energy loss (ΔE₃) due to the reduced crystallinity difference between D18 and L8-BO by enhancing the crystallinity of L8-BO. The optimized ternary blend film exhibits superior microstructure morphology and enhanced charge dynamics, leading to enhanced photovoltaic performance and remarkable stability. The resulting OSCs show a remarkable increase in performance with a J_SC of 25.30 mA cm⁻², a V_OC of 0.911 V, and an FF of 78.33%. Our study highlights the effectiveness of the strategy, which derives from the synergistic effects of compatible polymer donors to precisely regulate molecular packing and optimize film morphology for improved photovoltaic performance.