Y6 Homojunction Organic Solar Cells with Over 5% Power Conversion Efficiency by Controlling the Active Layer Morphology

ABSTRACT Solution‐processable single chromophore homojunction organic solar cells (OSCs) offer a simpler pathway toward device manufacturing and performance reproducibility. However, using a molecule composed of a single chromophore that absorbs light and generates and transports charge efficiently is a challenge. Herein, we report how manipulating the phases in a film can improve the efficiency of homojunction OSCs. Specifically, it is shown that the addition of small amounts of 1,8‐diiodooctane or 1‐chloronaphthalene to a chloroform solution of Y6 can be used to produce a film with different phases. When 1,8‐diiodooctane is used as the additive, the different phases formed provided the energy offset to generate free charge carriers with a maximum internal quantum efficiency of 60%. The optimized Y6 film morphology has electron and hole mobilities of 15.5 ± 1.3 ×10 ⁻⁵ cm ² V ⁻¹ s ⁻¹ and 30.7 ± 3.4 × 10 ⁻⁵ cm ² V ⁻¹ s ⁻¹ , respectively. The best small OSC (0.08 cm ² ) has a power conversion efficiency of 5.4%, with the efficiency of a 1.3 cm ² OSC being a creditable 3.1%. These results show that the latest generation of non‐fullerene acceptors also opens new avenues for the development of simplified large‐scale homojunction OSCs that move beyond the bulk heterojunction approach.