Halogen-Engineered Thiophene Additives Enable High-Performance Layer-by-Layer Organic Solar Cells With 20.12% Efficiency

Abstract

Organic solar cells (OSCs) have emerged as promising candidates for next-generation photovoltaics, yet traditional bulk heterojunction (BHJ) devices face inherent limitations in morphology control and phase separation. Layer-by-layer (LbL) processing with a p–i–n configuration offers an innovative solution by enabling precise control over donor–acceptor distribution and interfacial characteristics. Here, we systematically investigate nine halogen-functionalized additives across three categories—methyl halides, thiophene halides, and benzene halides—for optimizing LbL device performance. These additives, distinguished by their diverse thermal properties and solid–liquid transformation capabilities below 100°C, are functionalized as both nucleation centers and morphology-modulating plasticizers during thermal treatment. Among them, 2-bromo-5-iodothiophene (BIT) demonstrates superior performance through synergistic effects of its bromine–iodine combination and thiophene core in mediating donor–acceptor interactions. LbL devices processed with BIT achieve exceptional metrics in the PM6/L8-BO system, including a open-circuit voltage of 0.916 V, a short-circuit current density of 27.12 mA cm⁻², and an fill factor of 80.97%, resulting in an impressive power conversion efficiency of 20.12%. This study establishes a molecular design strategy for halogen-functionalized additives that simultaneously optimizes both donor and acceptor layers while maintaining processing simplicity for potential industrial applications.

Keywords

halogen engineering / LbL processing / morphology optimization / organic solar cells / volatile additives

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