PM6/L8-BO Thin Films through Layer-by-Layer Engineering: Formation Mechanism, Energetic Disorder, and Carrier Mobility

Abstract

Layer-by-layer (LBL) process has emerged as a promising method in the advancement of organic photovoltaics, emphasizing scalability and reproducibility. More importantly, it provides enhanced morphological control for boosting carrier mobility (μ) and power conversion efficiency. By employing a multiscale approach that combined first-principles calculations, molecular dynamics simulations, and kinetic Monte Carlo methods, the relationship between LBL morphology engineering and carrier mobility in donor/acceptor (PM6/L8-BO) thin films is elucidated. During solvent evaporation, the order of solid-phase formation in LBL films was top surface, bottom region, and then the middle region. The early solid precipitation from precursor solutions was acceptor, resulting in a well-ordered molecular arrangement and reducing energy disorder of acceptor LUMO levels. Furthermore, the difference in energy disorders between the A/D blend region and the pure A or D domains enabled LBL morphology engineering to balance electron and hole mobilities, thereby mitigating charge accumulation and recombination. LBL-manufactured films presented higher carrier mobility ({\mu }_{\text{e}}^{\text{LBL}}={\mu }_{\text{h}}^{\text{LBL}}=1.9\times {10}^{-3} cm² V⁻¹ s⁻¹) compared to bulk heterojunction (BHJ) films ({\mu }_{\text{e}}^{\text{BHJ}}>{\mu }_{\text{h}}^{\text{BHJ}}=0.1\times {10}^{-3} cm²·V⁻¹ s⁻¹). These mechanisms provided insights into strategies for enhancing charge extraction of photo-generated charge carriers through LBL engineering, driving the development of efficient organic photovoltaic materials.

Keywords

PM6/L8-BO organic solar cells / carrier mobility / layer-by-layer / energy disorder

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