Vacuum-assisted vertical component distribution in pseudo-bulk heterojunctions: a pathway to high-performance and stable organic solar cells

Precise control over the vertical component distribution and molecular packing within the photoactive layer is paramount for achieving high-performance organic solar cells (OSCs). However, optimizing these parameters in sequentially deposited pseudo-bulk heterojunction (p-BHJ) architecture remains challenging, often limited by inefficient self-assembly of organic semiconductors. In this work, a post-treatment combining vacuum and thermal annealing (VTA) is adopted. A range of morphological measurements demonstrate that compared with the traditional thermal annealing (TA) treatment, VTA can accelerate solvent evaporation, promoting the crystallization of acceptor at the top surface and inhibiting excessive intermixing between donor and acceptor, and therefore leads to a more stratified p-i-n configuration with interpenetrated donor-acceptor networks. This morphology modulation enhances carrier mobility and suppresses charge recombination, culminating in a champion power conversion efficiency (PCE) of 20.5% for binary OSCs. Furthermore, due to the enhanced crystallinity and more compact molecular packing, the optimized film also exhibits exceptional photo and morphological stability, achieving a <i>T</i> ₈₀ of over 3900 hours in a conventional ITO/PEDOT:PSS/PM6/L8-BO/PDINN/Ag structure, and 54 000 h in an interfacial-stable ITO/MoO₃/PM6/L8-BO/C₆₀/BCP/Ag structure, under the continuous one-sun illumination with a criterion of ISOS-L-1.