Morphology Control of D-A-D and D-A-A Type Donor Polymers via Thiophene-π-Siloxane Spacer Engineering to Produce Scalable High-Performance Organic Photovoltaics

One of the major challenges for the commercial application of high performance organic solar cells (OSCs) is scaling them from small-area devices to large-area submodules (LA-SMs). Here, we report the design and synthesis of two new π-conjugated spacer-functionalized donor polymers (SF-DPs), D-A-D-π-siloxane (SCl-SiO) and D-A-alkyl-A (SCl-6C), which incorporate thiophene-π-siloxane and hexyl alkyl spacer units into a benzodithiophene (BDT) and benzodithiophenedione (BDD) backbone. A promising technique for enhancing the charge transport, morphology, and stability of OSC devices is the use of spacers, which are designed polymer donors with specific side-chain functionalities. By applying this strategy to LA-SMs (55 cm²) processed via non-halogenated solvent (o-xylene) and bar coating, a record PCE of about 15.5% was attained with remarkable operational stability (> 88%) of original PCE during prolonged light soaking and environmental stress tests. Additionally, small-area devices exhibited outstanding power conversion efficiencies (PCEs) exceeding 18% (PM6: SCl-SiO (HMw): Y6-BO) with reduced bimolecular recombination, enhanced charge mobilities, and well defined nanostructures confirmed by AFM, TEM, and GIWAX analyzes. These results indicate that side chain engineering with thiophene-π siloxane and hexyl alkyl incorporated spacer units, in conjunction with controlled molecular weight, provides a scalable pathway toward production of stable and highly efficient OSC modules. (Figure presented.).