Donor-Acceptor Alternating Copolymer Compatibilizers for Thermally Stable, Mechanically Robust, and High-Performance Organic Solar Cells

Small-molecule acceptor (SMA)-based organic solar cells (OSCs) have achieved high power conversion efficiencies (PCEs), while their long-term stabilities remain to be improved to meet the requirements for real applications. Herein, we demonstrate the use of donor-acceptor alternating copolymer-type compatibilizers (DACCs) in high-performance SMA-based OSCs, enhancing their PCE, thermal stability, and mechanical robustness simultaneously. Detailed experimental and computational studies reveal that the addition of DACCs to polymer donor (P_D)-SMA blends effectively reduces P_D-SMA interfacial tensions and stabilizes the interfaces, preventing the coalescence of the phase-separated domains. As a result, desired morphologies with exceptional thermal stability and mechanical robustness are obtained for the P_D-SMA blends. The addition of 20 wt % DACCs affords OSCs with a PCE of 17.1% and a cohesive fracture energy (G_c) of 0.89 J m^-2, higher than those (PCE = 13.6% and G_c = 0.35 J m^-2) for the control OSCs without DACCs. Moreover, at an elevated temperature of 120 °C, the OSCs with 20 wt % DACC exhibit excellent morphological stability, retaining over 95% of the initial PCE after 300 h. In contrast, the control OSCs without the DACC rapidly degraded to below 60% of the initial PCE after 144 h.

High-Molecular-Weight Electroactive Polymer Additives for Simultaneous Enhancement of Photovoltaic Efficiency and Mechanical Robustness in High-Performance Polymer Solar Cells

The development of small-molecule acceptors (SMAs) has significantly enhanced the power conversion efficiency (PCE) of polymer solar cells (PSCs); however, the inferior mechanical properties of SMA-based PSCs often limit their long-term stability and application in wearable power generators. Herein, we demonstrate a simple and effective strategy for enhancing the mechanical robustness and PCE of PSCs by incorporating a high-molecular-weight (MW) polymer acceptor (P _A, P(NDI2OD-T2)). The addition of 10-20 wt % P _A leads to a more than 4-fold increase in the mechanical ductility of the SMA-based PSCs in terms of the crack onset strain (COS). At the same time, the incorporation of P _A into the active layer improves the charge transport and recombination properties, increasing the PCE of the PSC from 14.6 to 15.4%. The added P _As act as tie molecules, providing mechanical and electrical bridges between adjacent domains of SMAs. Thus, for the first time, we produce highly efficient and mechanically robust PSCs with a 15% PCE and 10% COS at the same time, thereby demonstrating their great potential as stretchable or wearable power generators. To understand the origin of the dual enhancements realized by P _A, we investigate the influence of the P _A content on electrical, structural, and morphological properties of the PSCs.