Intramolecular Lock Conjugated Polymer Electrolytes as the Cathode Interfacial Layer for Nonfullerene Organic Solar Cells

D–A polymers exhibit excellent intramolecular charge transfer (ICT) properties due to the differences in energy levels. However, bulky dihedral angles between D and A units with conjugated structures have a negative impact on the process of ICT, which inhibits efficient electron transport between adjacent conjugated units. To solve this problem, the noncovalent conformational locks were constructed by the introduction of π-bridges. Intriguingly, thiophene π-bridges containing sulfur elements can form S─H noncovalent conformational locks, which not only extend the conjugated structure to overcome the steric hindrance but also enhance the efficiency of charge transport. Therefore, PFPy-TT and PFPy-TTBT with conformational locks exhibited superior short-circuit density (JSC) compared to PFPy-BT without conformational locks. Meanwhile, PFPy-TTBT with a benzothiazole moiety exhibits stronger ICT properties and better electron extraction efficiency compared to PFPy-TT without a D–A structure. The enhanced ICT properties enable PFPy-TTBT to have better intramolecular and intermolecular electron transport performance, realizing a power conversion efficiency (PCE) of 16.15%. By constructing noncovalent conformational locks using π-bridges in cathode interfacial layers (CILs), the problem of inferior coplanarity is resolved, and favorable molecular alignment is promoted, while also demonstrating exceptional storage, light, heat, and air stability. A device with PFPy-TTBT maintains over 80% of its initial PCE value when stored in nitrogen condition for 120 h. These advances hold promise for improving charge transfer and film quality in organic solar cells.