High Miscibility‐Induced Reduction of Trap Density in All‐Polymer Solar Cells Using Hybrid Cyclohexyl‐Hexyl Side Chains

Reducing the trap density within organic solar cells is of vital importance to realize high power conversion efficiency (PCE); however, research focusing on this aspect is limited in all‐polymer solar cells (All‐PSCs). In this work, it is found that the trap density can be dramatically reduced by simultaneously obtaining high miscibility of donor and acceptor and ordered packing in blend films through substituting ethylhexyl with hybrid cyclohexyl‐hexyl side chains in the design of the polymer donor. D18‐ChCl with hybrid cyclohexyl‐hexyl chains has a slightly lower aggregation behavior relative to the D18‐Cl counterpart, but reveals synchronously higher miscibility and crystallinity in a blend with the acceptor PYF‐T‐o. Such a morphology evolution positively affects the electronic properties of the device—prolongs the carrier lifetime, facilitates exciton dissociation, and lowers the energy disorder. As a result, the All‐PSC devices based on D18‐ChCl exhibited a remarkable PCE of 17.1%, with a low trap density of 2.65 × 1015 cm−3, a low energy disorder of 47 meV as well as outstanding stability and mechanical durability. This result demonstrates that hybrid cyclohexyl‐hexyl alkyl engineering delicately improves miscibility, drives low trap density, and refines device performance, which brings vibrancy to the All‐PSC research field. As an analog of D18‐Cl, the new polymer donor D18‐ChCl is designed by substituting the 2‐ethylhexyl side chains with cyclohexyl‐hexyl chain. Using PYF‐T‐o as the acceptor, the D18‐ChCl blend realizes an interpenetrating network constituting of smaller phase separation, and higher miscibility and crystallinity. Such a morphology evolution reduces energy disorder and trap density, which ultimately boosts the power conversion efficiency from 12.3% to 17.1%.