Molecular Ordering Enables High efficiency and Stable All-Polymer Solar Cells Operated in Temperature-Variable Environment

Abstract

All-polymer solar cells (all-PSC) have received vast progress recently. However, the complexity of polymer chain entanglements imposes barrier for improving charge carrier transport and photovoltage gains toward higher photovoltaic performance. Here, we present a study on molecular structure-voltage loss-device stability relationships in all-PSCs based on a group of A-D-A’-D-A type polymer acceptors (PY-IT, PY-DT and PY-FT) in blends with the polymer donor PM6. We show that the conformational rigidify of polymer acceptor plays a decisive role in reducing transport-related energetic disorder (σ) in blends and non-radiative recombination (ΔV_non-rad) for photovoltage loss. Notably, the PM6:PY-DT heterojunction achieves a low σ (0.281 eV), resulting in a low ΔV_non-rad (0.183 V), a high fill factor (78.34), and a PCE of 19.26%. We further show that the reduced energetic and molecular disorder in the all-polymer heterojunction can lead to a phase morphology that is thermally and kinetically more stable under illumination. As a result, ΔV_non-rad growth under light-soaking is suppressed, enabling devices to retain 83% and 91.9% of their initial PCE after 1000 hours of MPP tracking and five thermal cycles (205–353 K), respectively. These findings offer guidance for simultaneously improving efficiency and stability in organic solar cells toward practical applications.