Polymer Donors with Temperature-Insensitive, Strong Aggregation Properties Enabling Additive-Free, Processing Temperature-Tolerant High-Performance All-Polymer Solar Cells

In this work, the impact of temperature-dependent aggregation behaviors in benzodithiophene (BDT)-based polymer donors (PDs) on the electrical, morphological, and photovoltaic performances of all-polymer solar cells (all-PSCs) is investigated. Two PDs, PBDB-T and PBDB-Bz, with thienyl or benzothienyl side chains and identical backbones are prepared. In contrast to PBDB-T, PBDB-Bz with bulkier side chains exhibits strong aggregation behavior in solution independent of temperatures between 20 and 100 °C. Notably, PBDB-Bz-based all-PSCs show a power conversion efficiency (PCE) of over 9% without any solvent additives (SAs) or thermal annealing (TA), whereas these treatments are inevitable in optimizing the PCE of PBDB-T-based all-PSCs. Furthermore, high PCEs for the PBDB-Bz-based devices are maintained, irrespective of their processing temperature (Tproc). However, the PCEs of PBDB-T-based devices are strongly dependent on their SA, TA, and Tproc conditions. This phenomenon is due to the robust nature of the domain crystallinity and blend morphology of PBDB-Bz blends at different Tprocs, resulting in Tproc-tolerant charge mobilities and PCE values. Thus, the development of PDs with temperature-insensitive, strong aggregation behavior is crucial in producing reproducible, Tproc-tolerant, and additive-free high-performance all-PSC devices.