The isomerization effect of a benzothiophene-substituted benzodithiophene-based donor polymer on the blend morphology and photovoltaic performance of all-polymer solar cells

All-polymer solar cells (all-PSCs) show great promise for use as portable and wearable electronic power sources. It is well recognized that a gradient distribution of the two components of the active layer of all-PSCs is preferred to facilitate charge transport and suppress non-radiative recombination loss. Herein, two polymers of PBS-DIT and PTPH-DIT were designed and synthesized by changing the linking mode of a benzothiophene side chain located on a benzodithiophene (BDT) skeleton, and the influences of isomerization on the blend morphology and device performance were investigated. PBS-DIT with the BDT moiety linked to the benzene ring of benzothiophene exhibited stronger solution aggregation, better tolerance to heat processing, and finer compatibility with the acceptor of N2200. Besides, PBS-DIT induced its desirable vertical phase distribution while PTPHT-DIT was uniformly distributed over the vertical direction. Benefiting from more efficient charge transfer, higher and balanced charge transport, and less recombination loss, the all-PSCs with PBS-DIT afforded a PCE of 7.76% which is much higher than 5.31% for the blend of PTPH-DIT:N2200. The results indicate that the building block of BDT linked to the benzene ring of the benzothiophene substituent is more promising than its counterpart of BDT linked to the thiophene ring of the benzothiophene substituent. Furthermore, isomerization can be a simple yet effective method to modulate the intermolecular miscibility and vertical phase distribution. Two polymers of PBS-DIT and PTPH-DIT were designed and synthesized, and the influence of isomerization on the blend morphology and device performance was investigated.