Revealing the Molecular Weight Effect on Highly Efficient Polythiophene Solar Cells

Abstract

Polythiophenes (PTs) are promising electron donors inorganic solarcells (OSCs) due to their simple structures and excellent syntheticscalability. Benefiting from the rational molecular design, the powerconversion efficiency (PCE) of PT solar cells has been greatly improved.Herein, five batches of the champion PT (P5TCN-F25) with molecularweights ranging from 30 to 87 kg mol(-1) were prepared,and the effect of the molecular weight on the blend film morphologyand photovoltaic performance of PT solar cells was systematicallyinvestigated. The results showed that the PCEs of the devices improvedfirst and then maintained a high value with the increase of molecularweight, and the highest PCE of 16.7% in binary PT solar cells wasobtained. Further characterizations revealed that the promotion inphotovoltaic performance mainly comes from finer phase separationstructures and more compact molecular packing in the blend film. Thebest device stabilities were also achieved by polymers with high molecularweights. Overall, this study highlights the importance of optimizingthe molecular weight for PTs and offers directions to further improvethe PCE of PT solar cells.